Resmed Co-Trimoxazole Oral Susp

Indications

• Bacterial infections
• Urinary tract infections
• Respiratory tract infections
• Prophylaxis of recurrent urinary tract infections

Dosage

Children: For children aged 6 weeks to 5 months: 4 mg/kg twice daily (max. 200 mg). For children 6 months to 5 years: 4 mg/kg twice daily (max. 200 mg). For children 6–11 years: 4 mg/kg twice daily (max. 200 mg). For children

Adults: 200 mg twice daily.

Mechanism of action

Trimethoprim is a reversible inhibitor of dihydrofolate reductase, an enzyme that catalyzes the formation of tetrahydrofolic acid from dihydrofolic acid. By inhibiting this enzyme, trimethoprim disrupts the biosynthesis of nucleic acids and proteins in bacteria, leading to their growth inhibition. The drug has a significantly higher affinity for bacterial dihydrofolate reductase compared to the mammalian enzyme, ensuring selective antibacterial activity.

Pharmacodynamics

Trimethoprim exerts its antimicrobial effects by disrupting bacterial nucleic acid synthesis. It is effective against various gram-negative bacteria and some coagulase-negative Staphylococcus species. Resistance can develop through mechanisms such as alterations to the bacterial cell wall or overproduction of the target enzyme. Monitoring for potential blood disorders is important during therapy, as rare adverse effects can occur.

Pharmacokinetics

Trimethoprim is well absorbed from the gastrointestinal tract and reaches peak plasma concentrations within 1-4 hours post-administration. It has a volume of distribution that suggests extensive tissue penetration, including into the lungs and kidneys, and is primarily excreted unchanged in the urine. The elimination half-life is approximately 8-10 hours, and dosing adjustments may be necessary in cases of renal impairment.

Contra-indications

• Severe renal impairment
• Known hypersensitivity to trimethoprim or any component of the formulation

Adverse effects

• Diarrhoea
• Nausea
• Headache
• Dizziness
• Fatigue
• Skin reactions
• Vomiting
• Anxiety
• Agranulocytosis
• Eosinophilia
• Photosensitivity reactions
• Thrombocytopenia
• Leukopenia
• Pseudomembranous colitis

Interactions

• Increases exposure to pramipexole
• Increases exposure to treprostinil
• Increases exposure to dopaminergic receptor agonists
• Increases concentration of antiepileptics
• Increases concentration of fosphenytoin
• Increases concentration of phenytoin
• Increases risk of haematological toxicity with azathioprine in renal transplant patients
• Increases concentration of digoxin
• Increases exposure to repaglinide

Precautions

• Caution in patients with renal impairment
• Caution in elderly patients (75 years and over)
• Monitor for signs of blood disorders such as sore throat, fever, and pallor
• Consider local antimicrobial susceptibility patterns before use

Pregnancy

Manufacturer advises avoidance due to potential fetal developmental toxicity observed in animal studies.

Breast-feeding

Manufacturer advises avoidance as trimethoprim is present in milk in animal studies.

Storage

Store in a cool, dry place, away from direct sunlight. Keep out of reach of children.

Formulations

• Tablets
• Oral suspension
• Injection solution

Indications

• Food preservative
• Treatment of urea cycle disorders
• Metabolic disorders involving benzoyl-CoA

Dosage

Children: Refer to the BNF for Children for specific dosing guidelines based on condition.

Adults: Refer to the BNF for specific dosing guidelines based on condition.

Mechanism of action

Benzoate acts mainly by inhibiting the growth of bacteria and fungi through its ability to lower the pH, creating an environment that is less favorable for microbial growth. It is also involved in metabolic pathways where it helps in the conjugation of toxic substances, facilitating their excretion from the body.

Pharmacodynamics

Benzoate is known for its antimicrobial properties, which are particularly effective against a wide range of fungi and bacteria. Its efficacy as a preservative is due to its ability to penetrate microbial cell membranes and disrupt their metabolic processes. Additionally, it has been observed to modulate various metabolic pathways, particularly those associated with aromatic compound degradation.

Pharmacokinetics

After ingestion, benzoate is rapidly absorbed in the gastrointestinal tract. It is metabolized primarily in the liver, where it undergoes conjugation with glycine to form hippurate, which is then excreted in the urine. The half-life of benzoate varies depending on individual metabolic rates but is generally short due to its efficient conversion and excretion.

Pregnancy

There is limited data on the use of benzoate in pregnancy. Consultation with healthcare professionals is advised before use.

Breast-feeding

Limited data is available on the excretion of benzoate in breast milk. Caution is recommended when administering to nursing mothers.

Storage

Store in a cool, dry place away from direct sunlight. Keep out of reach of children.

Indications

• Dry eye syndrome
• Ocular lubrication
• Thickening agent in pharmaceutical formulations
• Food industry as a stabilizer and emulsifier

Dosage

Children: For paediatric use, refer to specific product guidelines and consult a healthcare professional for appropriate advice.

Adults: For dry eye treatment, apply as needed, typically 1 drop in each affected eye. Refer to specific product guidelines for exact formulation and frequency.

Mechanism of action

Carboxymethylcellulose works by forming a gel-like structure when it interacts with water, which helps retain moisture and provide lubrication. In ophthalmic applications, it acts as a protective agent for the ocular surface, reducing friction and providing comfort to patients with dry eye conditions.

Pharmacodynamics

The pharmacodynamic properties of carboxymethylcellulose are primarily related to its ability to increase viscosity and improve the stability of formulations. It does not undergo significant systemic absorption and exerts its effects locally, particularly in the gastrointestinal tract and on the ocular surface as a lubricant.

Pharmacokinetics

Carboxymethylcellulose is not absorbed significantly through the gastrointestinal tract when ingested, and its systemic bioavailability is negligible. When used in ophthalmic formulations, it acts locally on the eye without significant systemic effects. The elimination pathway is primarily through natural degradation and excretion of unabsorbed material.

Adverse effects

• Allergic reactions
• Skin irritation
• Gastrointestinal discomfort

Precautions

• Use with caution in patients with known hypersensitivity to cellulose derivatives
• Monitor for allergic reactions

Pregnancy

Carboxymethylcellulose is generally considered safe during pregnancy as it is not absorbed systemically.

Breast-feeding

Carboxymethylcellulose is considered safe during breastfeeding as it is not absorbed systemically.

Storage

Store in a cool, dry place away from direct sunlight.

Formulations

• Eye drops
• Oral suspensions
• Topical gels

Indications

• Hypovolemic shock
• Severe burns
• Postoperative fluid replacement
• Sepsis
• Trauma management

Dosage

Children: Refer to established guidelines for specific dosing, as it varies based on the type of colloidal solution used and the clinical condition being treated.

Adults: Refer to established guidelines for specific dosing, as it varies based on the type of colloidal solution used and the clinical condition being treated.

Mechanism of action

Colloidal solutions work by maintaining oncotic pressure in the blood, thus helping to retain fluid within the vascular system. This is primarily due to the large molecular weight of the colloidal particles, which cannot easily pass through capillary walls. The presence of colloids in the blood helps to draw water into the circulation, increasing blood volume and improving tissue perfusion.

