Clinical pharmacokinetics in infants and children.

Wide variations in drug dose recommendations for children of the same or different ages reflect the inadequacy of data on pharmacokinetics and pharmacodynamics in children. Selected aspects of available literature on pharmacokinetics of drugs used in older infants and children has been reviewed with special attention to calculation of an age-appropriate dose. During the neonatal period and early infancy the elimination of many drugs that are excreted in the urine in unchanged form is restricted by the immaturity of glomerular filtration and renal tubular secretion. On the other hand, in late infancy and/or in childhood, a similar or greater rate of elimination from plasma than in adults has been observed for many drugs, notably digoxin, phenobarbitone, phenytoin, carbamazepine, ethosuximide, diazoxide, clindamycin and propoxyphene. Consistent with this, it has been shown that some drugs exhibit a lower plasma level/dose ratio in infancy and early childhood as compared with the adult. This is true for phenobarbitone, phenytoin and ethosuximide. Some age groups of children remain uninvestigated with regard to pharmacokinetics, even for the drugs reviewed. Therefore, pediatric therapy remains empirically based for many drugs.