[Pharmacokinetic effect of various antibiotics in the tissues]

The tissular pharmacokinetics of antibiotics were studied by sacrificing rats in groups of 6 at various intervals after the injection of ampicillin, cephalothin, doxycycline, gentamicin and sisomicin. A microbiological method was used to determine levels in 10 organs. The antibiotic penetrated rapidly into all the tissues but with very different affinities depending on the organ involved. The concentration of doxycycline in the tissues was always higher than in the serum and this relationship was maintained throughout the investigation. This was not true of ampicillin which disappeared a little more slowly from the organs, particularly the renal medulla, than from the serum. The aminosides showed a marked accumulation and prolonged persistence in the renal cortex: 4 weeks after injection concentrations were found which were above the maximum levels in the serum. When daily injections of 4 mg/kg aminoside were given, concentrations above 350 mug/g were found after 7 days. These findings permit a better understanding of antibiotic effectiveness and toxicity.