What is the maximum recommended dose of hydroxyzine (antihistamine) for adults?

Maximum Recommended Dose of Hydroxyzine for Adults

The maximum recommended dose of hydroxyzine for adults is 400 mg per day, typically administered as 100 mg four times daily. 1

Dosing Guidelines by Indication

For Anxiety and Tension

• Adults: 50 to 100 mg four times daily (maximum 400 mg/day) 1
• Dosage should be adjusted according to patient response to therapy

For Pruritus Management (Allergic Conditions)

• Adults: 25 mg three or four times daily (75-100 mg/day) 1
• Effective for chronic urticaria, atopic and contact dermatoses, and histamine-mediated pruritus

For Sedation (Premedication)

• Adults: 50 to 100 mg as a single dose 1
• Can be administered before procedures or following general anesthesia

Pharmacokinetic Considerations

• Hydroxyzine has a relatively long elimination half-life of approximately 20 hours 2
• Peak plasma concentrations typically occur 2-3 hours after oral administration 3
• The drug has a large volume of distribution (16.0 L/kg) and moderate clearance rate (9.78 ml/min/kg) 2
• The long half-life suggests that once-daily dosing may be possible for some patients, though divided doses are typically recommended 3

Special Populations and Precautions

Elderly Patients

• Use with caution due to increased risk of:
  • Cognitive decline
  • Falls
  • Anticholinergic effects 4
• Consider lower doses in this population

Patients with Hepatic or Renal Impairment

• Hydroxyzine is contraindicated or should be used with caution in patients with liver or kidney disease 4
• In patients with alcohol-related liver disease, elimination half-life may be prolonged 3

Pregnancy

• Contraindicated during early pregnancy 4

Monitoring and Side Effects

• Common side effects include:

  • Sleepiness (28% vs 14% with placebo) - typically transient and most prominent during first week 5
  • Dry mouth (14% vs 5% with placebo) 5
  • Weight gain (12% vs 10% with placebo) 5
  • Loss of concentration (9% vs 8% with placebo) 5

• QT prolongation risk:

  • Hydroxyzine is listed as a QT-prolonging medication 4
  • Monitor ECG in patients with cardiac risk factors or when using other QT-prolonging medications

Timing of Administration

• Evening dosing may help mitigate daytime sedation and psychomotor impairment 6
• When used for anxiety, a single bedtime dose may maintain therapeutic effects while reducing daytime side effects 6

Clinical Pearls

• Hydroxyzine demonstrates significant suppression of histamine skin test reactivity (80% suppression of wheals and 92% suppression of flares) 2
• Antihistaminic effects can persist for 36-60 hours after a single dose 2
• Tolerance may develop with chronic use, reducing both the therapeutic and side effects 7
• For allergy testing, hydroxyzine should be discontinued 7-10 days before the procedure 4