DISPOSITION KINETICS OF TRIMETHOPRIM IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

1. The pharmacokinetics of trimethoprim (TMP) following intra-aortic a dministration were investigated in rainbow trout. 2. The disposition k inetics for TMP were best described by a three-compartment open model. The disappearance of TMP from fish blood was characterized by rapid a nd pronounced distribution phases and a slow terminal elimination phas e. 3. In contrast with pharmacokinetic data of TMP in mammals, the pre sent study documented a long terminal elimination t(1/2)(36.1 h), larg e V-dss(5980 ml/kg) and small Cl-b(2.4 ml/min/kg) for TMP in rainbow t rout, thus illustrating the slow biotransformation and elimination cap acity, particularly the strong 'holding' capacity (storage) for the dr ug in trout. 4. The pharmacokinetic profiles in the present study indi cated no dose dependency of TMP following three different bolus doses (5, 10 and 50 mg/kg). Hence, the first-order kinetic assumption was ve rified. 5. Urinary excretion of TMP was a minor elimination route in t rout (14.4% dose).