Pharmacodynamics

The pharmacodynamics of colloidal solutions are centered on their ability to exert osmotic pressure, which helps maintain blood volume and pressure. This effect is particularly important in conditions such as hypovolemia and shock, where fluid replacement is necessary to restore hemodynamic stability. The efficacy of colloidal solutions can vary depending on the type of colloid used, as well as the underlying clinical condition being treated.

Pharmacokinetics

Colloidal solutions are typically administered intravenously and their pharmacokinetics can vary based on the specific formulation. Generally, colloids are distributed throughout the vascular compartment and have a longer duration of action compared to crystalloids, as they remain in circulation longer. The elimination of colloids is primarily through the reticuloendothelial system, where they are metabolized or eliminated by the liver and spleen. Factors such as particle size and composition can influence their distribution and clearance.

Adverse effects

• Allergic reactions
• Injection site reactions
• Nausea
• Vomiting
• Headache
• Fever

Precautions

• Use with caution in patients with known allergies to any component of the formulation
• Monitor for signs of hypersensitivity during administration
• Consider volume overload in patients with cardiac or renal impairment

Pregnancy

The safety of colloidal solutions during pregnancy has not been established. Use only if the potential benefit justifies the potential risk to the fetus.

Breast-feeding

It is not known whether colloidal solutions are excreted in human milk. Caution should be exercised when administering to breastfeeding mothers.

Storage

Store at room temperature, protect from light, and do not freeze. Keep out of reach of children.

Formulations

• Colloidal silver
• Colloidal gold
• Colloidal iron
• Other metal colloids

Indications

• Monitoring respiratory function
• Assessment of metabolic status
• Management of respiratory acidosis
• Management of respiratory alkalosis

Dosage

Children: Dosing for interventions related to carbon dioxide levels in pediatric patients should be guided by clinical protocols and the BNF for Children.

Adults: Dosing for interventions related to carbon dioxide levels is typically based on clinical assessment and individual patient needs. Refer to clinical guidelines for specific scenarios.

Mechanism of action

Carbon dioxide acts primarily as a signaling molecule in the body, influencing respiratory drive and blood pH. It is produced during cellular respiration and is a critical component of the bicarbonate buffering system, which helps maintain acid-base homeostasis. Elevated levels of CO2 in the blood stimulate ventilation in the lungs, increasing the rate of gas exchange and facilitating the removal of excess CO2.

Pharmacodynamics

The pharmacodynamic effects of dioxides, particularly carbon dioxide, are closely related to its concentration in the blood. As CO2 levels increase, it leads to respiratory acidosis, which can stimulate the respiratory centers in the brain to increase ventilation. Conversely, low levels of CO2 can cause respiratory alkalosis, potentially leading to decreased respiratory drive. CO2 also plays a role in vasodilation and can affect blood flow and pressure through its influence on smooth muscle tone.

Pharmacokinetics

Carbon dioxide is produced endogenously during metabolic processes and is transported in the bloodstream primarily in three forms: dissolved in plasma, as bicarbonate ions (HCO3-), and bound to hemoglobin. The half-life of CO2 in the bloodstream is very short due to its rapid exchange with alveolar gas in the lungs. The elimination of CO2 occurs through exhalation, making it a dynamic component of respiratory physiology.

Pregnancy

Data on the effects of dioxide during pregnancy are limited. Caution is advised due to potential risks associated with exposure.

Breast-feeding

Limited data are available regarding the excretion of dioxide in human milk. Caution is recommended.

Storage

Store in a cool, dry place, away from direct sunlight and moisture.

Indications

• Electrolyte replacement
• Volume expansion in hypovolemic patients
• Management of hyponatremia
• Support in intravenous fluid therapy

Dosage

Children: Refer to the BNF for Children for appropriate dosing in paediatric patients, as dosages may vary based on the formulation and clinical condition.

Adults: Refer to specific product information or clinical guidelines for dosage recommendations, as disodium is often part of combination products.

Mechanism of action

Disodium compounds often function by providing sodium ions that are essential for various physiological processes. Sodium ions play a critical role in maintaining osmotic balance, nerve impulse transmission, and muscle contraction. In the context of intravenous solutions, disodium helps to restore electrolyte balance in patients.

Pharmacodynamics

The pharmacodynamics of disodium is primarily related to its role in electrolyte balance and fluid homeostasis. Sodium ions are vital for the function of excitable tissues, including neurons and muscle cells. Changes in sodium levels can affect blood pressure, hydration status, and overall cellular function.

Pharmacokinetics

The pharmacokinetics of disodium compounds depend on their specific formulation and route of administration. When administered intravenously, disodium is rapidly distributed in the extracellular fluid, where it helps to maintain osmotic pressure. Sodium is primarily excreted by the kidneys, and its levels can be influenced by fluid intake, dietary sodium, and renal function.

Pregnancy

Use with caution. Consult a healthcare provider for specific guidance.

Breast-feeding

Use with caution. Consult a healthcare provider for specific guidance.

Storage

Store at room temperature, away from moisture and direct sunlight.

Indications

• Lead poisoning
• Zinc toxicity
• Cadmium poisoning
• Iron overload disorders

Dosage

Adults: Refer to the BNF for specific dosing recommendations for adults, as it may vary based on the condition being treated and the severity of metal poisoning.

Mechanism of action

The pharmacologic effects of edetate calcium disodium are due to the formation of chelates with divalent and trivalent metals. A stable chelate forms with any metal that can displace calcium from the molecule, which includes lead, zinc, cadmium, and iron. The excretion of zinc is significantly increased, while the effect on calcium excretion is minimal. The chelation process helps to reduce the toxicity of heavy metals in the body by promoting their urinary excretion.

Pharmacodynamics

Edetate calcium acts as a heavy metal chelating agent, forming stable, water-soluble complexes with metal ions that can be excreted in urine. One gram of edetate calcium can theoretically bind up to 620 mg of lead, though actual urinary excretion rates are lower, with approximately 5 mg of lead excreted per gram of EDTA in lead-poisoned patients. It is relatively ineffective against mercury, gold, or arsenic poisoning but can mobilize and eliminate zinc, cadmium, copper, iron, and manganese.

Pharmacokinetics

After intravenous administration, edetate calcium disodium is rapidly distributed in the blood and has a half-life that can vary based on the patient's condition and the presence of heavy metals. The drug is primarily excreted unchanged in the urine. Calcium levels may be transiently lowered during infusion, but significant mobilization of body calcium stores is usually not observed unless very slow infusions are administered. The effects on metal ion excretion are dose-dependent and vary according to the specific metal involved.

