TETRAGEN

Indications

• Bacterial infections such as chlamydia
• Rickettsial infections
• Mycoplasma infections
• Acne vulgaris (off-label use)

Dosage

Children: In children aged 12 to 17 years, the recommended dose for susceptible infections is 100 mg daily, but this can vary based on specific circumstances and should be guided by the BNF for Children

Adults: For susceptible infections, the typical adult dose is 100 mg twice daily for 5 to 14 days, depending on the specific infection. For acne, 500 mg twice daily for 6 to 12 weeks may be used.

Mechanism of action

Tetracycline works by binding to the 30S ribosomal subunit of bacteria, inhibiting the attachment of aminoacyl-tRNA to the ribosomal acceptor site. This effectively prevents protein synthesis, which is essential for bacterial growth and replication.

Pharmacodynamics

The pharmacodynamics of tetracycline involves its bacteriostatic action, meaning it stops bacteria from multiplying rather than killing them outright. Its spectrum of activity covers a wide range of gram-positive and gram-negative bacteria, as well as some atypical pathogens. Resistance can develop through various mechanisms, including efflux pumps and ribosomal protection.

Pharmacokinetics

Tetracycline is well-absorbed from the gastrointestinal tract, although its absorption can be decreased by the presence of divalent and trivalent metal ions (such as calcium, magnesium, and iron). It is distributed widely in body tissues and fluids, with a volume of distribution of approximately 0.5-1.0 L/kg. Tetracycline is largely excreted unchanged in the urine, with a half-life ranging from 6 to 12 hours. Renal impairment can increase its half-life, necessitating caution in dosing.

Contra-indications

• Children under 12 years due to deposition in growing bone and teeth, causing staining and occasionally dental hypoplasia

Adverse effects

• Gastrointestinal disturbances
• Hearing impairment
• Discoloration of teeth
• Photosensitivity
• Dizziness
• Vertigo
• Skin reactions such as rash or pruritus
• Allergic reactions including anaphylaxis
• Esophagitis
• Stomatitis
• Pseudomembranous colitis

Interactions

• Strontium and tetracyclines: Severe (decreases absorption)
• Fosphenytoin and tetracyclines: Moderate (decreases concentration)
• Tetracyclines and lithium: Moderate (increases risk of lithium toxicity)
• Rifampicin and tetracyclines: Moderate (decreases exposure)
• Mitotane and tetracyclines: Unknown (decreases exposure)
• St John's Wort and tetracyclines: Unknown (decreases exposure)
• Tetracycline and antimalarials: Unknown (decreases concentration)
• Tetracycline and atovaquone: Unknown (decreases concentration)
• Tetracycline and relugolix: Unknown (increases exposure)

Precautions

• Use with caution in patients with renal impairment, as dose adjustments may be necessary
• Monitor for hepatotoxicity, pigmentation, and systemic lupus erythematosus in long-term use
• Avoid concurrent use with medications that may affect absorption or increase toxicity
• Advise patients to remain upright for at least 30 minutes after taking to prevent esophageal irritation

Pregnancy

Tetracyclines are generally not recommended during pregnancy due to the risk of dental staining and skeletal abnormalities in the developing fetus.

Breast-feeding

Tetracyclines can be excreted in breast milk and may affect the infant's dental development; caution is advised.

Storage

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

Formulations

• Tablets: 250 mg, 500 mg
• Oral suspension

Dosage

Children: Refer to specific pediatric dosing guidelines based on the identified drug, as 'hard' does not provide sufficient information.

Adults: Refer to specific drug information for dosing guidelines, as 'hard' does not specify a particular medication.

Mechanism of action

The mechanism of action for drugs termed 'hard' must be specified for accurate information, as this phrase does not designate a specific compound. Mechanisms may involve receptor interaction, enzyme inhibition, or modulation of biochemical pathways, depending on the drug in question. For example, opioid analgesics work primarily by binding to mu-opioid receptors in the central nervous system, leading to analgesic effects.

