CIPI-M, chlorpheniramine

CIPI-M (Chlorpheniramine maleate)

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CIPI-M (Chlorpheniramine maleate)

Chlorphenamine is an alkylamine antihistamine with H1-receptor antagonist action. It acts by reversible, competitive inhibition of the interaction of histamine with H1-receptors.

Histamine is released from mast cells on their encounter with antigens. It then binds to H1-receptors to initiate the typical symptoms of hypersensitivity and allergic responses. It acts on bronchial smooth muscles and blood vessels to produce bronchospasm and flare, wheal and itch responses to antigens. Chlorphenamine inhibits the constrictor action of histamine on smooth muscles, especially respiratory muscle and blocks the action of histamine that results in capillary permeability and formation of oedema and wheal. It also binds to H1-receptors in the Central Nervous System.

Pharmacokinetics

Chlorphenamine maleate is absorbed relatively slowly from the gastrointestinal tract, peak concentrations occurring about 2.5 to 6 hours after administration by mouth. It appears to undergo considerable first pass metabolism and about 70% of Chlorphenamine in the circulation is bound to plasma proteins. Chlorphenamine is widely distributed in the body and also crosses into the Central Nervous System.

There is a wide interindividual variation in its pharmacokinetic parameters. Chlorphenamine is extensively metabolised to desmethyl and didesmethyl chlorphenamine.

Unchanged drug and metabolites are excreted primarily in the urine with trace amounts appearing in the faeces.

Indications

Chlorphenamine is used for the symptomatic relief of allergic reactions including urticaria and angioedema, rhinitis and conjunctivitis and in pruritic skin conditions.

Dosage and administration

Adults and children over 12 years: 4mg (one tablet) every 4 to 6 hours up to a maximum of 24 mg daily

Children up to 1 year: 1mg (2.5ml) twice daily

1-6 years: 1-2mg (2.5ml-5ml) three times daily

6-12 years: 2-4mg (5ml-10ml) three or four times daily

Side effects

The side effects vary in incidence and severity with each patient.

Central Nervous System depression effects include sedation, drowsiness, deep sleep, lassitude, dizziness and inco-cordination.

Paradoxical central nervous system stimulation particularly in children may occur with insomnia, nervousness, euphoria, irritably, tremors and rarely nightmares, hallucinations and convulsions.

Antimuscarinic effects include dry mouth, thickened respiratory secretions and tightness of chest, blurred vision, urinary difficulty and retention, constipation.

Other gastrointestinal effects include nausea, vomiting, diarrhoea and epigastric pain.

Contraindications

Premature infants and neonates

Hypersensitivity to antihistamines

Precautions and warnings

Caution is required when administering to elderly patients.

Caution is required in closed-angle glaucoma, urinary retention, prostatic hypertrophy, pyloroduodenal obstruction, epilepsy, severe cardiovascular disorders, liver disorders.

Chlorphenamine may cause drowsiness. Patients should be warned not to drive or operate machinery if affected

Antihistamines may suppress positive skin test results and should be stopped several days before test.

Drug interactions

Antihistamines enhance the sedative effects of alcohol, barbiturates, hypnotics, opioid analgesics, anxiolytic sedatives, neuroleptics and should not be taken simultaneously.

Monoamine Oxidase inhibitors, atropine and tricyclic antidepressants enhance the antimuscarinic effects of antihistamines.

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