Hydroxyzine Overview
Hydroxyzine is a first-generation antihistamine that should generally be avoided as first-line therapy for allergic rhinitis due to significant sedation, performance impairment, and anticholinergic effects, with second-generation antihistamines strongly preferred 1.
Indications
Hydroxyzine has demonstrated efficacy for:
- Allergic rhinitis (though not preferred first-line) 1
- Generalized anxiety disorder - produces statistically significant anxiolytic effects starting within the first week at 50 mg/day 2, 3
- Pruritus in atopic dermatitis - particularly effective in children 4
- Short-term insomnia treatment - when previous therapies have failed, are not tolerated, or contraindicated 5
- Chronic spontaneous urticaria (though evidence suggests no added benefit over higher-dose second-generation antihistamines alone) 6
Dosing Guidelines
Adults:
Pediatric (atopic dermatitis):
- 0.7 mg/kg three times daily is as effective as 1.4 mg/kg three times daily but causes significantly less sedation 4
- Peak serum concentration occurs at approximately 2 hours post-dose
- Elimination half-life: 7.1 hours (increases with age) 4
Contraindications (FDA Label)
Hydroxyzine is absolutely contraindicated in 7:
- Known hypersensitivity to hydroxyzine, cetirizine, or levocetirizine
- Prolonged QT interval (critical safety concern)
- Early pregnancy - causes fetal abnormalities in animal studies at doses above human therapeutic range
- Patients with previous hypersensitivity to any component
Common Side Effects
Most frequent adverse effects:
- Sedation/drowsiness (28% vs 14% placebo) - appears during first week, may progressively diminish 2
- Dry mouth (14% vs 5% placebo) 2
- Weight gain (12% vs 10% placebo) 2
- Loss of concentration (9% vs 8% placebo) 2
Critical Safety Concerns
Performance Impairment
Hydroxyzine causes significant cognitive and psychomotor impairment that persists even when dosed only at bedtime 1. Key risks include:
- Drivers taking first-generation antihistamines are 1.5 times more likely to be responsible for fatal automobile accidents 1
- Impaired driving performance worsens with cellular phone use 1
- Performance impairment can exist without subjective awareness of drowsiness 1
- Associated with impaired learning and school performance in children 1
- Increased occupational accidents and impaired work productivity 1
Morning doses cause MORE impairment than evening doses - contrary to common practice, hydroxyzine given in the morning produces larger magnitude impairment across all cognitive tasks compared to evening dosing 8.
Cardiac Risks
- QT prolongation and Torsade de Pointes can occur, especially in overdose 7
- May produce abnormal ventricular repolarization 9
- Risk increases when combined with phenothiazines, tricyclic antidepressants, antiparkinson drugs, atropine, quinidine, or procainamide 9
- ECG monitoring recommended in overdose cases 7
Anticholinergic Effects
More prominent in older adults 1:
- Dry mouth and eyes
- Constipation
- Urinary retention
- Increased risk of narrow-angle glaucoma
- Increased fall risk and fractures in elderly
- Cognitive impairment exacerbation
Drug Interactions
Avoid concomitant use with:
- Alcohol, sedatives, hypnotics, or antidepressants - significantly enhances performance impairment 1
- Other QT-prolonging agents 9
Important Clinical Pitfalls
The AM/PM dosing strategy is NOT recommended - combining a second-generation antihistamine in the morning with hydroxyzine at bedtime does NOT avoid daytime impairment because hydroxyzine and its metabolites have prolonged half-lives with end-organ effects persisting longer than plasma levels 1.
Hydroxyzine overdose differs from diphenhydramine - produces LESS antimuscarinic findings and more CNS depression compared to diphenhydramine poisoning 10. Most common manifestation is hypersedation rather than anticholinergic toxidrome 7, 10.
Adding hydroxyzine at night to second-generation antihistamines provides no additional benefit - in chronic urticaria, levocetirizine 20 mg daily alone was equally effective as levocetirizine 15 mg plus hydroxyzine 50 mg at night, but monotherapy resulted in LESS daytime somnolence 6.
Overdose Management
- Most common manifestation: hypersedation 7
- Other signs: convulsions, stupor, nausea, vomiting
- Induce vomiting if not spontaneous; perform gastric lavage
- ECG monitoring mandatory due to QT prolongation risk 7
- Hypotension: treat with IV fluids and levarterenol or metaraminol
- Do NOT use epinephrine - hydroxyzine counteracts its pressor action 7
- No specific antidote; hemodialysis not valuable unless other agents co-ingested 7