PHARMACOKINETICS AND PHARMACODYNAMICS OF CETIRIZINE IN INFANTS AND TODDLERS

The pharmacokinetics of the second-generation H-1-receptor antagonist cetirizine were studied in 15 infants and toddlers (mean +/- SD age, 1 2.3 +/- 5.4 months) who were treated with a single 0.25 mg/kg dose of cetirizine solution. The infants and toddlers were hospitalized for re current respiratory infections or other hypersensitivity-related disea ses. Blood samples were collected at 1/2, 1, 11/2, 2, 4, 6, 8, 12, and 24 hours, and a 24-hour urine sample was obtained. A peak plasma leve l of 390 +/- 135 ng/ml was observed after 2.0 +/- 1.3 hours. The elimi nation half-life was 3.1 +/- 1.8 hours, the apparent oral body clearan ce was 2.13 +/- 1.15 ml/min/kg, and the apparent volume of distributio n was 0.44 +/- 0.19 L/kg. The excretion of unchanged cetirizine in six complete urinary collections was 62.7% +/- 13.2% of the administered dose. An additional pharmacodynamic study (inhibition of the histamine -induced wheal and flare) was performed in 10 of these infants and tod dlers, after the intake of 0.25 mg/kg cetirizine twice a day for at le ast 4 days. A 90% +/- 12% inhibition of the wheal and a 87% +/- 17% in hibition of the flare were still observed 12 hours after the last inta ke. The duration of the H-1-inhibition by cetirizine at the cutaneous level is thus longer in infants and toddlers than could be inferred fr om its pharmacokinetics; the level of inhibition at 12 hours was the s ame as in older age groups.