Pharmacokinetics of sulphadimethoxine in the lobster, Homarus americanus, following intrapericardial administration

Abstract

1. The pharmacokinetics and tissue distribution of intrapericardially administered sulphadimethoxine were studied in the lobster Homarus americanus. 2. Pharmacokinetic analysis of haemolymph concentration-time data indicated that a two compartment model best described sulphadimethoxine disposition, and that there were no apparent sex differences in the lobster. Analysis of total body clearance (Clb), apparent steady-state volume of distribution (Vss), area under the curve, and plasma protein binding in lobsters receiving 21, 42 and 55 mg/kg sodium sulphadimethoxine indicated that the pharmacokinetics were independent of dose. 3. Mean parameter estimates for Clb, Vss, and terminal half life were 13.8 ml/h/kg, 1369 ml/kg, and 76.7 h, respectively. Binding of sulphadimethoxine to haemolymph proteins was linear, with a mean of 53.5% bound. 4. Analysis of the tissue distribution of radiolabelled sulphadimethoxine at 4, 48 and 336 hours after a 42 mg/kg dose indicated that sulphadimethoxine was excreted slowly by the lobster, with the muscle, shell and haemolymph holding the largest fraction of the dose at early times. After 2 weeks, 9.5% of the radiolabel remained in the animal, with the hepatopancreas and digestive tract holding the greatest concentration of the dose.