HYDRAMINE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for HYDRAMINE (HYDRAMINE).
Antagonist of histamine H1 receptors, preventing histamine-mediated responses such as vasodilation, bronchoconstriction, and increased capillary permeability.
| Metabolism | Hepatic via CYP450 enzymes (primarily CYP2D6 and CYP3A4); metabolites include diphenhydramine and norfluoxetine. |
| Excretion | Primarily renal (95%) as metabolites; <5% unchanged; 5% fecal |
| Half-life | Terminal elimination half-life 5.7 hours, range 4.2-7.7 hours; prolonged in hepatic impairment (up to 15 hours in cirrhosis) |
| Protein binding | 75-85% bound to albumin, α1-acid glycoprotein, and lipoproteins |
| Volume of Distribution | 6.5-8 L/kg (0.8-1.2 L/kg in neonates); extensive tissue distribution, crosses blood-brain barrier |
| Bioavailability | Oral: 40-60% due to extensive first-pass metabolism; sublingual: not available; intramuscular: 80-100% |
| Onset of Action | Oral: 30-45 minutes; Intravenous: within minutes (rapid distribution); Intramuscular: 15-30 minutes |
| Duration of Action | Oral: 4-6 hours; Intravenous/Intramuscular: 3-4 hours. Clinical sedation often shorter (2-4 hours) due to tolerance |
50-100 mg IV/IM every 4-6 hours, maximum 400 mg per day. Also available as 50 mg oral tablets.
| Dosage form | SYRUP |
| Renal impairment | CrCl 10-50 mL/min: administer every 6-8 hours; CrCl <10 mL/min: administer every 8-12 hours. |
| Liver impairment | Child-Pugh Class B or C: reduce dose by 50% or extend dosing interval to every 8-12 hours. |
| Pediatric use | 1.25 mg/kg IV/IM every 6 hours (maximum single dose 50 mg). Oral: 5 mg/kg/day divided every 6 hours. |
| Geriatric use | Start at 25 mg every 6-8 hours; increase cautiously due to increased risk of anticholinergic effects and confusion. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for HYDRAMINE (HYDRAMINE).
| Breastfeeding | Not recommended during breastfeeding. No data on M/P ratio; antihistamines may be excreted into breast milk and could cause irritability or drowsiness in infants. Consider alternatives. |
| Teratogenic Risk | FDA Pregnancy Category C. First trimester: No adequate studies in humans; animal studies have shown teratogenic effects at high doses. Avoid use unless benefit outweighs risk. Second and third trimesters: No specific fetal risks reported, but anticholinergic effects may cause fetal tachycardia or meconium ileus. Use with caution. |
■ FDA Black Box Warning
None.
| Serious Effects |
Hypersensitivity to hydramine or its components. Concurrent use with MAOIs. Severe liver disease. Neonates and premature infants. Nursing mothers.
| Precautions | May cause drowsiness; avoid driving or operating machinery. Use with caution in patients with asthma, glaucoma, prostatic hyperplasia, or hepatic impairment. Elderly patients more sensitive to anticholinergic effects. |
| Food/Dietary | No significant food interactions; alcohol should be avoided due to additive CNS depression. |
| Clinical Pearls |
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| Fetal Monitoring |
| Monitor for maternal anticholinergic effects (dry mouth, blurred vision, urinary retention). Fetal heart rate monitoring advised if used in third trimester due to potential for fetal tachycardia. |
| Fertility Effects | No significant effects on fertility reported in animal studies. In humans, no data available; theoretical risk due to anticholinergic effects on cervical mucus or ovulation. |
| Hydramine (diphenhydramine) is a first-generation antihistamine with strong anticholinergic effects. Use with caution in elderly due to increased risk of confusion, falls, and urinary retention. Avoid in patients with narrow-angle glaucoma, prostatic hypertrophy, or during acute asthma attacks. Sedative effects can be utilized for sleep but tolerance develops quickly; not recommended for chronic insomnia. |
| Patient Advice | Take exactly as prescribed; do not exceed recommended dose. · This medication may cause drowsiness or dizziness; avoid driving or operating machinery until you know how it affects you. · Avoid alcohol and other CNS depressants while taking this drug. · Do not use for longer than recommended for sleep; tolerance may develop. · Report any vision changes, difficulty urinating, or rapid heartbeat to your healthcare provider. · Store at room temperature away from moisture and heat. · Keep out of reach of children; overdose may be fatal. |