Gentamicin penetration into normal rabbit nucleus pulposus.

STUDY DESIGN

Radioactively labeled gentamicin was administered to 24 rabbits to assess the concentration of antibiotic in the nucleus pulposus.

OBJECTIVES

The purpose of the study was to investigate the pharmacokinetics of gentamicin penetration into normal rabbit nucleus pulposus.

SUMMARY OF BACKGROUND DATA

Disc space infection is a complication of spinal surgery that can be prevented by prophylactic antibiotics. Gentamicin can be used in conjunction with other antibiotics as a prophylactic agent. One previous study demonstrated that a similar antibiotic, tobramycin, penetrates the disc, but no data have been reported on the pharmacokinetics of disc penetration.

METHODS

Twenty-four rabbits were given an intravenous injection of gentamicin labeled with iodine 125. Four rabbits were killed at hourly intervals 1 to 6 hours after injection. Specimens of nucleus pulposus, blood, whole liver, and saline-perfused liver were obtained and prepared. The radioactivity in the specimens was measured.

RESULTS

The gentamicin concentration in the nucleus pulposus peaked at 2 hours and remained at this level for the duration of the experiment. Twenty percent of the gentamicin recovered from the nucleus pulposus was tissue bound.

CONCLUSIONS

Gentamicin concentration in the rabbit nucleus pulposus does not peak until 2 hours after an intravenous bolus of drug. If gentamicin penetrates human nucleus pulposus in a similar fashion, this study could have implications for the timing of administration of this agent for prophylaxis.