¹The Hospital Bulovka, Prague, Czech Republic; the Free University (VUB) and the Catholic University Louvain (UCL), Brussels, Belgium; and the UCB s.a. Pharma Sector, Braine-l'Alleud, Belgium.

Correspondence: Réginald Hulhoven, MD, PhD, UCB s.a. Pharma Sector, Chemin du Foriest, B 1420 Braine-l'Alleud, Belgium.

^†Deceased.

^*Supported by the MDI department of UCB s.a., Pharma Sector, Braine-l'Alleud, Belgium.

Received 10 April 1996; Accepted 6 September 1996.

Abstract

The pharmacokinetics of the second-generation H₁-receptor antagonist cetirizine were studied in 15 infants and toddlers (mean SD age, 12.3 5.4 months) who were treated with a single 0.25 mg/kg dose of cetirizine solution. The infants and toddlers were hospitalized for recurrent respiratory infections or other hypersensitivity-related diseases. Blood samples were collected at ½, 1, 1½, 2, 4, 6, 8, 12, and 24 hours, and a 24-hour urine sample was obtained. A peak plasma level of 390 135 ng/ml was observed after 2.0 1.3 hours. The elimination half-life was 3.1 1.8 hours, the apparent oral body clearance was 2.13 1.15 ml/min/kg, and the apparent volume of distribution 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 toddlers, after the intake of 0.25 mg/kg cetirizine twice a day for at least 4 days. A 90% 12% inhibition of the wheal and a 87% 17% inhibition of the flare were still observed 12 hours after the last intake. The duration of the H₁-inhibition by cetirizine at the cutaneous level is thus longer in infants and toddlers than could be inferred from its pharmacokinetics; the level of inhibition at 12 hours was the same as in older age groups.