Chlorphenamine

Chlorphenamine (INN) or chlorpheniramine (USAN, former BAN), commonly marketed as its salt chlorphenamine maleate (CPM; Chlor-Trimeton&reg;, Piriton&reg;, Chlor-Tripolon&reg;), is a first-generation alkylamine antihistamine used in the prevention of the symptoms of allergic conditions such as rhinitis and urticaria. Its sedative effects are relatively weak compared to other first-generation antihistamines. Chlorpheniramine is one of the most commonly used antihistamines in small-animal veterinary practice as well.

Chlorpheniramine is part of a series of antihistamines including pheniramine (Naphcon®) and its halogenated derivatives and others including fluorpheniramine, chlorpheniramine, dexchlorpheniramine (Polaramine®), brompheniramine (Dimetapp®), dexbrompheniramine (Drixoral®) deschlorpheniramine, dipheniramine (also known as triprolidine with the trade name Actifed®) iodopheniramine &c.

The halogenated alkylamine antihistamines all exhibit optic isomerism and chlorpheniramine in the indicated products is racaemic chlorpheniramine maleate whereas dexchlorpheniramine (Polaramine®) is the dextrorotary (right-handed) stereoisomer.

Chlorphenamine has antidepressant properties, inhibiting reuptake of the neurotransmitter serotonin. Based on this knowledge, the Swedish company Astra AB was able to derive the first marketed selective serotonin reuptake inhibitor, zimelidine, from chlorphenamine. Like other agents of this type, it also has analgesic-sparing (potentiating) effects on opioid analgesics, commonly reducing codeine, dihydrocodeine, and hydrocodone requirements by 10 to 35 per cent.