Cimetidine pharmacokinetics and dosage requirements in children

The pharmacokinetics of cimetidine (10 mg/kg) were investigated in 11 children following an oral dose and in 9 children following an intravenous dose. The children ranged in age from 4-13 years and were undergoing radiology for upper gastrointestinal tract pain. Compared with a group of adults, the children had a higher total body clearance (11.6 +/- 3.4 versus 7.0 +/- 2.5 ml/min per kg; P less than 0.005), a larger apparent volume of distribution (1.24 +/- 0.40 versus 0.80 +/- 0.24 l/kg; P less than 0.005) and a shorter elimination half-life (83 +/- 26 versus 122 +/- 16 min; P less than 0.001) of cimetidine. Renal clearance in children comprised 70% of total body clearance, more than double that of adults (9.0 +/- 1.9 versus 4.2 +/- 2.1 ml/min per kg; P less than 0.001). The area under the cimetidine plasma concentration: time curve after the oral dose was on average 42% in children compared with adults. The mechanism for the increased elimination of cimetidine in children is suggested to be an increase in the renal tubular secretory transport of cimetidine in the kidney. A statistically significant negative correlation was observed between age and cimetidine renal clearance. A cimetidine dosage regimen of approximately 30 mg/kg per day in three to four divided doses would be an appropriate dose in children.