Trimethobenzamide Hydrochloride Injection, USP

The mechanism of action of Trimethobenzamide Hydrochloride Injection as determined in animals is obscure, but may involve the chemoreceptor trigger zone (CTZ), an area in the medulla oblongata through which emetic impulses are conveyed to the vomiting center; direct impulses to the vomiting center apparently are not similarly inhibited. In dogs pretreated with trimethobenzamide HCl, the emetic response to apomorphine is inhibited, while little or no protection is afforded against emesis induced by intragastric copper sulfate.

The pharmacokinetics of trimethobenzamide have been studied in healthy adult subjects. Following administration of 200 mg (100 mg/mL) Trimethobenzamide Hydrochloride IM injection, the time to reach maximum plasma concentration (T_max) was about half an hour, about 15 minutes longer for trimethobenzamide hydrochloride 300 mg oral capsule than an IM injection. A single dose of trimethobenzamide hydrochloride 300 mg oral capsule provided a plasma concentration profile of trimethobenzamide similar to Trimethobenzamide Hydrochloride Injection 200 mg IM. The relative bioavailability of the capsule formulation compared to the solution is 100%. The mean elimination half-life of trimethobenzamide is 7 to 9 hours.

Between 30 – 50% of a single dose in humans is excreted unchanged in the urine within 48 – 72 hours. The metabolic disposition of trimethobenzamide in humans is not known. Specifically, it is not known if active metabolites are generated in humans.

Trimethobenzamide hydrochloride was studied in reproduction experiments in rats and rabbits and no teratogenicity was suggested. The only effects observed were an increased percentage of embryonic resorptions or stillborn pups in rats administered 20 mg and 100 mg/kg and increased resorptions in rabbits receiving 100 mg/kg. In each study these adverse effects were attributed to one or two dams. The relevance to humans is not known. Since there is no adequate experience in pregnant or lactating women who have received this drug, safety in pregnancy or in nursing mothers has not been established.

Concomitant use of alcohol with Trimethobenzamide Hydrochloride Injection may result in an adverse drug interaction.

Clinical studies of trimethobenzamide hydrochloride did not include sufficient numbers of patients aged 65 and over to determine whether they respond differently from younger patients. Although there are studies reported in the literature that include elderly patients > 65 years old with younger patients, it is not known if there are differences in efficacy or safety parameters for elderly and non-elderly patients treated with trimethobenzamide. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

This drug is known to be substantially excreted by the kidney, and the risk of toxic reactions to this drug may be greater in patients with impaired renal function. Because elderly patients are more likely to have decreased renal function, care should be taken in dose selection, and it may be useful to monitor renal function. (See CLINICAL PHARMACOLOGY and DOSAGE AND ADMINISTRATION ).

Dose adjustment such as reducing the total dose administered at each dosing or increasing the dosing interval should be considered in elderly patients with renal impairment (creatinine clearance ≤ 70 mL/min/1.73m²). Final dose adjustment should be based upon integration of clinical efficacy and safety considerations. (See CLINICAL PHARMACOLOGY and PRECAUTIONS ).

In subjects with renal impairment (creatinine clearance ≤ 70 mL/min/1.73m²), dose adjustment such as reducing the total dose administered at each dosing or increasing the dosing interval should be considered. (See CLINICAL PHARMACOLOGY and PRECAUTIONS).

INJECTABLE, 100 mg/mL (Not for use in pediatric patients)
Usual Adult Dosage
2 mL (200 mg) t.i.d. or q.i.d. intramuscularly.

NOTE: The injectable form is intended for intramuscular administration only; it is not recommended for intravenous use.

Intramuscular administration may cause pain, stinging, burning, redness and swelling at the site of injection. Such effects may be minimized by deep injection into the upper outer quadrant of the gluteal region, and by avoiding the escape of solution along the route.

Discard unused portion.