NORFLEX-CO

Indications

• Mild to moderate pain
• Fever
• Headaches
• Muscle aches
• Arthritis
• Backaches
• Toothaches
• Colds

Dosage

Adults: For adults, the typical dosage is 500 mg to 1 g every 4 to 6 hours, with a maximum daily limit of 4 g. In cases of intravenous administration, the dosage is 15 mg/kg every

Mechanism of action

Paracetamol is thought to exert its analgesic effects by inhibiting cyclo-oxygenase (COX) enzymes, specifically COX-1 and COX-2, which are involved in the synthesis of prostaglandins responsible for pain sensation. Unlike most NSAIDs, paracetamol does not exhibit peripheral anti-inflammatory effects. Its antipyretic action is believed to result from direct action on heat-regulating centers in the brain, leading to peripheral vasodilation and sweating.

Pharmacodynamics

Paracetamol has been shown to have both antipyretic and analgesic effects, lacking any significant anti-inflammatory activity. It does not interfere with platelet aggregation or disrupt hemostasis, making it a safer option for individuals at risk of bleeding. Allergic reactions to paracetamol are rare. The drug does not affect uric acid secretion or acid-base balance when used at recommended doses.

Pharmacokinetics

Paracetamol is rapidly absorbed from the gastrointestinal tract, with peak plasma concentrations typically occurring within 30 to 60 minutes after oral administration. It is primarily metabolized in the liver via conjugation with glucuronide and sulfate, with a minor pathway involving cytochrome P450 enzymes. The elimination half-life ranges from 1 to 4 hours, with renal excretion of metabolites as the primary route of elimination.

Adverse effects

• Nausea and vomiting
• Liver injury
• Renal damage
• Hypersensitivity reactions
• Flushing
• Hypotension
• Anorectal erythema
• Angioedema
• Agranulocytosis
• Thrombocytopenia
• Leukopenia
• Severe cutaneous adverse reactions (SCARs)

Interactions

• Increased risk of methaemoglobinaemia with topical prilocaine
• Increased risk of methaemoglobinaemia with topical anaesthetics
• Increased anticoagulant effect with coumarins
• Increased risk of hepatotoxicity with imatinib
• Decreased exposure with rifampicin
• Decreased exposure with pitolisant

Precautions

• Monitor patients with liver disease or heavy alcohol use for increased risk of hepatotoxicity
• Adjust doses in patients taking enzyme-inducing antiepileptic medications
• Use caution in patients with renal impairment
• Clinical judgement is required for dose adjustment in weight-based dosing

Pregnancy

Paracetamol is generally considered safe to use during pregnancy for pain and fever relief, but should be used at the lowest effective dose for the shortest duration necessary.

Breast-feeding

Paracetamol is excreted in breast milk in small amounts and is considered safe for use while breastfeeding.

Storage

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

Formulations

• Oral tablets (500 mg)
• Oral suspension (120 mg/5 mL, 500 mg/5 mL)
• Rectal suppositories (various strengths)
• Intravenous infusion (various strengths)

Indications

• Parkinson's disease
• Nocturnal akinesia
• Drooling of saliva in Parkinson's disease

Dosage

Children: Refer to the BNF for Children for specific dosing information, as pediatric dosing is based on individual patient assessment.

Adults: Refer to the BNF for specific dosing information, as doses may vary based on the condition being treated.

Mechanism of action

Orphenadrine acts as an anticholinergic agent, antagonizing muscarinic receptors in the central nervous system. This reduces the activity of acetylcholine, thereby balancing the neurotransmitter levels disrupted by dopamine deficiency. The reduction in cholinergic activity helps alleviate symptoms of Parkinson's disease and other movement disorders.

Pharmacodynamics

The drug has a significant effect in reducing tremors and rigidity associated with Parkinson's disease. By blocking cholinergic receptors, orphenadrine helps to restore the balance between dopaminergic and cholinergic systems, thus improving motor function. Its sedative properties may also contribute to its therapeutic effects.

Pharmacokinetics

Orphenadrine is well-absorbed after oral administration, with peak plasma concentrations occurring within 1-3 hours. It has a large volume of distribution, indicating extensive tissue binding. The drug is metabolized in the liver and has a half-life of approximately 14 hours. Renal excretion plays a minor role in its elimination, as the metabolites are primarily excreted in urine.

