DISTRIBUTION OF INTRAMUSCULARLY ADMINISTERED ERYTHROMYCIN INTO SUBCUTANEOUS TISSUE CHAMBERS BEFORE AND AFTER INOCULATION WITH PASTEURELLA-HAEMOLYTICA

Distribution of erythromycin into subcutaneous tissue chambers was cha racterised pharmacokinetically and the effect of Pasteurella haemolyti ca infection on the extent of penetration was studied. Thermoplastic t issue chambers were implanted subcutaneously in the paralumbar fossae of six calves. Thirty-five days after implantation, the tissue chamber distribution of intramuscularly administered erythromycin (30 mg kg-1 ) was studied. Chambers were then inoculated with P haemolytica and th e tissue chamber pharmacokinetics of erythromycin were again studied. Diffusion of erythromycin into tissue chambers was best described usin g a two-compartment model with tissue chambers representing a relative ly inaccessible compartment. Despite changes in chamber fluid pH, the extent of erythromycin penetration into chambers was not affected by P haemolytica inoculation. Comparison of computer simulated concentrati on-time curves resulting from different routes of administration revea led that penetration of erythromycin into less accessible sites was mo re likely to be higher after intravenous administration than after int ramuscular administration.