The pharmacokinetics of lisuride hydrogen maleate in rat, rabbit and rhesus monkey

The pharmacokinetics of lisuride hydrogen maleate (LHM) were investigated in rat, rabbit and rhesus monkey. Experiments were designed to meet not only the requirements of drug registration but also to serve other preclinical disciplines (toxicology, pharmacology). LHM is absorbed almost completely at a dose level of 100-250 micrograms/kg. During absorption and first liver passage (FPE) LHM is metabolized. The FPE was highest in the rhesus monkey and lowest in the rat. Calculated on bioavailability during chronic tolerance studies, in the highest dose group rats were burdened with 180-fold and rhesus monkeys with 70-fold the highest human dose (parkinsonism). Total clearance values indicated the presence of extrahepatic metabolism in all animal species. Terminal half-lives of unchanged drug in plasma were in the range of a few hours. Therefore, no accumulation of unchanged drug was expected to occur following daily repeated administration in the animal species investigated. Elimination of 14C-radioactivity proceeded mainly via the liver in rat and rabbit. The rhesus monkey excreted most of the dose administered in the urine. Enterohepatic circulation of 14C-material was demonstrated in the rat. In the rat but not in the other two species a small part of the dose (about 2%) accumulated in blood cells in the form of metabolites. Unchanged lisuride is able to cross membranes very rapidly, this was shown in distribution studies (whole-body autoradiography of rat, direct measurements in rat and rabbit). Transfer of lisuride into fetuses and brain is governed by its concentration in plasma. Drug level decrease in fetuses and brain was shown to somewhat slower than in plasma. Detailed evaluation of the distribution pattern in the brain of rat and rabbit showed a high affinity of lisuride for its preferential target tissue, the pituitary.