← Search & browse all drugs
DERMATOLOGICALS › ANTIPRURITICS, INCL. ANTIHISTAMINES, ANESTHETICS, ETC. › ANTIPRURITICS, INCL. ANTIHISTAMINES, ANESTHETICS, ETC. › Antihistamines for topical use
diphenhydramine
D04AA32
Forms & Strengths
- Oral capsule: 25 mg, 50 mg
- Oral tablet: 25 mg, 50 mg
- Oral liquid/elixir: 12.5 mg/5 mL
- Injectable solution: 50 mg/mL
- Topical cream/spray: 1%, 2%
Adult Dosing
- Allergic conditions / Anaphylaxis adjunctive: 25 to 50 mg PO/IV/IM every 4 to 6 hours PRN; max 300 mg/day
- Insomnia: 50 mg PO at bedtime PRN
- Motion sickness: 25 to 50 mg PO every 4 to 6 hours PRN
- Parkinsonism / Extrapyramidal symptoms: 10 to 50 mg IV/IM/PO up to 100 mg if needed; max 400 mg/day
Pediatric Dosing
- Children > 12 years: 25 to 50 mg PO/IV/IM every 4 to 6 hours PRN
- Children 6 to 12 years: 12.5 to 25 mg PO every 4 to 6 hours PRN; max 150 mg/day
- Children < 6 years: Use only under direct medical supervision for specific indications
- Allergic conditions (off-label systemic): 1.25 mg/kg or 37.5 mg/m2 PO/IV/IM divided every 6 hours; max 300 mg/day
Indications
- Symptomatic relief of allergic symptoms (rhinitis, urticaria, angioedema)
- Adjunctive treatment of anaphylactic reactions
- Treatment of motion sickness
- Short-term management of insomnia
- Control of extrapyramidal symptoms induced by neuroleptics
Mechanism of Action
- Inverse agonist at central and peripheral histamine H1 receptors
- Possesses significant anticholinergic (antimuscarinic) properties responsible for sedation and drying effects
- Local anesthetic properties via blockade of sodium channels
Contraindications
- Hypersensitivity to diphenhydramine or related antihistamines
- Neonates and premature infants
- Use during acute asthma attacks (due to thickening of respiratory secretions)
- Concurrent use with monoamine oxidase inhibitors (MAOIs)
Adverse Reactions
- Central nervous system depression (drowsiness, sedation, dizziness, impaired coordination)
- Anticholinergic effects (dry mouth, blurred vision, urinary retention, constipation)
- Paradoxical central nervous system excitation (especially in children: hyperactivity, tremors)
- Cardiovascular effects (tachycardia, hypotension, palpitations)
Drug Interactions
- Central nervous system depressants (alcohol, opioids, benzodiazepines, sedatives) result in additive sedation and respiratory depression
- Drugs with anticholinergic properties (tricyclic antidepressants, antipsychotics) increase risk of severe anticholinergic toxicity
- MAOIs prolong and intensify the anticholinergic effects of antihistamines
- May mask ototoxicity caused by aminoglycoside antibiotics
Curated Content: Needs Vetting Before Put to Clinical Use