Contra-indications

• Hypersensitivity to orphenadrine or any component of the formulation
• Glaucoma
• Prostatic hypertrophy
• Urinary retention
• Myasthenia gravis

Adverse effects

• Dry mouth
• Dizziness
• Constipation
• Blurred vision
• Sedation
• Nausea
• Confusion
• Hallucinations

Interactions

• Increased sedative effects with alcohol, antihistamines, and other CNS depressants
• Anticholinergic effects may be enhanced with other anticholinergics
• May reduce the effectiveness of certain medications for Parkinson's disease

Precautions

• Use with caution in patients with a history of cardiovascular disease
• Monitor for signs of urinary retention
• Avoid abrupt withdrawal to prevent potential withdrawal symptoms
• Caution in the elderly or those with cognitive impairment

Pregnancy

Use during pregnancy only if the potential benefit justifies the potential risk to the fetus. Limited data on safety.

Breast-feeding

Orphenadrine is excreted in breast milk; use with caution in nursing mothers.

Storage

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

Formulations

• Orphenadrine hydrochloride 100 mg tablets
• Orphenadrine hydrochloride 35 mg/5 mL oral solution

Indications

• Acute painful musculoskeletal conditions
• Parkinson's disease
• Parkinsonian syndromes

Dosage

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

Adults: Refer to the BNF for specific dosing recommendations, typically starting at 100 mg orally twice daily, adjusted based on response and tolerance.

Mechanism of action

Orphenadrine binds to and inhibits histamine H1 receptors and NMDA receptors. It counteracts the stimulation of the cholinergic system due to dopamine deficiency in the striatum, exerting an anticholinergic effect that helps relieve motor disturbances. This action reduces voluntary muscle spasms by central antimuscarinic action, selectively depressing spinal polysynaptic reflexes over monosynaptic reflexes.

Pharmacodynamics

Orphenadrine is indicated as an adjunct to rest, physical therapy, and other measures for the relief of discomfort associated with acute painful musculoskeletal conditions. It mainly acts centrally as an anticholinergic, with a weak peripheral effect. It also helps restore the balance between cholinergic and dopaminergic neurotransmission in conditions like Parkinson's disease, improving rigidity and tremor, though its effect on bradykinesia is less pronounced.

Pharmacokinetics

Orphenadrine is well absorbed after oral administration, with peak plasma concentrations typically reached within 1 to 2 hours. It has a half-life of approximately 14 hours, allowing for once or twice daily dosing. The drug is metabolized in the liver and excreted primarily in urine, with a small percentage eliminated unchanged. Its pharmacokinetic profile may be influenced by factors such as liver function and patient age.

Adverse effects

• Dizziness
• Drowsiness
• Dry mouth
• Nausea
• Confusion
• Blurred vision
• Constipation

Interactions

• clozapine+orphenadrine: Unknown (additive effect)
• antipsychotics, second generation+orphenadrine: Unknown (additive effect)

Precautions

• Use with caution in patients with glaucoma
• Use with caution in patients with urinary retention
• Use with caution in elderly patients due to increased sensitivity to anticholinergic effects

Pregnancy

Orphenadrine should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. It is categorized as a pregnancy category C drug.

Breast-feeding

Orphenadrine is excreted in breast milk. Caution should be exercised when administering to nursing mothers.

Storage

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

Formulations

• Tablets
• Syrup

Mechanism of action

Orphenadrine binds and inhibits both histamine H1 receptors and NMDA receptors. It restores the motor disturbances induced by neuroleptics, in particular the hyperkinesia. The dopamine deficiency in the striatum increases the stimulating effects of the cholinergic system. This stimulation is counteracted by the anticholinergic effect of orphenadrine. It may have a relaxing effect on skeletal muscle spasms and it has a mood elevating effect. ANTIPARKINSONISM DRUGS ALSO BLOCK CHOLINERGIC RECEPTORS. THEY ARE... ORPHENADRINE (DISIPAL)... BLOCKADE PREVENTS ACTIONS OF ACETYLCHOLINE RELEASED FROM PARASYMPATHETIC NERVE ENDINGS. ...REDUCES VOLUNTARY MUSCLE SPASM BY CENTRAL ANTIMUSCARINIC ACTION & RESEMBLES ATROPINE IN THIS RESPECT. /CITRATE/ NEURONAL CONDUCTION, NEUROMUSCULAR TRANSMISSION, & MUSCLE EXCITABILITY ARE NOT DEPRESSED EXCEPT AFTER NEARLY LETHAL DOSES. PROMINENT EFFECT...IS TO DEPRESS SPINAL POLYSYNAPTIC REFLEXES PREFERENTIALLY OVER MONOSYNAPTIC REFLEXES. /CENTRALLY ACTING MUSCLE RELAXANTS/

Pharmacodynamics

Orphenadrine is indicated as an adjunct to rest, physical therapy, and other measures for the relief of discomfort associated with acute painful musculoskeletal conditions. Orphenadrine is an anticholinergic with a predominantly central effect and only a weak peripheral effect. In addition, it has mild antihistaminic and local anaesthetic properties. Parkinson's syndrome is the consequence of a disturbed balance between cholinergic and dopaminergic neurotransmission in the basal ganglia caused by a decrease in dopamine. Orphenadrine restores the physiological equilibrium and has a favourable effect on the rigidity and tremor of Parkinson's disease and Parkinsonian syndromes. The effect is somewhat less on bradykinesia.

