A pharmacokinetic evaluation of the second-generation H1-receptor antagonist cetirizine in very young children.

The pharmacokinetics of the second-generation H1-receptor antagonist cetirizine was studied in eight children younger than 4 years of age who were treated with a single dose of cetirizine solution (5 mg). These children were hospitalized with suspected allergic respiratory problems or recurrent respiratory tract infections. Blood samples were collected at 1/2, 1, 1 1/2, 2, 4, 6, 8, 12, and 24 hours, and a 24-hour urine collection was performed in five of the samples. The findings obtained in children were compared with those obtained in 16 healthy young adults (mean +/- SD, 24.6 +/- 4.1 years) who received a single 20 mg dose. Cetirizine was absorbed more slowly in children (p = 0.006; mean +/- SD, 1.44 +/- 1.12 hours) than in adults (0.62 +/- 0.22 hours). The plasma elimination half-life of cetirizine was significantly shorter in children (p < 0.001; 4.91 +/- 0.6 hours) than in adults (8.6 +/- 2.1 hours), and the clearance rate was significantly higher in children (p < 0.001; 1.48 +/- 0.41 ml/min/kg) than in adults (0.80 +/- 0.17 ml/min/kg). Urinary excretion of unchanged cetirizine was significantly lower in children (p < 0.001; 37.8% +/- 5.2%; n = 5) than in adults (57.7% +/- 11.8%). Therefore the metabolism of cetirizine is faster in young children than in adults. This effect must be taken into account in future pharmacodynamic studies in this age group.