Comparison of serum concentrations of ceftazidime and tobramycin in newborn infants.

Peak and trough serum concentrations of ceftazidime and tobramycin were determined in neonates with suspected septicaemia in an open randomized study. Mean peak serum levels were 85 (+/- 4.4 SE) mg/l for ceftazidime and 5.8 (+/- 0.3 SE) mg/l for tobramycin. The peak serum levels of ceftazidime were well above the reported minimal inhibitory concentration (MIC)90 values of pathogenic bacteria encountered in neonates, while peak serum levels of tobramycin were lower than reported MIC90 values for Klebsiella, Pseudomonas, Enterobacter and Serratia species. Nine of 33 tobramycin-treated patients had potentially toxic trough serum levels (greater than 2 mg/l) and nine had subtherapeutic peak serum levels (less than 4 mg/l). The dosage of this antibiotic had to be changed frequently. In comparison only 2 of 29 ceftazidime-treated patients had subtherapeutic peak levels (less than 40 mg/l) and none had potentially toxic trough levels (greater than 40 mg/l). Ceftazidime, in comparison with tobramycin, has a more favourable antibacterial spectrum and routine determinations of peak and trough serum levels should not be necessary.