Contra-indications

• Hypersensitivity to edetate calcium disodium or any component of the formulation
• Pre-existing renal impairment
• Calcium deficiency states

Adverse effects

• Hypocalcemia
• Renal impairment
• Gastrointestinal disturbances such as nausea and vomiting
• Headache
• Hypotension
• Electrolyte imbalances

Interactions

• Increased risk of toxicity when used with nephrotoxic agents
• May interfere with the absorption of certain minerals and vitamins
• Should not be mixed with other intravenous drugs due to potential chemical interactions

Precautions

• Monitor renal function during treatment
• Use caution in patients with cardiovascular disease due to potential hypotensive effects
• Evaluate calcium levels periodically in patients receiving prolonged therapy
• Use with caution in patients with a history of seizures

Pregnancy

Limited data available on the use of edetate calcium disodium in pregnant women. Use only if clearly needed.

Breast-feeding

It is not known whether edetate calcium disodium is excreted in human milk. Caution is advised.

Storage

Store at room temperature, away from light and moisture. Keep out of reach of children.

Formulations

• Edetate calcium disodium injection

Indications

• Aromatherapy
• Anxiety relief
• Mood enhancement
• Antimicrobial applications
• Pain management
• Anti-inflammatory treatments

Dosage

Children: Dosage for paediatric use of essences should be approached with caution and tailored to the child's age, weight, and condition. Refer to specific pediatric guidelines or consult a healthcare provider for appropriate dosing information.

Adults: Dosage for essences varies widely based on the specific type of essence and the intended use. It is essential to refer to specific guidelines or consult a healthcare provider for appropriate dosing information.

Mechanism of action

The mechanism of action of essences can vary depending on the specific substance in question. Generally, essential oils and herbal extracts act through a combination of phytochemical interactions, influencing neurotransmitter systems, modulating inflammation, and exhibiting antimicrobial properties. These compounds may interact with various receptors in the body, including G-protein coupled receptors and ion channels, leading to physiological responses.

Pharmacodynamics

Pharmacodynamics of essences is largely dependent on their chemical composition. Many essential oils contain terpenes, phenols, and other bioactive compounds that exhibit a range of effects such as antibacterial, antifungal, anti-inflammatory, and analgesic properties. The effects can vary based on concentration, route of administration, and individual patient factors, influencing their efficacy and safety.

Pharmacokinetics

The pharmacokinetics of essences involves absorption, distribution, metabolism, and excretion. Essential oils are typically absorbed through the skin or via inhalation and can be distributed throughout the body via the bloodstream. They are often metabolized by the liver, with various pathways leading to the formation of active or inactive metabolites. Excretion mostly occurs through urine, but some components may also be eliminated through bile or exhalation.

Pregnancy

The safety of essence during pregnancy has not been established. Consultation with a healthcare provider is recommended before use.

Breast-feeding

It is unclear whether essence is excreted in breast milk. Caution is advised, and it is best to consult a healthcare provider.

Storage

Store in a cool, dry place away from direct sunlight. Keep out of reach of children.

Dosage

Children: Refer to the BNF for Children for appropriate dosing information in paediatric cases, especially in instances of overdose.

Adults: Refer to the BNF for specific dosing information based on clinical circumstances, particularly in cases of overdose.

Mechanism of action

Ethylene glycol is metabolized by alcohol dehydrogenase to glycoaldehyde, which is subsequently converted to glycolic, glyoxylic, and oxalic acids. These metabolites contribute to anion gap metabolic acidosis and are responsible for tissue injury through the formation of insoluble calcium oxalate crystals.

Pharmacodynamics

The toxicity of ethylene glycol arises from its metabolites, particularly glycolic and oxalic acids. These compounds induce metabolic acidosis, lead to renal failure through calcium oxalate crystal deposition in the kidneys, and can cause neurological impairment. The anion gap increases due to the accumulation of these acids, leading to complications such as cardiovascular instability and potential multi-organ failure.

Pharmacokinetics

Ethylene glycol is rapidly absorbed after oral ingestion. It undergoes first-pass metabolism primarily in the liver, where it is converted into its toxic metabolites. The elimination half-life of ethylene glycol varies but is generally prolonged in cases of renal impairment. Renal excretion of metabolites contributes to the duration of toxicity, necessitating prompt medical intervention in cases of overdose.

Adverse effects

• Metabolic acidosis
• Renal failure
• CNS depression
• Hypocalcemia
• Cardiovascular collapse
• Pulmonary edema

Precautions

• Use with caution in patients with renal impairment
• Monitor for signs of metabolic acidosis
• Evaluate electrolyte levels, particularly calcium

Pregnancy

There is limited data on the safety of ethylene glycol in pregnancy. It should only be used if clearly needed.

Breast-feeding

It is unknown if ethylene glycol is excreted in human milk. Caution is advised.

Storage

Store in a tightly closed container at room temperature, away from heat and moisture.

Formulations

• Liquid

Indications

• Insecticide for agricultural use
• Research tool in toxicology

Dosage

Children: Refer to the BNF for Children for specific dosing and administration guidelines.

Adults: Refer to the BNF for specific dosing and administration guidelines.

Mechanism of action

Methyl parathion acts primarily by inhibiting the enzyme acetylcholinesterase, which is essential for the breakdown of the neurotransmitter acetylcholine. Its active metabolite, methyl paraoxon, is a potent inhibitor of both acetylcholinesterase and butyrylcholinesterase. The inhibition of these enzymes results in the accumulation of acetylcholine at synapses, leading to overstimulation of cholinergic receptors and resultant toxic effects.

Pharmacodynamics

The pharmacodynamics of methyl parathion involve its action as a noncompetitive inhibitor of acetylcholinesterase, causing prolonged effects of acetylcholine due to its inability to be hydrolyzed. The resultant cholinergic toxicity can lead to symptoms such as muscle twitching, respiratory distress, and potentially fatal outcomes if not treated promptly. The extent of inhibition is dose-dependent, with significant toxicity occurring after substantial enzyme inhibition.

Pharmacokinetics

Methyl parathion is absorbed through the gastrointestinal tract and can also be absorbed through the skin and respiratory tract. It is metabolized in the liver to form methyl paraoxon, which is responsible for the majority of its toxic effects. The distribution of methyl parathion in body tissues is influenced by its lipophilicity, and it is primarily excreted as metabolites in the urine. The elimination half-life and specific pharmacokinetic parameters can vary based on individual metabolism and exposure levels.

Pregnancy

There are no adequate and well-controlled studies in pregnant women. Use only if the potential benefit justifies the potential risk to the fetus.

Breast-feeding

It is not known whether this drug is excreted in human milk. Caution is advised when administering to nursing women.

Storage

Store in a cool, dry place away from direct sunlight. Keep out of reach of children.

Formulations

• Liquid formulation

Indications

• Allergic conditions
• Autoimmune diseases
• Asthma and chronic obstructive pulmonary disease (COPD)
• Certain cancers (e.g., leukemia, lymphoma)
• Skin conditions (e.g., dermatitis)
• Inflammatory bowel disease
• Multiple sclerosis exacerbations
• Severe infections requiring immunosuppression

Dosage

Children: Refer to BNF for Children for specific dosing; doses vary significantly based on the child's age, weight, and condition being treated.

Adults: Refer to BNF for specific dosing; typically, initial doses range from 4 to 48 mg depending on the severity of the condition.

