Increase of thiopental concentration in rat tissues due to anesthesia with isoflurane

Thiopental distribution was studied in rats (30 mg/kg i.v.) anesthetized simultaneously with 1.25 "rat"-MAC isoflurane. The thiopental concentration in serum and several tissues was determined UV-photometrically at 305 nm after extraction and TLC. In the serum of rats anesthetized with isoflurane the thiopental concentration was significantly increased to +39----+74% in comparison to controls during 30 min following the barbiturate injection. Also in liver, brain, heart, kidney, lung and spleen of rats anesthetized with isoflurane the thiopental concentration was significantly increased at 3 and 10 min; at 30 min the difference vs. control had vanished in brain, heart, lung and spleen. Obviously, thiopental was transiently "trapped" during the early distribution phase to a considerable amount in these vessel-rich tissues when anesthesia with isoflurane was simultaneously performed; this pharmacokinetic interaction might be explained at least to some extent hemodynamically; in many tissues regional blood flow is reduced during anesthesia with isoflurane; thereby the "washout" of thiopental from the tissues and the redistribution are delayed.