A pharmacokinetic/pharmacodynamic (PK/PD) approach was used to determine a dosage regimen of cephalothin (CET) after intramuscular (IM) administration in horses. CET plasma concentrations were measured in eight horses after a single IM administration of 11 mg/kg bwt of CET. The data were modeled using a nonlinear mixed-effect model, and the probability of target attainment (PTA) of the PK/PD target was calculated for 5,000 horses generated by Monte Carlo simulations. IM administrations of CET at 11 mg/kg bwt q 8 hr and q 6 hr achieved a PTA of 90% against the MIC90 of S. zooepidemicus and S. aureus, respectively, and were considered to be effective dosage regimens. The total dose for the IM administration recommended in this study was lower than that for intravenous (IV) administration in previous studies.
Keywords: cephalosporins; gram-positive bacteria; intramuscular administration; pharmacokinetics.
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