Forecasting cephalosporin and monobactam antibiotic half-lives in humans from data collected in laboratory animals.

The postdistribution half-lives of 10 cephalosporin and 2 monobactam antibiotics in humans were predicted from data obtained in other mammals. This forecasting was accomplished with the allometric equation t1/2 = aWb, where a is the y intercept and b is the slope obtained from the log-log plot of antibiotic half-life (t1/2) versus body weight (W). Dimensionless similarity criteria were used to produce a biological clock for ceftizoxime elimination. The creation of the biological clock, which measured physiologic time (heartbeats) rather than chronologic time (minutes), demonstrated that ceftizoxime half-life was identical in five mammals. This methodology will contribute to infectious disease research through a greater understanding of pharmacokinetic scaling in mammals.