Pharmacodynamics

Pharmacodynamics refers to the effects of a drug on the body and its mechanisms of action. The pharmacodynamics of any drug classified as 'hard' would depend on its specific pharmacological profile, including its efficacy, potency, and the nature of its therapeutic effects. For instance, in the case of opioids, pharmacodynamic effects include pain relief, sedation, and potential respiratory depression.

Pharmacokinetics

Pharmacokinetics involves the absorption, distribution, metabolism, and excretion (ADME) of a drug. The pharmacokinetics of a substance termed 'hard' would vary significantly based on the specific drug. For many medications, absorption may occur via oral or parenteral routes, distribution may involve binding to plasma proteins, metabolism may occur in the liver, and excretion is typically renal. Each of these parameters is critical for understanding the drug's action and potential side effects.

Pregnancy

Consult a healthcare professional before use, as safety has not been established.

Breast-feeding

Consult a healthcare professional before use, as safety has not been established.

Storage

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

Indications

• Dry skin
• Chapped lips
• Eczema
• Skin irritation
• Nipple soreness in breastfeeding
• Cosmetic moisturization

Dosage

Children: Apply as needed to the affected area, ensuring even coverage. Refer to specific guidelines or product information for pediatric formulations.

Adults: Apply as needed to the affected area, ensuring even coverage. Frequency of application may depend on the severity of the condition and the formulation used.

Mechanism of action

Lanolin acts as an occlusive agent that forms a barrier on the skin surface, reducing transepidermal water loss and enhancing skin hydration. Its lipid composition mimics the natural lipids found in the skin, promoting a feeling of smoothness and softness. Additionally, lanolin can aid in the delivery of other active ingredients through the skin by enhancing their absorption.

Pharmacodynamics

The emollient properties of lanolin allow it to soften and soothe the skin. Its fatty acid and alcohol content contribute to its ability to create a protective layer that prevents dehydration and irritation, particularly in conditions where the skin is compromised or dry. Lanolin's hydrating effects can lead to improved skin barrier function and overall skin appearance.

Pharmacokinetics

Lanolin is not systemically absorbed to a significant extent when applied topically, indicating a low bioavailability. Its effects are primarily local, enhancing skin hydration and protection. The duration of action can vary depending on the formulation and application frequency, but it generally provides prolonged moisturization as long as it remains on the skin.

Adverse effects

• Skin irritation
• Allergic reactions
• Rash

Precautions

• Use with caution in individuals with a known allergy to wool or lanolin
• Perform a patch test prior to widespread use

Pregnancy

Lanolin is generally considered safe for use during pregnancy, but it is advisable to consult a healthcare provider before use.

Breast-feeding

Lanolin is often used as a nipple cream for breastfeeding mothers and is considered safe when used as directed.

Storage

Store in a cool, dry place away from direct sunlight. Ensure the container is tightly closed when not in use.

Formulations

• Cream
• Ointment
• Lotion

Indications

• Vision correction
• Phototherapy for skin conditions (e.g., psoriasis, eczema)
• Treatment of seasonal affective disorder (SAD)
• Circadian rhythm disorders
• Wound healing

Dosage

Children: Light therapy for paediatric patients should be approached with caution and always under professional guidance. Specific dosages will depend on the individual treatment protocol and condition being addressed.

Adults: Dosage of light therapy varies based on the condition being treated and should be tailored to individual needs, typically ranging from 15 minutes to 2 hours of exposure per day depending on the specific treatment protocol.

Mechanism of action

Light affects biological systems primarily through phototransduction, which involves the conversion of light into electrical signals within photoreceptor cells in the retina. This process initiates a cascade of biochemical reactions that ultimately lead to visual perception. In addition, specific wavelengths of light can interact with various biological molecules, triggering cellular responses such as the production of vitamin D through skin exposure to UVB radiation.

Pharmacodynamics

The pharmacodynamic effects of light are highly dependent on its wavelength and intensity. Short-wavelength blue light (around 480 nm) is known to influence circadian rhythms by affecting melatonin secretion. In therapeutic settings, light can modulate biological responses, such as promoting wound healing, reducing inflammation, and alleviating symptoms of seasonal affective disorder (SAD) through bright light therapy.

