AMBODRYL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for AMBODRYL (AMBODRYL).
Antihistamine (H1-receptor antagonist) with anticholinergic and sedative properties.
| Metabolism | Hepatic via CYP450 enzymes (CYP2D6 and CYP3A4); major metabolite is diphenhydramine N-oxide. |
| Excretion | Primarily renal (70-80% as metabolites, 20-30% unchanged); biliary/fecal excretion accounts for 15-20%. |
| Half-life | Terminal elimination half-life 12-15 hours in adults; prolonged to 20-30 hours in hepatic impairment. |
| Protein binding | 98-99% bound primarily to albumin. |
| Volume of Distribution | Vd 4-6 L/kg; indicates extensive tissue distribution. |
| Bioavailability | Oral: 40-50% due to first-pass metabolism; IM: 80-90%; IV: 100%. |
| Onset of Action | Oral: 30-60 minutes; Intramuscular: 15-30 minutes; Intravenous: 1-5 minutes. |
| Duration of Action | Oral/IM: 4-6 hours (dose-dependent); IV: 2-4 hours. Clinical effect may persist longer in elderly. |
10-20 mg intramuscularly or intravenously every 4-6 hours as needed, up to a maximum of 80 mg/day.
| Dosage form | CAPSULE |
| Renal impairment | For GFR 10-50 mL/min: administer 10 mg every 6-12 hours; for GFR <10 mL/min: 10 mg every 12-18 hours. |
| Liver impairment | Child-Pugh Class A: no adjustment; Class B: reduce dose by 50%; Class C: avoid use or use with extreme caution. |
| Pediatric use | 0.1-0.2 mg/kg intramuscularly or intravenously every 4-6 hours as needed, not to exceed 10 mg per dose or 40 mg/day. |
| Geriatric use | Start at 5 mg intramuscularly or intravenously every 6-8 hours; titrate cautiously due to increased risk of anticholinergic effects and falls. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for AMBODRYL (AMBODRYL).
| Breastfeeding | Ambodryl is excreted into breast milk in low concentrations. The M/P ratio is approximately 0.5. Based on limited data, infant serum levels are usually undetectable. However, because of potential for paradoxical CNS stimulation or drowsiness in neonates, caution is advised. The American Academy of Pediatrics considers bromodiphenhydramine compatible with breastfeeding, but alternatives with better safety profiles (e.g., loratadine) are preferred. |
| Teratogenic Risk | Ambodryl (bromodiphenhydramine) is an antihistamine. In animal studies, no teratogenic effects were observed at doses up to 5 times the human dose. In humans, data are limited; first trimester use is associated with a possible small increased risk of oral clefts (odds ratio ~1.5). Second and third trimester use may cause uterine irritability and neonatal withdrawal symptoms (tremors, irritability) if used near term. Overall, risk is low but not zero. |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypersensitivity to diphenhydramine","Neonates and premature infants","Lactation (relative)"]
| Precautions | ["May cause drowsiness and impair cognitive/motor performance","Avoid alcohol and other CNS depressants","Caution in patients with asthma, increased intraocular pressure, hyperthyroidism, cardiovascular disease, hypertension"] |
| Food/Dietary | No significant food interactions. However, taking with food may reduce gastrointestinal side effects. Avoid grapefruit juice as it may theoretically increase diphenhydramine levels via CYP3A4 inhibition, though clinical significance is minimal. |
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| Fetal Monitoring | Maternal monitoring: Blood pressure, heart rate, signs of anticholinergic effects (dry mouth, urinary retention, blurred vision). Fetal monitoring: Nonstress test and biophysical profile if used in third trimester for prolonged periods due to potential for uterine irritability. Neonatal monitoring: Observe for withdrawal symptoms (irritability, tremors, respiratory depression) if used near term. |
| Fertility Effects | In animal studies, no adverse effects on fertility were observed. In humans, no specific data on fertility impact exist. Antihistamines are not known to impair fertility, though high doses may theoretically affect libido via anticholinergic effects. |
| Clinical Pearls |
| AMBODRYL (diphenhydramine) is a first-generation antihistamine with strong anticholinergic properties. It is commonly used for allergic reactions, motion sickness, and as a sleep aid. Due to its sedative effects, avoid use in elderly patients due to increased risk of falls and cognitive impairment. Use with caution in patients with glaucoma, prostate hypertrophy, or urinary retention. May cause paradoxical excitation in children. Onset of action is rapid (15-30 minutes) with duration of 4-6 hours. |
| Patient Advice | Do not drive or operate heavy machinery until you know how this medication affects you, as it causes drowsiness. · Avoid alcohol and other CNS depressants (e.g., benzodiazepines, opioids) as they increase sedation. · Do not exceed recommended dose; overdose can cause hallucinations, seizures, or cardiac arrhythmias. · If using for sleep, limit use to 7-10 days to avoid tolerance and dependence. · Report any difficulty urinating, blurred vision, or confusion, especially if elderly. |