Is it safe to prescribe Zyrtec (cetirizine) twice a day?

Prescribing Zyrtec (Cetirizine) Twice Daily

Zyrtec (cetirizine) should not be prescribed twice daily as the FDA-approved dosing is one 10 mg tablet once daily, with instructions not to take more than one 10 mg tablet in 24 hours. 1

Standard Dosing Guidelines

• The FDA-approved dosing for cetirizine in adults and children 6 years and over is one 10 mg tablet once daily, with explicit instructions not to exceed this dose within a 24-hour period 1
• For less severe symptoms, a 5 mg product may be appropriate, but this still maintains the once-daily dosing schedule 1
• Special populations requiring dosage adjustments include:
  • Adults 65 years and over: Consult with a doctor before use 1
  • Children under 6 years: Consult with a doctor before use 1
  • Patients with liver or kidney disease: Require physician evaluation for potential dose adjustment 1

Safety Considerations

• Cetirizine is designed for once-daily administration due to its pharmacokinetic profile and long duration of action 2
• While cetirizine has a favorable safety profile compared to first-generation antihistamines, increasing the dose beyond FDA recommendations may increase the risk of side effects 3
• Common adverse effects of cetirizine include:
  • Sedation (though less than first-generation antihistamines) 2
  • Gastrointestinal disturbances 3
  • Potential for increased sedation at higher doses 2

Alternative Approaches for Inadequate Symptom Control

If a patient is not responding adequately to the standard once-daily 10 mg dose of cetirizine, consider these options instead of twice-daily dosing:

• Increase to a single 20 mg daily dose (off-label) which has shown efficacy in patients with urticaria resistant to standard dosing 4
• Switch to a different antihistamine, such as loratadine or fexofenadine 5
• Add a sedating antihistamine at night (e.g., chlorphenamine 4-12 mg or hydroxyzine 10-50 mg) to a non-sedating antihistamine during the day for better symptom control 5
• Consider the addition of an H2 antihistamine which may provide better control of urticaria than an H1 antihistamine alone 5

Research on Higher Dosing

• A study on patients with urticaria resistant to standard cetirizine dosing found that doubling the dose to 20 mg once daily (not twice daily) was effective in improving symptoms 4
• Another study comparing 10 mg once daily versus 10 mg twice daily in severe seasonal allergic rhinoconjunctivitis found no significant differences in efficacy between the two dosing regimens, except for sneezing and sedation 6
• The increased sedation with higher doses may compromise the non-sedating benefits that make cetirizine preferable to first-generation antihistamines 2

Common Prescribing Pitfalls

• Prescribing twice-daily dosing contradicts FDA labeling and may increase the risk of adverse effects without proportional increase in therapeutic benefit 1, 3
• Failing to consider alternative antihistamines when cetirizine at standard doses is ineffective 5
• Not recognizing that patients with liver or kidney disease may require dosage adjustments, making twice-daily high-dose regimens particularly problematic 1