Protein binding ability of various antimicrobial drugs in neonates

We evaluated the influence of albumin on protein binding of antimicrobial drugs most widely used in neonates and the possible correlation between protein binding and gestational weeks or birth weight. Protein binding of ampicillin (ABPC) in neonates was not associated with the amount of albumin, and was slightly higher than that in adults. Protein binding of cefotaxime (CTX), flomoxef (FMOX), cetrazidime (CAZ), cefozopran (CZOP), ceftriaxone (CTRX), and aztreonam (AZT) were similar to or lower than those in adults reported in the literature. Protein binding was compared between neonates born < 37 weeks of gestation and those born ≧ 37 weeks of gestation. Protein binding of CTX was significantly lower in neonates born < 37 weeks of gestation (19.7%) than in those born ≧37 weeks of gestation (30.2%), but protein binding of other drugs did not differ markedly between groups. Protein binding was also compared between neonates with birth weights of <2,500 g and ≧ 2,500 g. Protein binding did not differ significantly for any drug between groups. Evaluation by gestational week or birth weight showed lower protein binding in premature neonates and low birth-weight neonates than in adults. Pharmacokinetic parameters evaluated in this study suggest that an increase in the plasma drug-free form ratio does not affect the effectiveness or safety of antimicrobial drugs.