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Phenergan (Promethazine Hydrochloride) - Description and Clinical Pharmacology

 
 



DESCRIPTION

Each rectal suppository contains 12.5 mg or 25 mg promethazine HCl with ascorbyl palmitate, colloidal silicon dioxide, white wax, hard fat, and glyceryl monostearate. Phenergan (Promethazine HCl) Suppositories, USP are for rectal administration only.

Promethazine HCl is a racemic compound; the empirical formula is C17H20N2S•HCl and its molecular weight is 320.88.

Promethazine HCl, a phenothiazine derivative, is designated chemically as 10H-Phenothiazine, 10-ethanamine, N,N α-trimethyl-, monohydrochloride, (±)- with the following structural formula:


Promethazine HCl occurs as a white to faint yellow, practically odorless, crystalline powder, which slowly oxidizes and turns blue on prolonged exposure to air. It is soluble in water and freely soluble in alcohol.

CLINICAL PHARMACOLOGY

Promethazine is a phenothiazine derivative, which differs structurally from the antipsychotic phenothiazines by the presence of a branched side chain and no ring substitution. It is thought that this configuration is responsible for its relative lack (1/10 that of chlorpromazine) of dopamine antagonist properties.

Promethazine is an H1 receptor blocking agent. In addition to its antihistaminic action, it provides clinically useful sedative and antiemetic effects.

Promethazine is metabolized by the liver to a variety of compounds; the sulfoxides of promethazine and N-demethylpromethazine are the predominant metabolites appearing in the urine.

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