TRIMETHOBENZAMIDE HYDROCHLORIDE PRESERVATIVE FREE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for TRIMETHOBENZAMIDE HYDROCHLORIDE PRESERVATIVE FREE (TRIMETHOBENZAMIDE HYDROCHLORIDE PRESERVATIVE FREE).
Trimethobenzamide is a centrally acting antiemetic that inhibits the chemoreceptor trigger zone (CTZ) in the medulla oblongata by suppressing emetic stimuli. Its exact mechanism is not fully understood but may involve antagonism of dopamine D2 receptors and possibly serotonin 5-HT3 receptors.
| Metabolism | Hepatic metabolism via conjugation and oxidative pathways; to multiple metabolites, primarily through glucuronidation and N-demethylation. The specific CYP enzymes involved are not well characterized. |
| Excretion | Primarily renal (50-70% as unchanged drug and metabolites) and biliary (~20-30%); less than 5% fecal. |
| Half-life | Terminal elimination half-life approximately 7-9 hours in adults; prolonged in renal impairment (up to 20-30 hours). |
| Protein binding | Approximately 90% bound to plasma proteins, primarily albumin. |
| Volume of Distribution | Approximately 1.2 L/kg, indicating extensive extravascular distribution. |
| Bioavailability | Oral: 80-90% (subject to first-pass metabolism); Intramuscular: ~100%. |
| Onset of Action | Intramuscular: 15-30 minutes; Oral: 30-60 minutes; Intravenous: within minutes. |
| Duration of Action | Intramuscular: 3-4 hours; Oral: 3-4 hours; Intravenous: 2-3 hours based on antiemetic effect. |
300 mg orally or intramuscularly 3 to 4 times daily as needed for nausea and vomiting.
| Dosage form | INJECTABLE |
| Renal impairment | No specific dose adjustment guidelines are available; use with caution in severe renal impairment (CrCl <30 mL/min). |
| Liver impairment | No specific dose adjustment guidelines; use with caution in severe hepatic impairment (Child-Pugh class C). |
| Pediatric use | Not recommended for use in pediatric patients; safety and efficacy not established. |
| Geriatric use | Start at lower end of dosing range (150-200 mg every 6-8 hours) due to increased sensitivity to anticholinergic effects; monitor for dizziness and hypotension. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for TRIMETHOBENZAMIDE HYDROCHLORIDE PRESERVATIVE FREE (TRIMETHOBENZAMIDE HYDROCHLORIDE PRESERVATIVE FREE).
| Breastfeeding | Excreted in human milk in small amounts; M/P ratio not established. American Academy of Pediatrics considers compatible with breastfeeding. Monitor infant for drowsiness or anticholinergic effects. Caution in preterm or neonates due to immature hepatic function. |
| Teratogenic Risk | FDA Pregnancy Category B. Animal studies have not demonstrated fetal risk, but no adequate human studies in pregnant women. First trimester: insufficient data; use only if clearly needed. Second and third trimesters: no known specific risks, but should be used cautiously due to potential anticholinergic effects. Near term: avoid due to potential respiratory depression in neonates. |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to trimethobenzamide or any component of the formulation. Pediatric patients (especially neonates) due to benzyl alcohol content in some formulations; however, this formulation is preservative-free. Caution in patients with acute febrile illness, encephalitis, or gastroenteritis in children due to possible Reye-like syndrome.
| Precautions | May cause drowsiness, dizziness, or extrapyramidal reactions. Use with caution in patients with severe hepatic or renal impairment. Avoid use in patients with suspected viral illness due to risk of Reye's syndrome (controversial). May obscure diagnosis of appendicitis or other surgical conditions. Do not use in patients with history of seizure disorders unless benefits outweigh risks. |
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| Fetal Monitoring | Monitor maternal blood pressure, heart rate, and signs of extrapyramidal symptoms. Fetal monitoring: standard prenatal care; no specific fetal monitoring required unless maternal toxicity occurs. |
| Fertility Effects | No known significant effects on human fertility. Animal studies showed no impairment of fertility at clinically relevant doses. |