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 pulpo sus. Objectives. The purpose of the study was to investigate the pharm acokinetics of gentamicin penetration into normal rabbit nucleus pulpo sus. Summary of Background Data. Disc space infection is a complicatio n of spinal surgery that can be prevented by prophylactic antibiotics. Gentamicin can be used in conjunction with other antibiotics as a pro phylactic agent. One previous study demonstrated that a similar antibi otic, tobramycin, penetrates the disc, but no data have been reported on the pharmacokinetics of disc penetration. Methods. Twenty-four rabb its were given an intravenous injection of gentamicin labeled with iod ine 125. Four rabbits were killed at hourly intervals 1 to 6 hours aft er injection. Specimens of nucleus pulposus, blood, whole liver, and s aline-perfused liver were obtained and prepared. The radioactivity in the specimens was measured. Results. The gentamicin concentration in t he nucleus pulposus peaked at 2 hours and remained at this level for t he duration of the experiment. Twenty percent of the gentamicin recove red from the nucleus pulposus was tissue bound. Conclusions. Gentamici n concentration in the rabbit nucleus pulposus does not peak until 2 h ours after an intravenous bolus of drug. If gentamicin penetrates huma n nucleus pulposus in a similar fashion, this study could have implica tions for the timing of administration of this agent for prophylaxis.