Mechanism of action

Methylprednisolone exerts its effects by binding to glucocorticoid receptors, leading to the modulation of gene expression. This interaction influences the transcription of anti-inflammatory proteins while suppressing the expression of pro-inflammatory genes, ultimately resulting in reduced inflammation and immune response.

Pharmacodynamics

The pharmacodynamic effects of methylprednisolone are characterized by its ability to decrease inflammation, suppress the immune response, and affect carbohydrate metabolism. Therapeutic doses lead to various systemic effects, including modification of leukocyte distribution and inhibition of cytokine production.

Pharmacokinetics

Methylprednisolone is well absorbed after oral administration, with a bioavailability of approximately 50%. It has a volume of distribution that reflects extensive tissue binding. The drug is metabolized primarily in the liver through conjugation and reduction, and its metabolites are excreted in urine. The half-life varies based on the route of administration but is generally around 18 to 36 hours.

Adverse effects

• Increased blood pressure
• Hyperglycemia
• Weight gain
• Mood changes
• Insomnia
• Gastrointestinal disturbances
• Increased susceptibility to infections

Interactions

• methylphenidate+apraclonidine: Severe (decreases effects)
• methylthioninium chloride+bupropion: Severe (increases risk of severe hypertension)
• methylphenidate+linezolid: Severe (increases risk of elevated blood pressure)
• rasagiline+methylphenidate: Severe (increases risk of a hypertensive crisis)
• mao-inhibitors+methylphenidate: Severe (increases risk of a hypertensive crisis)
• dronedarone+methylprednisolone: Moderate (increases exposure)
• miconazole+methylprednisolone: Moderate (increases concentration)
• antifungals, azoles+methylprednisolone: Moderate (increases exposure)
• crizotinib+methylprednisolone: Moderate (increases exposure)

Precautions

• Use with caution in patients with hypertension
• Monitor blood glucose levels in diabetic patients
• Consider potential for infection risk due to immunosuppression
• Evaluate for psychiatric effects in susceptible individuals

Pregnancy

Corticosteroids may be used during pregnancy if the potential benefit justifies the risk to the fetus. Careful monitoring is advised.

Breast-feeding

Corticosteroids are excreted in breast milk; caution is advised. Monitor the infant for potential effects.

Storage

Store in a cool, dry place, away from light. Keep out of reach of children.

Formulations

• Tablets
• Injectable solutions
• Topical preparations

Mechanism of action

Methylsulphate functions as a methylating agent, transferring a methyl group to nucleophiles. This process involves the formation of a sulfonium ion, which is highly reactive and can readily react with nucleophilic sites on various substrates, leading to methylation reactions.

Pharmacodynamics

The pharmacodynamics of methylsulphate is primarily related to its role as a methylating agent in biochemical reactions. It can alter the structure and function of biological molecules, potentially affecting cellular processes and signaling pathways. However, detailed pharmacodynamic studies specific to therapeutic use are limited.

Pharmacokinetics

There is limited information on the pharmacokinetics of methylsulphate, given its typical use as a reagent in laboratory settings rather than a clinical drug. When used in chemical reactions, its reactivity and transformation into other compounds would dictate its pharmacokinetic profile, which could vary significantly based on the specific context of use.

Pregnancy

There is limited data on the use of methylsulphate in pregnancy. Consult relevant guidelines.

Breast-feeding

Data on the excretion of methylsulphate in human milk is not available. Caution is advised.

Storage

Store in a cool, dry place, away from direct sunlight.

Indications

• Preservative in cosmetics
• Preservative in pharmaceuticals
• Preservative in food products

Dosage

Children: Refer to specific product guidelines as dosing varies based on formulation and concentration used.

Adults: Refer to specific product guidelines as dosing varies based on formulation and concentration used.

Mechanism of action

Parabens work by inhibiting the growth of microorganisms through their ability to disrupt the cellular processes of bacteria and fungi. They penetrate the microbial cell membrane and disrupt enzyme and protein functions, leading to cell death. Parabens are known to have low toxicity and are metabolized by the body, subsequently being excreted in urine.

Pharmacodynamics

Parabens demonstrate broad-spectrum antimicrobial activity, making them effective preservatives in various formulations. Their efficacy is influenced by factors such as concentration, pH, and the presence of other ingredients in the formulation. Due to their structural similarity to estrogen, there has been concern regarding their potential endocrine-disrupting effects, although the clinical significance of this is still debated.

Pharmacokinetics

Parabens are readily absorbed through the skin and gastrointestinal tract. Once absorbed, they are rapidly metabolized primarily in the liver. They undergo hydrolysis to form para-hydroxybenzoic acid, which is then conjugated with glucuronic acid and excreted in urine. The half-life of parabens in the human body is relatively short, and they are eliminated rapidly.

Adverse effects

• Allergic reactions, such as skin rashes
• Irritation at the site of application
• Endocrine disruption (in high concentrations)

Precautions

• Use with caution in individuals with known sensitivities or allergies to parabens
• Consider potential endocrine effects with prolonged exposure

Pregnancy

Parabens are generally considered safe in cosmetics and personal care products during pregnancy, although caution is advised due to potential endocrine disruption.

Breast-feeding

Parabens are considered safe in breastfeeding, but it is recommended to use products with minimal or no parabens when possible.

Storage

Store in a cool, dry place away from direct sunlight. Keep out of reach of children.

Formulations

• Topical creams
• Lotions
• Shampoos
• Conditioners
• Makeup products
• Pharmaceutical preparations

Indications

• Irritable bowel syndrome
• Dyspepsia
• Nausea
• Headaches
• Respiratory congestion

Dosage

Children: Refer to the BNF for Children for appropriate dosing guidelines.

Adults: Refer to the relevant product-specific information for dosing recommendations, as peppermint formulations can vary widely.

Mechanism of action

The primary active component, menthol, works by activating the TRPM8 (transient receptor potential cation channel subfamily M member 8) ion channel, which is involved in the sensation of cold and cooling. This action can lead to a localized anesthetic effect, reducing pain and discomfort. Additionally, menthol can cause relaxation of smooth muscle in the gastrointestinal tract, aiding in the relief of digestive symptoms.

Pharmacodynamics

Peppermint exhibits antispasmodic effects, particularly in the gastrointestinal tract, by relaxing the smooth muscles. It also has a mild analgesic effect due to its cooling sensation, which can provide symptomatic relief in various conditions. Furthermore, peppermint oil may have antimicrobial properties, contributing to its use in treating certain infections.

Pharmacokinetics

Menthol is rapidly absorbed after oral administration and is metabolized in the liver. The peak plasma concentration typically occurs within a few hours. The elimination half-life of menthol is approximately 1.5 to 2 hours, and it is primarily excreted in the urine as metabolites. The pharmacokinetics of peppermint oil can vary based on the formulation and route of administration.

Interactions

• peppermint oil + lomitapide: Unknown (increases exposure)

Pregnancy

Peppermint is generally considered safe for use in pregnancy when used in culinary amounts. However, high doses should be avoided due to potential uterine stimulation.

