Penetration of moxalactam and cefazolin into bone following simultaneous bolus or infusion

The penetration of cefazolin and moxalactam into bone was studied in 20 adults scheduled for total hip arthroplasty. Patients randomly received both moxalactam and cefazolin (10 mg/kg of each) by either a rapid bolus or a 30-minute infusion. Serum and bone-extract concentrations were measured by HPLC. Serum concentrations of cefazolin were significantly greater than those of moxalactam at 15 minutes, 30 minutes, and at the time of bone removal for both rates of injection. Bone concentrations of cefazolin were significantly greater than those of moxalactam for both the bolus study (7.7 +/- 4.8 micrograms/g versus 5.4 +/- 3.4 micrograms/g) and the infusion study (5.6 +/- 3.4 micrograms/g versus 4.3 +/- 2.6 micrograms/g, respectively). There was no significant difference in the bone levels for the two drugs when penetration was expressed as a function of the simultaneous serum concentration (18% for each drug), and there were no significant differences in bone concentrations between the two rates of administration.