Phenergan (Promethazine Hydrochloride) - Description and Clinical Pharmacology

Rx only

DESCRIPTION

Each tablet of Phenergan contains 12.5 mg, 25 mg, or 50 mg promethazine HCl. The inactive ingredients present are lactose, magnesium stearate, and methylcellulose. Each dosage strength also contains the following:

12.5 mg–FD&C Yellow 6 and saccharin sodium;
25 mg–saccharin sodium;
50 mg–FD&C Red 40.

Each rectal suppository of Phenergan contains 12.5 mg, 25 mg, or 50 mg promethazine HCl with ascorbyl palmitate, silicon dioxide, white wax, and cocoa butter. Phenergan Suppositories 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 10 H -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 freely soluble in water and 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 well absorbed from the gastrointestinal tract. Clinical effects are apparent within 20 minutes after oral administration and generally last four to six hours, although they may persist as long as 12 hours. 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.