A review of the pharmacokinetics and metabolism of sulfadimethoxine in the rainbow trout (Salmo gairdneri).

The pharmacokinetics and metabolism of sulfadimethoxine (SDM) was examined in the rainbow trout. Results from pharmacokinetic studies indicate a lengthening of the SDM half-life when administration was shifted from single to a multiple dose regime. In contrast to mammals and similar to the catfish a low magnitude nonspecific plasma protein binding was evident with SDM. Volume of distribution data indicates that SDM is distributed in plasma, extracellular and to a limited degree, intracellular fluid spaces. This distribution was greater than that demonstrated for mammals; however, lower than for the lobster or catfish. Absorption of SDM from the trout gastrointestinal tract varied with chemical form and dosage. Lower relative bioavailability values were evident with crystalline SDM and with high doses of the sodium salt. SDM accumulated to the highest levels in the bile followed by the intestine, liver, blood, skin, kidney, spleen, gill, muscle and fat respectively. Biliary SDM was composed of parent, N-acetylated SDM, an unknown polar metabolite, and what appears to be a sulfate conjugate.