Breast-feeding

Peppermint is considered safe during breastfeeding when used in culinary amounts. Caution is advised with high doses as effects on the infant are not well studied.

Storage

Store in a cool, dry place away from direct sunlight. Keep out of reach of children.

Formulations

• Peppermint oil
• Peppermint extract
• Peppermint tea

Indications

• Dehydration
• Hyponatremia
• Heat-related illnesses
• Kidney function maintenance
• Electrolyte balance

Dosage

Children: For children, the amount of potable water required varies by age, size, and activity level. It is important to ensure adequate hydration, particularly in hot weather or during physical activity. Refer to BNF for Children for specific guidance.

Adults: General guidance for adults is to consume an adequate amount of water daily, typically around 2-3 liters, but this can vary based on individual needs and activity levels. Specific dosing should be based on hydration requirements.

Mechanism of action

Potable water does not have a specific pharmacological mechanism of action as it is not a drug. However, it facilitates numerous biological functions in the body, including nutrient transport, temperature regulation, and waste elimination. The presence of soluble minerals and electrolytes in water can also aid in maintaining homeostasis.

Pharmacodynamics

The pharmacodynamics of potable water can be understood in terms of its role in maintaining fluid balance, supporting cellular functions, and aiding in metabolic processes. Adequate hydration is crucial for maintaining blood volume, regulating body temperature, and ensuring proper kidney function. The body's response to hydration status involves hormonal regulation, including the release of antidiuretic hormone (ADH) to manage water retention.

Pharmacokinetics

As a substance that is ingested, potable water is quickly absorbed in the gastrointestinal tract. The rate of absorption can vary based on factors such as temperature, the presence of electrolytes, and individual physiological conditions. Once absorbed, water is distributed throughout the body, where it enters cells and is involved in various metabolic processes. The renal system plays a significant role in regulating water balance through filtration and reabsorption.

Pregnancy

The safety of potable water is critical during pregnancy. Contaminated water can lead to infections and complications. It is essential to ensure that drinking water is safe.

Breast-feeding

Mothers should ensure access to safe drinking water to prevent transmission of waterborne diseases to infants through contaminated sources.

Storage

Potable water should be stored in clean, food-grade containers, away from direct sunlight and contaminants. Ensure containers are regularly cleaned.

Indications

• Hyperthyroidism
• Graves' disease
• Thyroid storm

Dosage

Children: Refer to the BNF

Adults: The usual initial dose of propylthiouracil in adults is 300 mg per day, divided into 3 doses. The maintenance dose is typically 100-150 mg per day, adjusted based on thyroid function tests.

Mechanism of action

Propylthiouracil acts by inhibiting the enzyme thyroid peroxidase, which is involved in the iodination of tyrosine residues in thyroglobulin, a precursor of thyroid hormones. By blocking this enzyme, PTU reduces the production of thyroxine (T4) and triiodothyronine (T3), leading to decreased thyroid hormone levels in circulation. Additionally, PTU inhibits the conversion of T4 to T3 in peripheral tissues, further contributing to its antithyroid effects.

Pharmacodynamics

The pharmacodynamic effects of propylthiouracil are primarily centered around its ability to lower thyroid hormone levels, which helps alleviate symptoms of hyperthyroidism such as increased heart rate, weight loss, and anxiety. The onset of action can vary, but therapeutic effects may be observed within several weeks of initiation. Monitoring thyroid function tests is essential to assess the efficacy and adjust dosing as needed.

Pharmacokinetics

Propylthiouracil is well absorbed from the gastrointestinal tract, though its bioavailability can be affected by factors such as food intake. The drug is extensively metabolized in the liver, and its elimination half-life averages around 1-2 hours. Most of the drug is excreted in urine as metabolites. It is important to note that due to its rapid metabolism, multiple daily doses may be required to maintain therapeutic levels.

Interactions

• propylthiouracil+metyrapone: Severe (decreases effects)

Indications

• Used as a solvent for drug formulations
• Serves as a humectant in topical medications
• Acts as a preservative in various pharmaceutical preparations

Dosage

Children: Refer to specific formulations and product guidelines for appropriate dosing, as dosages vary depending on the formulation and intended use.

Adults: Refer to specific formulations and product guidelines for appropriate dosing, as dosages vary depending on the formulation and intended use.

Mechanism of action

Propylen acts as a humectant by attracting and retaining moisture. It helps to solubilize other compounds and enhances the bioavailability of certain drugs by improving their solubility in aqueous solutions. Propylen glycol also serves as a vehicle for drug delivery, facilitating the absorption of active pharmaceutical ingredients.

Pharmacodynamics

Propylen has minimal pharmacodynamic effects on its own, as it primarily acts as an excipient. Its role in formulations allows for improved stability and efficacy of active ingredients. The pharmacodynamic properties of the drug in which propylen is used will depend on the active compounds it is combined with.

Pharmacokinetics

Propylen is rapidly absorbed following oral or parenteral administration. It is distributed widely throughout the body, with a volume of distribution of approximately 0.5 to 0.7 L/kg. Propylen is metabolized in the liver to lactic acid and other metabolites, which are then eliminated through the kidneys. The elimination half-life is variable, generally ranging from a few hours to half a day, depending on individual metabolic rates.

Pregnancy

Safety during pregnancy has not been established. Use only if clearly needed.

Breast-feeding

Use with caution. Consult healthcare provider.

Storage

Store at room temperature, away from moisture and heat.

Indications

• Potential role in bone health
• Support for connective tissue formation
• May aid in mineral metabolism

Dosage

Children: There is no established clinical dosage for silicon in paediatric populations, as it is not classified as an essential nutrient.

Adults: There is no established clinical dosage for silicon in adults, as it is not classified as an essential nutrient.

Mechanism of action

Silicon is believed to enhance the synthesis of glycosaminoglycans and collagen, which are important for the structural integrity of connective tissues. It may also influence the activity of certain enzymes involved in bone mineralization, thus playing a role in maintaining bone density and health.

Pharmacodynamics

The pharmacodynamics of silicon is not fully elucidated; however, it is thought to involve the modulation of bone metabolism and the promotion of connective tissue health. Silicon may have a synergistic effect with other minerals, such as calcium and magnesium, aiding in their utilization and metabolism in the body.

Pharmacokinetics

The pharmacokinetics of silicon is complex, as it is not absorbed through typical gastrointestinal pathways. Instead, silicon is thought to be taken up in the form of silicates and then distributed throughout the body, particularly in connective tissues. The elimination of silicon occurs primarily through renal excretion, with some variations depending on dietary intake and individual metabolism.

Pregnancy

Silicon is generally considered safe during pregnancy, as it is a naturally occurring element in the human body. However, specific recommendations regarding supplementation should be followed based on the advice of a healthcare provider.

Breast-feeding

Silicon is present in breast milk in small amounts. Its safety during breastfeeding is generally regarded as acceptable, although supplementation should be approached with caution and under medical advice.

