Promethazine (Promethazine Hydrochloride) - Description and Clinical Pharmacology

DESCRIPTION

Promethazine HCl Injection, USP is a sterile, pyrogen-free solution for deep intramuscular or intravenous administration. Promethazine HCl (10 H -Phenothiazine-10-ethanamine, N,N, α-trimethyl-, monohydrochloride, (±)-) is a racemic compound and has the following structural formula:

C₁₇H₂₁ClN₂S MW 320.88

Each mL contains promethazine HCl, either 25 mg or 50 mg, edetate disodium 0.1 mg, calcium chloride 0.04 mg, sodium metabisulfite 0.25 mg and phenol 5 mg in Water for Injection. pH 4.0 to 5.5; buffered with acetic acid-sodium acetate.

Promethazine HCl Injection is a clear, colorless solution. The product is light sensitive. It should be inspected before use and discarded if either color or particulate is observed.

CLINICAL PHARMACOLOGY

Promethazine HCl is a phenothiazine derivative which possesses antihistaminic, sedative, antimotion-sickness, antiemetic, and anticholinergic effects. Promethazine is a competitive H₁ receptor antagonist, but does not block the release of histamine. Structural differences from the neuroleptic phenothiazines result in its relative lack (1 / 10 that of chlorpromazine) of dopamine antagonist properties. Clinical effects are generally apparent within 5 minutes of an intravenous injection and within 20 minutes of an intramuscular injection. Duration of action is four to six hours, although effects may persist up to 12 hours. Promethazine HCl is metabolized in the liver, with the sulfoxides of promethazine and N-desmethylpromethazine being the predominant metabolites appearing in the urine. Following intravenous administration in healthy volunteers, the plasma half-life for promethazine has been reported to range from 9 to 16 hours. The mean plasma half-life for promethazine after intramuscular administration in healthy volunteers has been reported to be 9.8 ± 3.4 hours.