Pharmacokinetics of cefotaxime in neonates.

The effects of gestational age on the pharmacokinetics of cefotaxime and its desacetyl metabolite during the first days of life was investigated in a group of four full-term infants and 12 preterm infants of less than 35 weeks gestation. Half of the preterm infants had received betamethasone, a drug known to facilitate hepatic microsomal drug metabolism, whilst the others had not. No significant differences in the pharmacokinetics of cefotaxime were observed between the various groups, with elimination half-life (T 1/2 beta) of cefotaxime ranging from 4.04 +/- 1.52 to 4.56 +/- 1.31 h. The desacetyl metabolite of cefotaxime was present in all post-dose serum samples, irrespective of the gestational age of the baby. Its formation was apparently unaffected by prior exposure to betamethasone. The elimination half-life of cefotaxime is significantly longer in newborn infants than in older children or adults, this increase probably results from decreased renal excretion of the drug, rather than from immaturity in its metabolism. A dose of 50 mg/kg of cefotaxime given every 12 h is appropriate for infants of less than seven days old.