Pharmacokinetics

Light does not undergo traditional pharmacokinetic processes such as absorption, distribution, metabolism, or excretion. Instead, its effects are immediate and localized, depending on the intensity and duration of exposure. The penetration depth of light varies with wavelength; for example, UV light can penetrate the skin and affect deeper tissues, while visible light primarily affects the surface layers.

Pregnancy

There is limited data on the effects of light exposure during pregnancy. However, excessive exposure to bright light can be harmful to both the mother and the developing fetus.

Breast-feeding

Light exposure is generally considered safe while breastfeeding, but excessive exposure should be avoided to prevent potential harm to the infant.

Storage

Light should be properly controlled and managed in environments where it is used, ensuring that exposure levels are safe and effective.

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

• Used as an excipient in tablet formulations
• Used as a bulking agent in capsule formulations
• Used in food products as a thickener or stabilizer

Dosage

Children: Refer to specific product guidelines as dosage will depend on the formulation and the active ingredients.

Adults: Refer to specific product guidelines as dosage will depend on the formulation and the active ingredients.

Mechanism of action

Microcrystalline cellulose acts as a non-digestible filler that enhances the flow properties of powders during the manufacturing of tablets and capsules. It does not have a direct pharmacological action on the body but ensures that the active ingredients are effectively delivered to the patient.

Pharmacodynamics

As a non-active ingredient, microcrystalline cellulose does not exert pharmacodynamic effects typical of active pharmaceutical ingredients. Its primary role is to provide a stable and consistent matrix for the drug, facilitating the release of the active compound once ingested.

Pharmacokinetics

Microcrystalline cellulose is not absorbed in the gastrointestinal tract; it passes through the digestive system largely unchanged. It adds bulk to the stool, which may aid in promoting regular bowel movements. The substance is excreted in feces, where it contributes to dietary fiber intake.

Pregnancy

Data regarding the use of microcrystalline cellulose during pregnancy is limited. It is advisable to consult with healthcare professionals before use.

Breast-feeding

Microcrystalline cellulose is considered safe during breastfeeding, as it is not absorbed systemically.

Storage

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

Indications

• Constipation
• Dry skin
• Skin irritation

Dosage

Children: Refer to specific guidelines and prescribing information for paediatric dosing.

Adults: Refer to specific guidelines and prescribing information for adult dosing.

Mechanism of action

Paraffin acts as a lubricating agent in the gastrointestinal tract. It coats the stool and the intestinal walls, which helps to ease the passage of feces by reducing friction. This action promotes bowel movements and alleviates constipation. When used topically, it forms a barrier on the skin, which helps to retain moisture and protect against irritants.

Pharmacodynamics

Paraffin has a low viscosity and surface tension, which allows it to spread easily over surfaces. Its lubricating properties facilitate the movement of stool through the intestines, while its emollient properties help in maintaining skin hydration and barrier function. The onset of action for oral administration typically occurs within 6 to 8 hours, making it effective in treating occasional constipation.

Pharmacokinetics

Paraffin is not absorbed systemically when ingested; it remains in the gastrointestinal tract and is excreted unchanged in the feces. After oral administration, it acts locally in the intestines without significant systemic effects. When used topically, it remains on the skin surface and does not penetrate deeply, providing a protective layer without altering systemic pharmacokinetics.

Adverse effects

• Abdominal cramps
• Diarrhea
• Nausea
• Vomiting
• Lipid pneumonia (when aspirated)
• Electrolyte imbalances

Precautions

• Use with caution in patients with gastrointestinal obstruction
• Avoid in patients with a history of aspiration
• Monitor for signs of dehydration with prolonged use

Pregnancy

Use only if clearly needed. Consult a healthcare provider for advice.

Breast-feeding

Paraffin can be excreted in breast milk, use with caution.

Storage

Store at room temperature away from moisture and heat.

Formulations

• Liquid paraffin
• Soft paraffin (for topical use)

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.