Adults

Adults and adolescents 12 years and older: 10 mg (10 mL) once daily. Children 6-11 years: 5 mg (5 mL) once daily or 2.5 mg (2.5 mL) twice daily. Children 2-5 years: 2.5 mg (2.5 mL) once daily; may be increased to a maximum of 5 mg (5 mL) daily, given as 2.5 mg every 12 hours.

Elderly

No dose adjustment generally required for elderly with normal renal function. For elderly with impaired renal function, dosage should be adjusted.

Renal_impairment

Moderate to severe renal impairment (creatinine clearance <50 mL/min): 5 mg (5 mL) once daily. Severe renal impairment (creatinine clearance <10 mL/min): not recommended.

Onset

Within 20-60 minutes

Excretion

Primarily excreted unchanged in urine (about 70%) and feces (about 10%).

Half life

Approximately 8-11 hours in adults; shorter in children (e.g., 6 hours in children 6-12 years).

Absorption

Rapidly absorbed from the gastrointestinal tract, peak plasma concentrations reached within 1 hour.

Metabolism

Undergoes limited hepatic metabolism (about 10-15%) to an inactive metabolite.

Theophylline

Small decrease in cetirizine clearance, but unlikely to be clinically significant.

Central nervous system depressants (e.g., alcohol, sedatives)

Increased risk of drowsiness and CNS depression.