Is 100 mg twice daily (bid) of hydroxyzine (hydroxyzine) as needed (prn) an appropriate dose for an adult patient with anxiety?

Hydroxyzine 100 mg BID PRN for Adult Anxiety

No, 100 mg twice daily (BID) PRN is not the appropriate dosing regimen for hydroxyzine in adult anxiety—the FDA-approved dose is 50-100 mg four times daily (QID), not BID, and PRN dosing is not optimal for generalized anxiety disorder. 1

FDA-Approved Dosing for Anxiety

The FDA label clearly specifies that for symptomatic relief of anxiety and tension associated with psychoneurosis, the approved adult dose is 50-100 mg QID (four times daily), not BID. 1 This means:

• Total daily dose range: 200-400 mg divided into 4 doses throughout the day 1
• Your proposed 100 mg BID would only provide 200 mg daily in 2 doses, which underutilizes the medication's dosing schedule
• The QID schedule maintains more consistent blood levels throughout the day for anxiety control 1

Why PRN Dosing Is Problematic for GAD

Hydroxyzine should be dosed on a scheduled basis (QID), not PRN, for generalized anxiety disorder. 2, 3 Here's why:

• Clinical trials demonstrating efficacy used fixed daily dosing of 50 mg/day, showing significant anxiolytic effects beginning in the first week that were maintained throughout 4 weeks of continuous treatment 2
• The therapeutic effect requires steady-state levels—anxiety reduction was sustained with regular dosing and persisted even after abrupt discontinuation without rebound 2
• PRN dosing fails to provide the consistent drug levels needed for the cognitive component of anxiety that hydroxyzine targets 3

Correct Dosing Strategy

Start with hydroxyzine 50 mg QID (four times daily) on a scheduled basis, not PRN. 1, 2 The dosing approach should be:

• Initial dose: 50 mg four times daily (total 200 mg/day) 1
• Can increase to 100 mg QID (400 mg/day) if needed and tolerated 1
• Expect onset of anxiolytic effect within the first week 2, 3
• Most common side effect is transient sleepiness (28% of patients) that appears during the first week and progressively diminishes with continued treatment 2

Important Clinical Considerations

Hydroxyzine has limited high-quality evidence for GAD and should not be considered a first-line agent. 4 Key caveats include:

• A Cochrane review found hydroxyzine more effective than placebo but noted high risk of bias in included studies and small sample sizes 4
• Benzodiazepines remain more established for acute anxiety, with lorazepam 0.5-1 mg orally up to four times daily being a guideline-recommended option 5
• For elderly or debilitated patients, reduce benzodiazepine doses to 0.25-0.5 mg (maximum 2 mg in 24 hours) 5
• Hydroxyzine showed equivalent efficacy to benzodiazepines and buspirone in head-to-head trials, but with higher rates of sleepiness/drowsiness 4

Monitoring and Adjustment

Adjust dosage according to the patient's response to therapy, as emphasized in the FDA label. 1 Specific monitoring includes:

• Assess response after 1 week of scheduled dosing (not PRN) 2, 3
• Sleepiness typically resolves with continued treatment despite maintaining the same dose 2
• Other side effects to monitor: weight gain (12%), dry mouth (14%), loss of concentration (9%), and insomnia (9%) 2
• No organ toxicity or dependency has been demonstrated with hydroxyzine 3

The correct prescription should read: Hydroxyzine 50 mg PO QID (scheduled), not 100 mg BID PRN.