The pharmacokinetics of chloramphenicol in the neonate and young infant.

The peak and trough serum concentrations and total body clearance of chloramphenicol were determined by microbiological assay in a multicentre investigation of 90 babies. Chloramphenicol was administered by the intravenous, intramuscular or oral route and dosage ranged between 12 and 210 mg/kg/day. A wide variation in both serum levels and clearance amongst babies receiving the same dose was observed. Neonates (64) had significantly higher serum concentrations (P less than 0.001) and slower clearance (P less than 0.0001) than infants (26). Oral administration in neonates resulted in lower steady state serum levels (P less than 0.02) than those following intravenous administration. Term neonates cleared chloramphenicol more rapidly than their preterm contemporaries (P less than 0.005). Forty-one per cent of subjects had potentially toxic serum levels; subtherapeutic peak serum levels (less than 15 mg/l) were recorded in 39/90 babies. Concomitant penicillin therapy resulted in higher serum concentrations (P less than 0.05); phenobarbitone was not associated with increased clearance or lower steady state serum levels of chloramphenicol. Postnatal age and gestational age accounted for some of the variability in pharmacokinetic response to chloramphenicol. Although many babies receiving the recommended dose had serum levels within the accepted range (15-25 mg/l), others did not. Routine monitoring of chloramphenicol in every baby receiving this antibiotic is essential: the regimens of 18% babies in the present study were altered after assay.