Pharmacokinetics of sulfamethazine in buffaloes

Pharmacokinetic parameters which describe distribution and elimination of sulfamethazine were determined in buffaloes. Following intravenous administration of a single dose (100 mg/kg), disposition of the drug was described in terms of biexponential expression: Cp = Ae alpha t + Be-beta t. Based on total (free and bound) sulfonamide levels in the plasma, pseudo-distribution equilibrium was rapidly attained and the half-life value of 5.54 +/- 0.41 h (mean +/- S.D., n = 8) was recorded. Body clearance was 56 +/- 7 ml x kg-1 x h-1. Based on this study we suggest an intravenous dosage regimen consisting of 38.4 mg sulfamethazine/kg body-weight repeated at 12 h inrervals. With this dosage level the predicted plasma concentrations will oscillate between 125 and 25 micrograms/ml during the steady-state. The influence of febrile states and bacterial diseases on predicted levels remains to be verified experimentally.