What is the appropriate dosage of hydroxyzine (Atarax) when taken as needed (prn)?

Hydroxyzine PRN Dosing for Adults

For as-needed (PRN) use in adults, hydroxyzine should be dosed at 25 mg three to four times daily for pruritus/allergic conditions, or 50-100 mg as a single dose for anxiety or sedation. 1

Standard PRN Dosing by Indication

For Pruritus and Allergic Conditions

• 25 mg three to four times daily (TID or QID) for management of pruritus due to chronic urticaria, atopic dermatitis, and contact dermatoses 1
• Alternatively, 10-50 mg at bedtime when used as a sedating antihistamine adjunct to non-sedating daytime antihistamines 2
• This bedtime dosing strategy minimizes daytime sedation while maintaining antihistamine effect 3

For Anxiety and Sedation

• 50-100 mg as a single dose for symptomatic relief of anxiety and tension 1
• 50-100 mg when used as premedication or following general anesthesia 1
• For psychoneurosis or organic disease states with anxiety manifestations, scheduled dosing of 50-100 mg QID is recommended rather than PRN 1

Critical Dosing Considerations

Renal Impairment

• Reduce dose by 50% in patients with moderate renal insufficiency (creatinine clearance 10-20 mL/min) 2

Hepatic Disease

• Avoid hydroxyzine entirely in patients with severe hepatic disease due to enhanced sedative effects 2

Elderly Patients

• Use lower dosages due to increased risk of sedative effects and anticholinergic toxicity 2

Important Clinical Pitfalls

Timing Strategy

• Evening or bedtime dosing is strongly preferred for PRN use to minimize objective psychomotor impairment and subjective drowsiness while maintaining therapeutic antihistamine effect the following day 3
• Divided daytime doses cause significantly more reaction time degradation and drowsiness compared to single evening doses 3

Duration Limitations

• Do not use as prolonged monotherapy due to concerns about reduced concentration and performance 2
• For chronic conditions requiring ongoing treatment, transition to non-sedating antihistamines for long-term management 2
• When used for mild to moderate itching, limit duration to 2-4 weeks 2

Drug Interactions to Avoid

• Do not combine with other sedative or CNS depressant medications 2
• Avoid coadministration with cholinesterase inhibitors (e.g., donepezil) as hydroxyzine's anticholinergic properties counteract therapeutic effects and worsen cognitive impairment 4
• Do not combine with benzodiazepines and SSRIs as benzodiazepines antagonize antidepressant efficacy, whereas hydroxyzine does not interfere with SSRI effectiveness 5

Contraindications

• Contraindicated in early pregnancy 2

Practical PRN Prescribing Algorithm

For allergic symptoms/pruritus:

• Start with 25 mg PRN up to QID during acute flares 1
• If nighttime symptoms predominate, use 25-50 mg at bedtime only 2
• Maximum 100 mg daily in divided doses 1

For acute anxiety or sedation needs:

• Single dose of 50-100 mg as needed 1
• Adjust based on patient response, but avoid regular scheduled use without reassessment 1