Mechanism of action

According to its FDA labeling, acetaminophen's exact mechanism of action has not been fully established - despite this, it is often categorized alongside NSAIDs (non-steroidal anti-inflammatory drugs) due to its ability to inhibit the cyclo-oxygenase (COX) pathways. It is thought to exert central actions which ultimately lead to the alleviation of pain symptoms. One theory is that acetaminophen increases the pain threshold by inhibiting two isoforms of cyclo-oxygenase, COX-1 and COX-2, which are involved in prostaglandin (PG) synthesis. Prostaglandins are responsible for eliciting pain sensations. Acetaminophen does not inhibit cyclooxygenase in peripheral tissues and, therefore, has no peripheral anti-inflammatory effects. Though acetylsalicylic acid (aspirin) is an irreversible inhibitor of COX and directly blocks the active site of this enzyme, studies have shown that acetaminophen (paracetamol) blocks COX indirectly. Studies also suggest that acetaminophen selectively blocks a variant type of the COX enzyme that is unique from the known variants COX-1 and COX-2. This enzyme has been referred to as _COX-3_. The antipyretic actions of acetaminophen are likely attributed to direct action on heat-regulating centers in the brain, resulting in peripheral vasodilation, sweating, and loss of body heat. The exact mechanism of action of this drug is not fully understood at this time, but future research may contribute to deeper knowledge. Although further investigation is warranted, the active metabolite of acetaminophen (AM404) was shown to interact with several molecular targets, including the Ca_v3.2 calcium channel, the cannabinoid CB1 receptors, TRPV1 receptors, and Na_v1.8 and Na_v1.7 channels. Acetaminophen produces analgesia and antipyresis by a mechanism similar to that of salicylates. Unlike salicylates, however, acetaminophen does not have uricosuric activity. There is some evidence that acetaminophen has weak anti-inflammatory activity in some nonrheumatoid conditions (e.g., in patients who have had oral surgery). ... Acetaminophen lowers body temperature in patients with fever but rarely lowers normal body temperature. The drug acts on the hypothalamus to produce antipyresis; heat dissipation is increased as a result of vasodilation and increased peripheral blood flow. The effects of acetaminophen on cyclooxygenase activity have not been fully determined. Acetaminophen is a weak, reversible, isoform-nonspecific cyclooxygenase inhibitor at dosages of 1 g daily. The inhibitory effect of acetaminophen on cyclooxygenase-1 is limited, and the drug does not inhibit platelet function. Therapeutic doses of acetaminophen appear to have little effect on cardiovascular and respiratory systems; however, toxic doses may cause circulatory failure and rapid, shallow breathing. Acetaminophen (N-acetyl-p-aminophenol (APAP)) is the most common antipyretic/analgesic medicine worldwide. If APAP is overdosed, its metabolite, N-acetyl-p-benzo-quinoneimine (NAPQI), causes liver damage. However, epidemiological evidence has associated previous use of therapeutic APAP doses with the risk of chronic obstructive pulmonary disease (COPD) and asthma. The transient receptor potential ankyrin-1 (TRPA1) channel is expressed by peptidergic primary sensory neurons. Because NAPQI, like other TRPA1 activators, is an electrophilic molecule, /the researchers/ hypothesized that APAP, via NAPQI, stimulates TRPA1, thus causing airway neurogenic inflammation. NAPQI selectively excites human recombinant and native (neuroblastoma cells) TRPA1. TRPA1 activation by NAPQI releases proinflammatory neuropeptides (substance P and calcitonin gene-related peptide) from sensory nerve terminals in rodent airways, thereby causing neurogenic edema and neutrophilia. Single or repeated administration of therapeutic (15-60 mg/kg) APAP doses to mice produces detectable levels of NAPQI in the lung, and increases neutrophil numbers, myeloperoxidase

Pharmacodynamics

Animal and clinical studies have determined that acetaminophen has both antipyretic and analgesic effects. This drug has been shown to lack anti-inflammatory effects. As opposed to the _salicylate_ drug class, acetaminophen does not disrupt tubular secretion of uric acid and does not affect acid-base balance if taken at the recommended doses. Acetaminophen does not disrupt hemostasis and does not have inhibitory activities against platelet aggregation. Allergic reactions are rare occurrences following acetaminophen use.