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. |
| Molecular Weight | 390.86 |
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 | Human data limited; animal studies show no evidence of fetal harm; use only if clearly needed. Avoid in first trimester due to theoretical risk of neural tube defects from antiemetic use. |
| 2nd trimester | Generally considered safe for short-term use; no significant teratogenicity reported. Monitor for maternal hypotension and drowsiness. |
| 3rd trimester | Use near term may cause extrapyramidal symptoms in neonate; avoid prolonged use or high doses. Use only if benefit outweighs risk. |
Clinical note
Comprehensive clinical and safety monograph for TRIMETHOBENZAMIDE HYDROCHLORIDE PRESERVATIVE FREE (TRIMETHOBENZAMIDE HYDROCHLORIDE PRESERVATIVE FREE).
| Placental transfer | Crosses placenta; degree unknown but expected based on molecular weight and lipid solubility. |
| Breastfeeding | Excreted into breast milk in small amounts; no adverse effects reported in infants. Caution with large doses or prolonged use due to potential for sedation or extrapyramidal effects. Monitor infant for drowsiness or feeding difficulties. |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to trimethobenzamide or any componentChildren < 2 years (due to risk of extrapyramidal reactions)Acute febrile illness with dehydration or encephalopathy (risk of 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. |
| Food/Dietary | No specific food interactions have been reported. However, taking with food may reduce gastrointestinal upset. Avoid excessive alcohol intake as it may increase sedation and dizziness. |
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| Lactation Rating | L2 (Safer) |
| 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. |
| 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. |
| Clinical Pearls | Trimethobenzamide is a centrally acting antiemetic with antihistaminergic properties. It is less effective than other antiemetics for severe vomiting. Use with caution in children and elderly due to risk of extrapyramidal symptoms and sedation. Can cause drowsiness and dizziness. Avoid in patients with hypersensitivity to similar drugs or with suspected intestinal obstruction. |
| Patient Advice | Take this medication exactly as prescribed, usually 3-4 times daily as needed for nausea and vomiting. · This drug may cause drowsiness or dizziness; avoid driving or operating machinery until you know how it affects you. · Do not consume alcohol or other central nervous system depressants while taking this medication. · Contact your healthcare provider if symptoms persist or worsen after 1-2 days of treatment. · This product is preservative-free; do not use if the solution appears cloudy or contains particles. · Keep out of reach of children and store at room temperature away from moisture and heat. |