We need you! Join our contributor community and become a WikEM editor through our open and transparent promotion process.
Diphenhydramine
From WikEM
Contents
General
- Type: Antihistamines / H1 blocker
- Dosage Forms: Oral, IM, IV
- Common Trade Names: Benadryl
Adult Dosing
- Allergic reaction
- Oral: 25-50mg q4-8h, max 300mg/day
- IM/IV: 10-50mg/dose
- Parkinsonian symptoms
- Oral: 25-50mg tid-qid
- IM/IV: 10-50mg/dose
- Insomnia: 50mg PO qhs
Pediatric Dosing
- Allergic reaction
- Oral/IM/IV: 5mg/kg/day divided q6-8h (1.25-1.67mg/kg/dose)
- Alternate PO dosing
- 2-6 yo: 6.25mg q4-6h
- 6-12 yo: 12-25mg q4-6h
- >12 yo: Adult dosing
Special Populations
- Pregnancy Rating: B
- Lactation Risk: Enters breast milk
- Renal Dosing: n/a
- Hepatic Dosing: n/a
Contraindications
- Allergy to class/drug
Adverse Reactions
Serious
- Anticholinergic toxicity
- CNS depression
- Cardiac arrthymias (Sodium channel blockade)
Common
- Sedation
- Opsoclonus - conjugate irregular and nonrhythmical jerking movements of the eyes was reported in a 20-year-old woman who had ingested 5 grams[1]
Pharmacology
- Half-life: Children 5 hours, Adults 9 hours, Elderly 13.5 hours
- Metabolism: Hepatic
- Excretion: Urine
- Mechanism of Action: Antihistamines / H1 blocker
