DIMENHYDRINATE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for DIMENHYDRINATE (DIMENHYDRINATE).
Dimenhydrinate is a histamine H1 antagonist with central anticholinergic activity. It acts by blocking H1 receptors in the brain's vomiting center and inhibiting vestibular stimulation. It also has anticholinergic effects by binding to muscarinic receptors, reducing motion sickness.
| Metabolism | Primarily hepatic via CYP450 enzymes, including CYP2D6. Metabolized to diphenhydramine and 8-chlorotheophylline. |
| Excretion | Primarily renal, with 60-80% of the dose excreted unchanged in urine; minor biliary/fecal elimination accounts for <10%. |
| Half-life | Terminal elimination half-life is 5-10 hours in adults, longer in elderly or hepatic impairment (up to 15 hours). |
| Protein binding | 75-85% bound to plasma proteins, primarily albumin. |
| Volume of Distribution | Approximately 1.5 L/kg (range 1.0-2.0 L/kg), indicating extensive tissue distribution. |
| Bioavailability | Oral: 40-60% due to first-pass metabolism; IM: near 100%. |
| Onset of Action | Oral: 15-30 minutes; IM: 20-30 minutes; IV: within 1-3 minutes. |
| Duration of Action | Oral: 4-6 hours; IM/IV: 3-6 hours, with clinical effects lasting up to 8 hours in some patients. |
50-100 mg orally or intramuscularly every 4-6 hours as needed; maximum 400 mg per day. For motion sickness, 50-100 mg 30 minutes before travel.
| Dosage form | INJECTABLE |
| Renal impairment | No specific dosage adjustment is required for renal impairment. However, due to potential accumulation of active metabolites, use with caution in severe renal impairment (CrCl < 30 mL/min). |
| Liver impairment | No specific dosage adjustment is required for hepatic impairment. Use with caution in severe hepatic disease (Child-Pugh Class C) as metabolism may be impaired. |
| Pediatric use | Children 6-12 years: 25-50 mg orally or intramuscularly every 6-8 hours; maximum 150 mg per day. Children 2-6 years: 12.5-25 mg orally or intramuscularly every 6-8 hours; maximum 75 mg per day. Not recommended for children under 2 years. |
| Geriatric use | Elderly patients may be more sensitive to anticholinergic effects (e.g., confusion, urinary retention). Initiate at lower doses (e.g., 25-50 mg every 6-8 hours) and titrate carefully. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for DIMENHYDRINATE (DIMENHYDRINATE).
| Breastfeeding | Excreted into breast milk in small amounts; M/P ratio not determined. Limited data suggest no adverse effects in nursing infants. Caution due to potential anticholinergic effects on the infant. |
| Teratogenic Risk | Animal studies have shown no evidence of teratogenicity. Limited human data: no increased risk of major malformations reported with first-trimester use. Third-trimester use may cause uterine irritability and fetal distress due to anticholinergic effects. |
| Fetal Monitoring |
■ FDA Black Box Warning
None
| Serious Effects |
["Hypersensitivity to dimenhydrinate or any component","Newborns or premature infants (risk of CNS depression and anticholinergic effects)","Nursing mothers (in high doses due to potential anticholinergic effects in infant)","Acute asthma attack (due to anticholinergic effects on bronchial smooth muscle)","Porphyria (may exacerbate symptoms)"]
| Precautions | ["May cause drowsiness and impair mental alertness; caution when driving or operating machinery","Avoid alcohol and other CNS depressants","Use with caution in patients with glaucoma, prostatic hyperplasia, urinary retention, or asthma","Elderly patients may be more sensitive to anticholinergic effects","May cause paradoxical excitation in children","Pregnancy Category B: use only if clearly needed","Nursing mothers: excreted in breast milk; caution advised"] |
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| Monitor maternal heart rate and blood pressure; assess for anticholinergic effects (dry mouth, urinary retention). In late pregnancy, monitor fetal heart rate and uterine activity due to possible oxytocic and uterine relaxant effects. |
| Fertility Effects | No known adverse effects on fertility. Anticholinergic properties may theoretically affect cervical mucus or tubal motility, but no clinical evidence of impaired fertility. |