What is a safe dosing regimen for Atarax (hydroxyzine) at night and Zyrtec (cetirizine) in the morning?

Safe Dosing Regimen for Atarax (Hydroxyzine) and Zyrtec (Cetirizine)

The safest dosing regimen is 10 mg of cetirizine (Zyrtec) in the morning and 10-25 mg of hydroxyzine (Atarax) at bedtime, with the hydroxyzine dose adjusted based on sedation needs and patient response. 1

Rationale for This Regimen

Morning Dose: Cetirizine (Zyrtec)

• Cetirizine 10 mg is the standard recommended dose for allergic conditions and provides 24-hour coverage with minimal sedation when taken in the morning 1
• As a second-generation antihistamine, cetirizine causes significantly less daytime drowsiness and performance impairment compared to first-generation antihistamines like hydroxyzine 1
• At the standard 10 mg dose, cetirizine may cause mild drowsiness in some patients (13.7% vs 6.3% with placebo) but typically without significant performance impairment 1
• Taking cetirizine in the morning minimizes any potential impact of its mild sedative properties on daytime activities 1

Evening Dose: Hydroxyzine (Atarax)

• Hydroxyzine 10-25 mg at bedtime utilizes its sedative properties to help with sleep while managing allergic symptoms overnight 1
• The sedative effect of hydroxyzine can be beneficial when taken at bedtime for patients who need help with sleep 1
• Starting at the lower dose (10 mg) is recommended, especially in older adults or those sensitive to sedative effects 1

Important Considerations

Potential Risks

• First-generation antihistamines like hydroxyzine have been associated with:
  • Next-day drowsiness and performance impairment even when dosed only at bedtime 1
  • Anticholinergic effects including dry mouth, constipation, urinary retention, and increased risk of narrow-angle glaucoma 1
  • Increased risk of falls and cognitive impairment, particularly in older adults 1

Special Populations

• Older adults: Use hydroxyzine with extra caution due to increased sensitivity to psychomotor impairment and anticholinergic effects 1
• Patients with liver disease: Consider lower doses of both medications as metabolism may be impaired 2
• Patients with renal impairment: Dose adjustment may be necessary, particularly for cetirizine which is primarily eliminated through the kidneys 3

Avoiding Common Pitfalls

• Avoid the AM/PM strategy with standard doses: Guidelines specifically caution against the strategy of using a second-generation antihistamine in the morning and a first-generation antihistamine at night at full doses, as the sedative effects of hydroxyzine can persist into the next day 1
• Monitor for cumulative anticholinergic burden: Be aware that hydroxyzine contributes to overall anticholinergic burden, which can be problematic when combined with other medications with anticholinergic properties 1
• Do not exceed recommended doses: Higher doses of cetirizine (>10 mg) may increase sedation, while higher doses of hydroxyzine significantly increase risk of adverse effects 3, 2

Alternative Approaches

• For patients who experience excessive sedation with hydroxyzine, consider:
  • Reducing the hydroxyzine dose to 10 mg at bedtime 2
  • Using cetirizine alone at 10 mg daily, which may be sufficient for many allergic conditions 3
  • For patients with severe allergic symptoms requiring higher antihistamine doses, cetirizine can be safely used at doses up to 20 mg daily, though this may increase sedation 3

By following this regimen and considerations, patients can benefit from 24-hour antihistamine coverage while minimizing daytime sedation and optimizing nighttime symptom control.