What is the recommended dosage of Hydroxazine (hydroxyzine) for an adult patient with anxiety or itching, considering potential interactions and underlying conditions like impaired renal or hepatic function?

Hydroxyzine Dosing for Adults

For anxiety in adults, hydroxyzine 50-100 mg four times daily is the FDA-approved dosage, while for pruritus (itching), the recommended dose is 25 mg three to four times daily, though bedtime dosing of 10-50 mg is strongly preferred to minimize daytime sedation and performance impairment. 1

Standard Dosing Regimens

For Anxiety

• FDA-approved dosing: 50-100 mg four times daily for symptomatic relief of anxiety and tension 1
• Clinical trials demonstrate efficacy at 50 mg daily for generalized anxiety disorder, with superiority over placebo from the first week of treatment 2
• Hydroxyzine shows greater and more rapid cognitive improvement compared to lorazepam in controlled trials 2

For Pruritus (Itching)

• FDA-approved dosing: 25 mg three to four times daily for allergic conditions including chronic urticaria, atopic dermatitis, and contact dermatoses 1
• Preferred regimen: 10-50 mg at bedtime as adjunctive therapy to non-sedating antihistamines during the day 3
• The 50 mg bedtime dose is the most commonly used regimen for urticaria or pruritus, minimizing daytime sedation while providing sustained symptom control due to hydroxyzine's long half-life 3

Critical Safety Considerations and Performance Impairment

Hydroxyzine causes significant sedation and performance impairment even when patients deny subjective drowsiness, and drivers taking hydroxyzine are 1.5 times more likely to be responsible for fatal automobile accidents. 3

• Performance impairment persists without subjective awareness of drowsiness, and tolerance does not develop 3
• Hydroxyzine impairs learning, work performance, and increases occupational accidents 3
• Multiple daily dosing significantly increases the risk of daytime drowsiness, performance impairment, and cognitive effects 3
• Bedtime-only dosing maintains H1-receptor antagonism the following morning while alleviating the prolongation of reaction times seen with divided doses 4

Dose Adjustments for Special Populations

Renal Impairment

• Moderate renal insufficiency (creatinine clearance 10-20 mL/min): Reduce dose by half 3, 5
• Severe renal impairment: Avoid hydroxyzine 6

Hepatic Impairment

• Severe hepatic disease: Avoid hydroxyzine entirely due to sedative effects 3, 5
• Elderly adults should be started at the low end of the dosing range due to decreased hepatic, renal, or cardiac function 3

Elderly Patients

• Lower dosages should be considered due to increased risk of sedative and anticholinergic effects 3
• Hydroxyzine is listed among anticholinergic medications that should be avoided in older adults due to CNS impairment and fall risk 3
• Hydroxyzine is specifically listed as a medication to deprescribe in older adults due to fall risk 3
• Elderly patients are at high risk for side effects, particularly with pre-existing conditions like prostatic hypertrophy, elevated intraocular pressure, or cognitive impairment 3

Pregnancy

• Contraindicated during early stages of pregnancy 3, 5
• Avoid antihistamines if possible, especially during the first trimester 5

Drug Interactions and Contraindications

• Avoid concomitant use with other CNS depressants (alcohol, benzodiazepines, opioids), as this dramatically enhances performance impairment and sedation 3
• Use caution in patients taking other anticholinergic drugs, particularly elderly patients with prostatic hypertrophy, elevated intraocular pressure, or cognitive impairment 3
• Hydroxyzine's sedating and anticholinergic properties make it inappropriate for use in delirium management 3

Optimal Dosing Strategy to Minimize Adverse Effects

The preferred approach is bedtime-only dosing (10-50 mg) as an adjunct to non-sedating antihistamines during the day, rather than multiple daily doses. 3

• Bedtime dosing provides sustained effects into the next day due to hydroxyzine's long half-life 3
• Avoid AM/PM split dosing of hydroxyzine and non-sedating antihistamines, as hydroxyzine's long half-life causes significant daytime impairment even with bedtime-only dosing 3
• Extended monotherapy with hydroxyzine is not recommended; favor its use as a nighttime adjunct to non-sedating antihistamines 3
• For mild to moderate itching, hydroxyzine can be used for 2-4 weeks, with transition to non-sedating antihistamines for long-term management 3

Common Pitfalls to Avoid

• Do not rely on patient-reported drowsiness as an indicator of performance impairment—objective impairment occurs even without subjective symptoms 3, 7
• Do not use hydroxyzine in patients requiring optimal cognitive function or operating machinery/vehicles 3
• Do not prescribe multiple daily doses when bedtime dosing can achieve therapeutic goals with less impairment 3
• Hydroxyzine causes 80% sedation rates compared to 50% with diphenhydramine and 60-73% with promethazine 3