Storage

Silicon should be stored in a cool, dry place, protected from light and moisture. Follow specific storage recommendations provided by the manufacturer if available.

Indications

• Food preservation
• Cosmetic preservation
• Pharmaceutical preservation

Dosage

Children: Refer to applicable regulations and guidelines for specific usage limits, typically not exceeding 0.1% to 0.3% in food products.

Adults: Refer to applicable regulations and guidelines for specific usage limits, typically not exceeding 0.1% to 0.3% in food products.

Mechanism of action

Sorbic acid exerts its antimicrobial effects by inhibiting the enzyme activity required for yeast and mold growth. It disrupts the metabolic pathways of these microorganisms, preventing their reproduction and leading to cell death. The undissociated form of sorbic acid penetrates the microbial cell membrane, where it lowers the intracellular pH, thus inhibiting vital cellular processes.

Pharmacodynamics

Sorbic acid is effective against a wide range of fungi and some bacteria. Its antimicrobial activity is pH-dependent, exhibiting greater efficacy at lower pH levels. The compound is particularly effective in acidic environments, making it suitable for use in acidic food products. The inhibitory concentration varies depending on the type of microorganism, with molds generally being more susceptible than bacteria.

Pharmacokinetics

Sorbic acid is poorly absorbed in the gastrointestinal tract when ingested, leading to minimal systemic exposure. It is primarily excreted unchanged in the urine. The half-life of sorbic acid in the body is short, which correlates with its rapid elimination. The compound does not accumulate in tissues, making it safe for short-term consumption at low doses.

Adverse effects

• Allergic reactions
• Skin irritation
• Gastrointestinal disturbances

Precautions

• Use with caution in patients with known allergies to sorbates
• Should be used in moderation to avoid potential gastrointestinal upset

Pregnancy

Safety during pregnancy has not been established; consult a healthcare provider before use.

Breast-feeding

Consult a healthcare provider before use while breastfeeding.

Storage

Store in a cool, dry place, away from direct sunlight. Keep out of reach of children.

Formulations

• Sorbic acid
• Potassium sorbate

Indications

• Providing energy in dietary supplementation
• Enhancing flavor in food products
• Replacement of carbohydrates in certain medical nutrition therapies

Dosage

Children: Refer to general dietary guidelines for carbohydrate intake in children. No specific dosing guidelines provided.

Adults: Refer to general dietary guidelines for carbohydrate intake. No specific dosing guidelines provided.

Mechanism of action

Sugar is metabolized in the body to provide energy. Upon ingestion, sucrose is broken down by the enzyme sucrase into its constituent monosaccharides, glucose and fructose, which are then absorbed into the bloodstream. These monosaccharides can be utilized by cells for energy or stored as glycogen in the liver and muscles.

Pharmacodynamics

As a simple carbohydrate, sugar elevates blood glucose levels rapidly after consumption, leading to increased insulin secretion from the pancreas. This insulin facilitates the uptake of glucose by tissues, promoting energy production. The rapid increase in blood sugar can provide quick energy but may also lead to potential negative effects on metabolism and weight if consumed in excess.

Pharmacokinetics

After oral administration, sugar is quickly hydrolyzed in the gastrointestinal tract. Peak plasma glucose concentrations typically occur within 30 minutes to 2 hours post-ingestion, depending on the amount consumed and individual metabolism. The half-life of glucose in the bloodstream is relatively short, as it is rapidly taken up by tissues or converted into glycogen.

Pregnancy

Sugar is generally considered safe for use during pregnancy, but excessive intake should be avoided to prevent gestational diabetes and excessive weight gain.

Breast-feeding

Sugar is safe during breastfeeding; however, excessive consumption should be avoided.

Storage

Store in a cool, dry place, away from moisture and direct sunlight.

Formulations

• Granulated sugar
• Brown sugar
• Powdered sugar
• Liquid sugar

Indications

• Urinary tract infections
• Respiratory tract infections
• Gastrointestinal infections
• Pneumocystis pneumonia
• Toxoplasmosis

Dosage

Children: Refer to the BNF for Children for specific dosing information appropriate for paediatric patients, as doses are typically weight-based and vary by age and condition.

Adults: Refer to the BNF for specific dosing information based on the clinical condition being treated, as dosing may vary depending on the severity of the infection and patient characteristics.

Mechanism of action

Sulfamethoxazole inhibits bacterial dihydrofolic acid synthesis due to its structural similarity to para-aminobenzoic acid (PABA). It competitively inhibits dihydropteroate synthase, the enzyme responsible for converting PABA to dihydrofolic acid. This action prevents the synthesis of tetrahydrofolate, leading to the inhibition of bacterial purine and DNA synthesis, resulting in a bacteriostatic effect.

Pharmacodynamics

Sulfamethoxazole is generally bacteriostatic, inhibiting a crucial step in bacterial folate synthesis. It is typically used in combination with trimethoprim, which inhibits the reduction of dihydrofolic acid to tetrahydrofolate. This combination allows for a synergistic effect, reducing the rate of bacterial resistance development compared to using either drug alone. Care should be taken as sulfamethoxazole can cause hypersensitivity reactions, and it may contribute to folate deficiency, particularly in at-risk populations.

Pharmacokinetics

Sulfamethoxazole is well absorbed following oral administration and is widely distributed in body tissues. It has a moderate half-life, necessitating multiple daily doses for sustained therapeutic effect. The drug is metabolized in the liver and excreted primarily via the kidneys, with some metabolites being active. Its excretion can be influenced by renal function, necessitating dose adjustments in patients with compromised kidney function.

Contra-indications

• Hypersensitivity to sulfamethoxazole or other sulfonamides
• Severe liver impairment
• Severe renal impairment
• History of severe adverse reactions to sulfonamides (e.g., Stevens-Johnson syndrome)

Adverse effects

• Rash
• Nausea
• Vomiting
• Diarrhea
• Hematological reactions (e.g., leukopenia, thrombocytopenia)
• Liver toxicity
• Renal toxicity
• Hemolytic anemia in patients with G6PD deficiency
• Stevens-Johnson syndrome
• Toxic epidermal necrolysis

Interactions

• Sulfamethoxazole may increase the anticoagulant effect of coumarins
• Concurrent use with other folate antagonists may enhance toxicity
• May interact with methotrexate, increasing the risk of toxicity

Precautions

• Use with caution in patients with a history of hypersensitivity reactions
• Monitor for signs of folate deficiency
• Assess renal and liver function prior to and during treatment
• Discontinue immediately at the first sign of rash or skin reaction

Pregnancy

Sulfamethoxazole is generally not recommended during pregnancy, especially in the first trimester and near term, due to potential risks of teratogenic effects and kernicterus in the newborn.

Breast-feeding

Sulfamethoxazole is excreted in breast milk; caution is advised when administering to nursing mothers due to potential effects on the nursing infant.

Storage

Store at room temperature, away from moisture and heat. Protect from light.

