What is the recommended dosing for cetirizine (antihistamine)?

Cetirizine Dosing

The standard adult dose of cetirizine is 10 mg once daily, with dose reduction to 5 mg once daily required for moderate renal impairment (creatinine clearance 10-50 mL/min), and complete avoidance in severe renal impairment (creatinine clearance <10 mL/min). 1, 2

Standard Adult Dosing

• Adults and children ≥6 years: 10 mg once daily 1
• Do not exceed one 10 mg tablet in 24 hours 1
• A 5 mg dose may be appropriate for less severe symptoms 1
• Cetirizine has the shortest time to maximum concentration among second-generation antihistamines, reaching peak levels within 1 hour, which provides rapid symptom control when needed 2, 3

Dose Escalation for Refractory Cases

• For patients not responding to standard dosing, increase up to 40 mg daily (off-label, Quality of evidence III, Strength of recommendation C) 4, 2
• The British Association of Dermatologists supports this practice when potential benefits outweigh risks, particularly for chronic urticaria 4
• Higher doses (20-40 mg) may enhance "antiallergic" effects on mast-cell mediator release 4

Renal Impairment Adjustments

• Moderate renal impairment (CrCl 10-50 mL/min): Reduce dose to 5 mg once daily 4, 2
• Severe renal impairment (CrCl <10 mL/min): Avoid cetirizine entirely 4, 2
• Cetirizine is predominantly eliminated by renal excretion with a mean half-life of 8.3 hours, making dose adjustment critical 2, 3

Special Populations

Elderly (≥65 years)

• Consult a physician before use 1
• Consider starting with 5 mg daily due to potential age-related decline in renal function 1

Children <6 years

• Consult a physician 1
• Not recommended for infants under 6 months 5
• For infants 6-11 months, oral drops are available for precise dosing 2

Pregnancy and Lactation

• Avoid all antihistamines during pregnancy, especially first trimester, though cetirizine is FDA Pregnancy Category B (no evidence of fetal harm but well-controlled human studies lacking) 4, 2
• Chlorphenamine is often preferred in the UK when antihistamine therapy is necessary due to its long safety record 4

Hepatic Impairment

• No specific dose adjustment required, as cetirizine undergoes minimal hepatic metabolism 6
• Consult a physician 1

Timing and Administration

• Evening dosing may be preferable if sedation occurs, ensuring highest drug levels when symptoms are anticipated 2
• Cetirizine may cause sedation in approximately 13.7% of patients (vs. 6.3% with placebo), particularly at higher doses 2, 7
• Adjust timing to ensure peak drug levels coincide with anticipated symptom onset 4

Common Pitfalls to Avoid

• Do not combine with other sedating medications without considering additive CNS effects 2
• Do not assume "second-generation" means zero sedation risk—cetirizine carries meaningful sedation potential even at standard 10 mg doses 7
• Patients with low body mass may experience elevated drug levels (mg/kg basis) with standard dosing, potentially causing drowsiness 7
• Do not use in severe renal impairment—this is a critical contraindication 4, 2

Drug Interactions

• Cetirizine has negligible interaction with hepatic enzymes and no significant drug interactions reported 3, 6
• No cardiac toxicity or QT prolongation concerns (unlike mizolastine) 4
• High oral bioavailability (>70%) with minimal first-pass metabolism 6