What is the recommended hydroxyzine dosing for an adult, including oral, intramuscular/intravenous routes and adjustments for hepatic impairment and elderly patients?

Hydroxyzine Dosing for Adults

For adult patients with pruritus or urticaria, prescribe hydroxyzine 10–50 mg at bedtime as an adjunct to a non-sedating antihistamine taken during the day; this regimen provides nighttime symptom control while minimizing daytime sedation and performance impairment. 1

Standard Oral Dosing

• Bedtime dosing (most common): 50 mg at bedtime is the most frequently used regimen for conditions like urticaria or pruritus, providing sustained effects into the next day due to hydroxyzine's long half-life while minimizing daytime sedation. 1

• Anxiety disorders: 50 mg/day has been studied for generalized anxiety disorder, showing efficacy with transient drowsiness as the most common side effect. 2, 3

• Multiple daily dosing: If needed for severe symptoms, 10 mg every 6 hours as needed can be used for mild symptoms, though this significantly increases the risk of daytime drowsiness, performance impairment, and cognitive effects. 1

• Avoid hydroxyzine as monotherapy: It should not be used as first-line monotherapy due to sedating properties and performance impairment; always combine with a non-sedating antihistamine during the day. 1

Intramuscular/Intravenous Dosing

No IM or IV dosing information for hydroxyzine is provided in the available evidence. The medication appears to be primarily administered via the oral route for the indications discussed. 1

Dose Adjustments for Hepatic Impairment

• Severe hepatic disease: Hydroxyzine is absolutely contraindicated and must be avoided due to the risk of excessive sedation and potential hepatic encephalopathy. 1

• Primary biliary cirrhosis: Research shows hydroxyzine elimination is significantly impaired in patients with primary biliary cirrhosis, with a mean elimination half-life of 36.6 hours (compared to normal), though specific dosing adjustments beyond avoidance in severe disease are not clearly defined. 4

Dose Adjustments for Renal Impairment

• Moderate renal dysfunction (CrCl 10-20 mL/min): Reduce the total daily hydroxyzine dose by 50%. 1

• Severe renal impairment (CrCl <10 mL/min): Hydroxyzine is absolutely contraindicated and should not be administered. 1

Elderly Patient Dosing

• Start low: Initiate therapy at the low end of the adult dosing range (10 mg at bedtime) due to age-related declines in hepatic, renal, and cardiac function. 1

• High-risk population: Older adults are at heightened risk for falls, fractures, anticholinergic effects (particularly with prostatic hypertrophy or elevated intraocular pressure), and cognitive impairment. 1

• Deprescribing consideration: Hydroxyzine is specifically listed as a medication to deprescribe in older adults due to fall risk and is among anticholinergic medications that should be avoided due to CNS impairment. 1

Practical Dosing Algorithm for Pruritus/Urticaria with Sleep Disturbance

1. Begin with a non-sedating antihistamine (e.g., loratadine 10 mg) taken in the morning. 1

2. If nighttime itching persists, add hydroxyzine 10–50 mg at bedtime. 1

3. Adjust the dose according to tolerability and renal function:

   • Halve the dose in moderate renal impairment (CrCl 10-20 mL/min). 1
   • Start at 10 mg in elderly patients. 1
   • Avoid entirely in severe renal impairment (CrCl <10 mL/min) or severe hepatic disease. 1

Critical Safety Considerations and Common Pitfalls

• Performance impairment without awareness: Hydroxyzine causes sedation and performance impairment even when patients deny subjective drowsiness; drivers taking hydroxyzine are 1.5 times more likely to be responsible for fatal automobile accidents. 1

• Avoid AM/PM split dosing: Do not use AM/PM split dosing of hydroxyzine and non-sedating antihistamines as a cost-saving strategy, as hydroxyzine's long half-life causes significant daytime impairment even with bedtime-only dosing. 1

• CNS depressant interactions: Concomitant use with other sedatives or CNS depressants dramatically enhances performance impairment and sedation. 1

• Anticholinergic cautions: Use extreme caution in patients taking other anticholinergic drugs, particularly elderly patients with prostatic hypertrophy, elevated intraocular pressure, or cognitive impairment. 1

• Occupational considerations: Hydroxyzine impairs learning, work performance, and increases occupational accidents; it should be avoided in patients requiring optimal cognitive function. 1

• Pregnancy: Hydroxyzine is the only antihistamine explicitly contraindicated during the first trimester of pregnancy. 1

• Tolerance misconception: Performance impairment can persist without subjective awareness of drowsiness, and tolerance may not develop. 1