Formulations

• Oral tablets
• Oral suspension
• Injection

Indications

• Used as an emulsifier in pharmaceutical formulations
• Improving the solubility of poorly soluble drugs
• Stabilizing emulsions in topical and oral medications
• Used in laboratory settings as a surfactant

Dosage

Children: Dosage varies based on formulation and intended use, refer to specific product guidelines.

Adults: Dosage varies based on formulation and intended use, refer to specific product guidelines.

Mechanism of action

Tween works by reducing the surface tension of the liquid it is mixed with, allowing for better mixing of hydrophilic and hydrophobic substances. This property makes it effective in enhancing the delivery of drugs that are poorly soluble in water. Tween can also stabilize emulsions by forming a protective layer around droplets, preventing them from coalescing.

Pharmacodynamics

As a surfactant, Tween enhances the solubility of lipophilic compounds and improves the absorption of drugs through biological membranes. Its application in drug formulation can lead to increased bioavailability and improved therapeutic effects, especially for poorly soluble drugs.

Pharmacokinetics

Tween is generally not absorbed significantly in the gastrointestinal tract when ingested. Instead, it has a local effect in the gastrointestinal tract and may influence the absorption of other compounds. The metabolism of Tween is not well characterized, and its excretion primarily occurs through feces. The overall pharmacokinetic profile is influenced by the specific formulation in which it is used.

Pregnancy

Tween (polysorbate 20) is generally considered safe for use during pregnancy. However, it should be used only when clearly needed and after consultation with a healthcare provider.

Breast-feeding

Tween is considered safe for use during breastfeeding. Its absorption and systemic exposure are minimal, but it is advisable to consult a healthcare provider.

Storage

Store at room temperature, away from moisture and heat. Keep tightly closed in a cool, dry place.

Mechanism of action

Trimethoprim is a reversible inhibitor of dihydrofolate reductase, one of the principal enzymes catalyzing the formation of tetrahydrofolic acid (THF) from dihydrofolic acid (DHF). Tetrahydrofolic acid is necessary for the biosynthesis of bacterial nucleic acids and proteins and ultimately for continued bacterial survival - inhibiting its synthesis, then, results in bactericidal activity. Trimethoprim binds with a much stronger affinity to bacterial dihydrofolate reductase as compared to its mammalian counterpart, allowing trimethoprim to selectively interfere with bacterial biosynthetic processes. Trimethoprim is often given in combination with sulfamethoxazole, which inhibits the preceding step in bacterial protein synthesis - given together, sulfamethoxazole and trimethoprim inhibit two consecutive steps in the biosynthesis of bacterial nucleic acids and proteins. As a monotherapy trimethoprim is considered bacteriostatic, but in combination with sulfamethoxazole is thought to exert bactericidal activity. Trimethoprim is a bacteriostatic lipophilic weak base structurally related to pyrimethamine. It binds to and reversibly inhibits the bacterial enzyme dihydrofolate reductase, selectively blocking conversion of dihydrofolic acid to its functional form, tetrahydrofolic acid. This depletes folate, an essential cofactor in the biosynthesis of nucleic acids, resulting in interference with bacterial nucleic acid and protein production. Bacterial dihydrofolate reductase is approximately 50,000 to 60,000 times more tightly bound by trimethoprim than is the corresponding mammalian enzyme. To determine the incidence & severity of hyperkalemia during trimethoprim therapy, 30 consecutive patients with acquired immunodeficiency syndrome receiving high-dose (20 mg/kg/day) trimethoprim were studied; in addition, the mechanism of trimethoprim-induced hyperkalemia was investigated in rats. Trimethoprim increased serum potassium concn by 0.6 mmol/l despite normal adrenocortical function & glomerular filtration rate. Serum potassium levels >5 mmol/l were observed during trimethoprim treatment in 15 of 30 patients. In rats, iv trimethoprim inhibited renal potassium excretion by 40% & increased sodium excretion by 46%. It was concluded that trimethoprim blocks apical membrane sodium channels in the mammalian distal nephron. As a consequence, the transepithelial voltage is reduced & potassium secretion is inhibited. Decreased renal potassium excretion secondary to these direct effects on kidney tubules leads to hyperkalemia in a substantial number of patients being treated with trimethoprim-containing drugs.

Pharmacodynamics

Trimethoprim exerts its antimicrobial effects by inhibiting an essential step in the synthesis of bacterial nucleic acids and proteins. It has shown activity against several species of gram-negative bacteria, as well as coagulase-negative _Staphylococcus_ species. Resistance to trimethoprim may arise via a variety of mechanisms, including alterations to the bacterial cell wall, overproduction of dihydrofolate reductase, or production of resistant dihydrofolate reductase. Rarely, trimethoprim can precipitate the development of blood disorders (e.g. thrombocytopenia, leukopenia, etc.) which may be preceded by symptoms such as sore throat, fever, pallor, and or purpura - patients should be monitored closely for the development of these symptoms throught the course of therapy. As antimicrobial susceptibility patterns are geographically distinct, local antibiograms should be consulted to ensure adequate coverage of relevant pathogens prior to use.

Mechanism of action

The pharmacologic effects of edetate calcium disodium are due to the formation of chelates with divalent and trivalent metals. A stable chelate will form with any metal that has the ability to displace calcium from the molecule, a feature shared by lead, zinc, cadmium, manganese, iron and mercury. The amounts of manganese and iron metabolized are not significant. Copper is not mobilized and mercury is unavailable for chelation because it is too tightly bound to body ligands or it is stored in inaccessible body compartments. The excretion of calcium by the body is not increased following intravenous administration of edetate calcium disodium, but the excretion of zinc is considerably increased. Effects on rat liver glucocorticoid receptor in vitro was studied. At 4 °C, 10 mmole EDTA had a stablizing effect on unbound hepatic glucocorticoid receptors. Apparently, endogenous metal ions are involved in the processes of glucocorticoid-receptor complex stabilization and transformation. Edetate disodium injection forms chelates with the cations of calcium and many divalent and trivalent metals. Because of its affinity for calcium, edetate disodium will produce a lowering of the serum calcium level during intravenous infusion. Slow infusion over a protracted period may cause mobilization of extracirculatory calcium stores. Edetate disodium exerts a negative inotropic effect upon the heart. Edetate disodium likewise forms chelates with other polyvalent metals and produces increases in urinary excretion of magnesium, zinc and other trace elements. It does not form a chelate with potassium but may reduce the serum level and increase urinary loss of potassium.

Pharmacodynamics

Edetate calcium is a heavy metal chelating agent. The calcium in edetate calcium can be displaced by divalent or trivalent metals to form a stable water soluble complex that can be excreted in the urine. In theory, 1 g of edetate calcium can theoretically bind 620 mg of lead, but in reality only about 5 mg per gram is actually excreted into the urine in lead poisoned patients. In addition to chelating lead, edetate calcium also chelates and eliminates zinc from the body. Edetate calcium also binds cadmium, copper, iron and manganese, but to a much lesser extent than either lead or zinc. Edetate calcium is relatively ineffective for use in treating mercury, gold or arsenic poisoning.

