indication

Used to prevent and relieve allergic conditions which cause pruritus (itching) and urticaria (some allergic skin reactions).

pharmacology

Trimeprazine (also known as Alimemazine) is a tricyclic antihistamine, similar in structure to the phenothiazine antipsychotics, but differing in the ring-substitution and chain characteristics. Trimeprazine is in the same class of drugs as chlorpromazine (Thorazine) and trifluoperazine (Stelazine); however, unlike the other drugs in this class, trimeprazine is not used clinically as an anti-psychotic. It acts as an anti-histamine, a sedative, and an anti-emetic (anti-nausea). Trimeprazine is used principally as an anti-emetic, to prevent motion sickness or as an anti-histamine in combination with other medications in cough and cold preparations. Tricyclic antihistamines are also structurally-related to the tricyclic antidepressants, explaining the antihistaminergic adverse effects of these two drug classes and also the poor tolerability profile of tricyclic H₁-antihistamines.

mechanism of action

Trimeprazine competes with free histamine for binding at HA-receptor sites. This antagonizes the effects of histamine on HA-receptors, leading to a reduction of the negative symptoms brought on by histamine HA-receptor binding.

toxicity

Symptoms of overdose clumsiness or unsteadiness, seizures, severe drowsiness, flushing or redness of face, hallucinations, muscle spasms (especially of neck and back), restlessness, shortness of breath, shuffling walk, tic-like (jerky) movements of head and face, trembling and shaking of hands, and insomnia.

biotransformation

Hepatic

absorption

Well absorbed in the digestive tract.

drug interactions

Bromocriptine: The phenothiazine decreases the effect of bromocriptine

Cisapride: Increased risk of cardiotoxicity and arrhythmias

Dexfenfluramine: Decreased anorexic effect, may increase psychotic symptoms

Diethylpropion: Decreased anorexic effect, may increase psychotic symptoms

Donepezil: Possible antagonism of action

Fenfluramine: Decreased anorexic effect, may increase psychotic symptoms

Galantamine: Possible antagonism of action

Guanethidine: Trimeprazine may decrease the effect of guanethidine.

Mazindol: Decreased anorexic effect, may increase psychotic symptoms

Phentermine: Decreased anorexic effect, may increase psychotic symptoms

Phenylpropanolamine: Decreased anorexic effect, may increase psychotic symptoms

Pramlintide: The anticholinergic effects of Trimeprazine may be enhanced by Pramlintide. Additive effects of reduced GI motility may occur. Pramlintide slows gastic emptying and should not be used with drugs that alter GI motility (e.g. anticholinergics). Consider alternative treatments or use caution during concomitant therapy.

Tacrine: The therapeutic effects of the central acetylcholinesterase inhibitor, Tacrine, and/or the anticholinergic, Trimeprazine, may be reduced due to antagonism. The interaction may be beneficial when the anticholinergic action is a side effect. Monitor for decreased efficacy of both agents.

Terfenadine: Increased risk of cardiotoxicity and arrhythmias

Trimethobenzamide: Trimethobenzamide and Trimeprazine, two anticholinergics, may cause additive anticholinergic effects and enhance their adverse/toxic effects. Monitor for enhanced anticholinergic effects.

Triprolidine: Triprolidine and Trimeprazine, two anticholinergics, may cause additive anticholinergic effects and enhance their adverse/toxic effects. Additive CNS depressant effects may also occur. Monitor for enhanced anticholinergic and CNS depressant effects.

Trospium: Trospium and Trimeprazine, two anticholinergics, may cause additive anticholinergic effects and enhanced adverse/toxic effects. Monitor for enhanced anticholinergic effects.