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RESPIRATORY SYSTEM › ANTIHISTAMINES FOR SYSTEMIC USE › ANTIHISTAMINES FOR SYSTEMIC USE › Aminoalkyl ethers
doxylamine
R06AA09
Forms & Strengths
- Oral tablet 12.5 mg
- Oral tablet 25 mg
- Oral solution 6.25 mg/5 mL
- Combination tablet with pyridoxine (Diclegis) 10 mg/10 mg
Adult Dosing
- Insomnia: 12.5‑25 mg PO at bedtime, short‑term use only
- Allergic rhinitis/common cold: 12.5 mg PO every 6 h PRN, max 3‑4 doses/24 h
Pediatric Dosing
- <12 y: not recommended for insomnia
- Allergic rhinitis: 6.25 mg PO every 6‑8 h PRN, max 3 doses/24 h
- Neonates and infants <6 mo: contraindicated
Indications
- Short‑term relief of insomnia (adults)
- Symptomatic treatment of allergic rhinitis, hay fever, common cold
- Adjunct for nausea/vomiting associated with motion sickness
Mechanism of Action
- First‑generation H1‑receptor antagonist; crosses blood‑brain barrier producing sedation
- Anticholinergic activity contributes to drying of secretions and anti‑emetic effect
Contraindications
- Known hypersensitivity to doxylamine or other ethanolamine antihistamines
- Neonates/infants (risk of respiratory depression)
- Severe hepatic impairment (impaired metabolism)
- Concurrent use with MAO‑inhibitors for >14 days (risk of exaggerated CNS effects)
Adverse Reactions
- Sedation, somnolence, fatigue
- Dry mouth, blurred vision, constipation
- Urinary retention, tachycardia, palpitations
- Paradoxical excitation (especially in children)
- Anticholinergic effects: blurred vision, dilated pupils
Drug Interactions
- Additive CNS depression with alcohol, opioids, benzodiazepines, barbiturates, antihistamines
- Increased anticholinergic burden with other anticholinergics (e.g., tricyclic antidepressants)
- Potential CYP2D6 inhibition—may increase levels of CYP2D6 substrates
- Caution with QT‑prolonging agents (e.g., macrolides, fluoroquinolones) due to rare arrhythmogenic risk
Curated Content: Needs Vetting Before Put to Clinical Use