Penetration of Cephazolin in Human Lumbar Intervertebral Disc

Abstract

Levels of the antibiotic cephazolin were measured in disc and blood from a consecutive series of patients undergoing lumbar spinal fusion. To determine if levels of cephazolin in the human disc reach the stated minimum inhibitory concentration against Staphylococcus aureus (1 mg/L) following intravenous administration, and to determine if there is a therapeutic relationship between serum concentration and disc concentration. Disc space infection is a potential complication of surgical procedures that violates the intervertebral disc. Bacteria, often from normal skin flora, can be introduced into the disc space causing inflammation with destruction of the adjacent vertebral endplate. Although there is substantial evidence from animal studies that prophylactic antibiotics reduce the incidence of discitis, similar evidence in human beings is not strong. A total of 30 patients, including 15 females and 15 males, with a mean age 42 years (range 21-63), received 1-g cephazolin (intravenous) during 1 or 2-level lumbar spinal fusion surgery. Venous blood was collected before administration of cephazolin and again at disc removal. Disc cephazolin concentrations were measured at the same time serum levels were measured for each patient. The interval between cephazolin administration and tissue sampling ranged from 7 to 137 minutes. Cephazolin concentration in the serum (range 31.1-148 mg/L) was higher than in the disc (range 0-9.5 mg/L). The concentration of cephazolin peaked in the serum at 7 minutes, and in the disc between 37 and 53 minutes. More than 70% of the disc samples had detectable levels of cephazolin at the time the disc was removed, although only half of these samples had cephazolin levels higher than 1 mg/L. All serum cephazolin concentrations were higher than 1 mg/L. Serum cephazolin concentration did not relate to disc concentration at a given time. The time when antibiotic concentration is highest in the disc varies among patients. More than 70% of disc samples had detectable levels of cephazolin, although only half of the discs contained cephazolin higher than the stated minimum inhibitory concentration for S. aureus(>1 mg/L). Factors such as molecular charge, degree of disc degeneration, and disc size may influence antibiotic penetration into the disc.