Mechanism of action

Ethylene glycol is metabolized by alcohol dehydrogenase to glycoaldehyde, which is then metabolized to glycolic, glyoxylic, and oxalic acids. These acids, along with excess lactic acid are responsible for the anion gap metabolic acidosis. Oxalic acid readily precipitates with calcium to form insoluble calcium oxalate crystals. Tissue injury is caused by widespread deposition of oxalate crystals and the toxic effects of glycolic and glyoxylic acids.

Mechanism of action

Acute poisoning ... is related to ... inhibiting action on enzyme acetylcholinesterase. Toxic manifestations generally occur only after more than 50% of plasma cholinesterase is inhibited. ... Methyl parathion ... depend on oxidative activation by replacement of thiono-sulfur with oxygen for ... toxicity. Methyl parathion has only a slight inhibitory action on acetylcholinesterase and butyrylcholinesterase, but its active metabolite, methyl paraoxon, is a potent inhibitor of both these enzymes. A study was conducted examining the inhibition of (Ca2+ and Mg2+)-ATPase by parathion (56382) and methyl parathion. Enzyme activity was assessed spectrophotometrically in pig erythrocyte membranes containing calcium2+ (Ca2+) and magnesium2+ and in solubilized membrane preparations incubated with the test agents. The enzyme response to ATP was biphasic. Equations expressing the kinetics of the substrate curves described two classes of the ATP binding active site, one with high affinity and low maximum rate and one with low affinity and high maximum rate. High affinity active sites were stimulated by low ATP concentrations (20 uM), whereas low affinity active sites were stimulated by high ATP levels (2 mM). Parathion and methylparathion dose dependently inhibited enzyme activity; parathion had a greater inhibitory effect than methylparathion. Lineweaver-Burke and Dixon plots indicated noncompetitive inhibition. Parathion and methylparathion induced enzyme inhibition occurred over a range of free calcium ion concentrations (0.5 to 5 mM); the inhibition was significantly greater at lower Ca2+ concentrations (1 to 100 uM) than at higher concentrations. The authors conclude that parathion and methylparathion inhibit ATPase activity by binding to a site on the enzyme rather than through an interaction with associated lipids. For more Mechanism of Action (Complete) data for METHYL PARATHION (6 total), please visit the HSDB record page.

Mechanism of action

Sulfamethoxazole is a sulfonamide that inhibits bacterial dihydrofolic acid synthesis due to its structural similarity to an endogenous substrate, para-aminobenzoic acid (PABA). Most bacteria meet their need for folic acid by synthesizing it from PABA, as opposed to Animalia that require exogenous folic acid sources. Sulfamethoxazole competitively inhibits dihydropteroate synthase, the enzyme responsible for bacterial conversion of PABA to dihydrofolic acid. Inhibition of this pathway prevents the synthesis of tetrahydrofolate and, ultimately, the synthesis of bacterial purines and DNA, resulting in a bacteriostatic effect. Sulfonamides are usually bacteriostatic in action. Sulfonamides interfere with the utilization of p-aminobenzoic acid (PABA) in the biosynthesis of tetrahydrofolic acid (the reduced form of folic acid) cofactors in susceptible bacteria. Sulfonamides are structural analogs of PABA and appear to interfere with PABA utilization by competitively inhibiting the enzyme dihydropteroate synthase, which catalyzes the formation of dihydropteroic acid (a precursor of tetrahydrofolic acid) from PABA and pteridine; however, other mechanism(s) affecting the biosynthetic pathway also may be involved. Compounds such as pyrimethamine and trimethoprim, which block later stages in the synthesis of folic acid, act synergistically with sulfonamides. Only microorganisms that synthesize their own folic acid are inhibited by sulfonamides; animal cells and bacteria which are capable of utilizing folic acid precursors or preformed folic acid are not affected by these drugs. The antibacterial activity of the sulfonamides is reportedly decreased in the presence of blood or purulent body exudates. /Sulfonamides/ /Sulfonamides inhibit bacterial growth by preventing para-aminobenzoic acid (PABA) from being incorporated/ into dihydropteroic acid, the immediate precursor of folic acid. Sensitive microorganisms are those that must synthesize their own folic acid; bacteria that can utilize preformed folate are not affected. Bacteriostasis induced by sulfonamides is counteracted by PABA competitively. Sulfonamides do not affect mammalian cells by this mechanism, since they require preformed folic acid and cannot synthesize it. /Sulfonamides/ Sulfonamides are broad-spectrum, bacteriostatic anti-infectives. They are structural analogs of para-aminobenzoic acid and competively inhibit a bacterial enzyme, dihydropteroate synthetase, that is responsible for incorporation of para-aminobenzoic acid into dihydrofolic acid. This blocks the synthesis of dihydrofolic acid and decreases the amount of metabolically active tetrahydrofolic acid, a cofactor for the synthesis of purines, thymidine, and DNA. /Sulfonamides/ The hydroxylamine and nitroso metabolites formed by N4-oxidation of sulfonamides are thought to be involved in the pathogenesis of idiosyncratic reactions to this class of drugs. Idiosyncratic reactions to sulfonamides are characterized by multisystemic toxicity, including hepatitis, nephritis, dermatitis, and blood dyscrasias (aplastic anemia, agranulocytosis). Previously it has been shown that cytochrome p-450 in the liver metabolizes sulfamethoxazole to its hydroxylamine metabolite. In this paper the N4-oxidation of sulfamethoxazole by activated monocytes and neutrophils (human and canine) to form sulfamethoxazole hydroxylamine and nitrosulfamethoxazole is reported. The presumed nitroso intermediate was not detected. Purified myeloperoxidase and prostaglandin H synthase were also capable of mediating the oxidation of sulfamethoxazole. The present studies suggest that myeloperoxidase is responsible for the observed oxidation by phagocytic cells. Oxidation by neutrophils may play a role in agranulocytosis, and oxidation by monocytes may facilitate antigen presentation. Extrahepatic bioactivation of sulfonamides by peroxidases in phagocytic cells and other tissues may be important in determining the range of adverse reactions to sulfonamides

Pharmacodynamics

Sulfamethoxazole is a bacteriostatic sulfonamide antibiotic that inhibits a critical step in bacterial folate synthesis. It is generally given in combination with [trimethoprim], a dihydrofolate reductase inhibitor, which inhibits the reduction of dihydrofolic acid to tetrahydrofolic acid. Studies have shown that bacterial resistance develops more slowly with the combination of the two drugs than with either trimethoprim or sulfamethoxazole alone, as together they inhibit sequential steps in the bacterial folate synthesis pathway. Sulfonamides, including sulfamethoxazole, have been implicated in hypersensitivity reactions - these agents should be discontinued at the first sign of a developing rash, as this may signal the start of a more severe reaction such as Stevens-Johnson syndrome or toxic epidermal necrolysis. Sulfamethoxazole treatment may contribute to folate deficiency and should therefore be used with caution in patients at a higher risk of developing a deficiency. Hemolysis has been observed in patients with glucose-6-phosphate dehydrogenase deficiency who are using sulfamethoxazole/trimethoprim.