Dosage Adjustments of Cefazolin According to the Pharmacokinetics of This New Cephalosporin

Serum and urine levels of cefazolin were studied: 1. following a single 500mg intra-muscular dose of the drug in normal subjects (n = 10), in patients with renal impairment (n = 12) and in patients undergoing maintenance hemodialysis (n = 10); 2. following a single 500 mg intra-venous dose of the drug in normal subjects (n = 10). In normal subjects, serum half-lives averaged 1.75 hour after intravenous injection (Ke = 0.395) and 2.22 hours after intra-muscular injection (Ke = 0.312); urinary recovery of cefazolin over a six hours period amounted to 61% after intra-venous injection and to 47.5% after intra-muscular injection. The renal clearance of the drug approximated 40 ml/mn. A linear correlation (Ke = 0.022 + 0.0028 CrCl) was established between the overall elimination rate-constants and the creatinine clearances in the subjects under investigation. The various pharmacokinetic constants thus obtained can be used to calculate the maintenance doses, loading doses and dosage intervals adjusted according to creatinine clearances. These data actually yield dosage regimes adapted to each individual case according to the degree of renal function.