Pharmacokinetic comparison of 5 g of azlocillin every 8 h and 4 g every 6 h in healthy volunteers

To compare the multiple-dose pharmacokinetics of two dosage regimens of azlocillin, we studied 12 healthy volunteers via a randomized, crossover design with a 2-week washout phase between regimens. Serum and urine samples were collected for 8 h following the fifth dose of a regimen of 4 g every 6 h and the fourth dose of a regimen of 5 g every 8 h. Data for concentrations in serum were fitted to a two-compartment open model by nonlinear regression. Statistically significant differences (P less than 0.05) were observed in the following parameters (mean +/- standard deviation) for the 4- and 5-g regimens, respectively: area under the serum concentration-time curve during the dosing interval, 592 +/- 140 versus 772 +/- 151 micrograms.h/ml; terminal elimination rate constant, 0.5364 +/- 0.0912 versus 0.4758 +/- 0.0486 h-1; renal clearance, 87.6 +/- 16.1 versus 76.1 +/- 13.5 ml/min; maximum drug concentration in serum, 381 +/- 89 versus 473 +/- 90 micrograms/ml; and minimum drug concentration in serum, 19 +/- 10 versus 8 +/- 4 micrograms/ml. No significant differences were seen in the following parameters: V1, V beta, k10, k12, k21, total systemic clearance, and nonrenal clearance. These data support the presence of saturable renal elimination of azlocillin, as well as the feasibility of an 8-h dosing interval.