[Pharmacokinetic properties of rithmidazole upon single intravenous introduction]

The kinetics of rithmidazole (an imidazobenzimiodazole derivative possessing the properties of I, III, and IV class antiarrhythmics) was studied upon a single intravenous introduction in rats (in a dose of 10 mg/kg) and in healthy male volunteers (300 mg/kg). The drug pharmacokinetics in rat blood plasma was characterized by rapid elimination from the systemic blood flow (drug detected by HPLC only within 6 h); the total plasma clearance was 1.43 liter/(h kg), the terminal half-elimination time was 1.76 h, and the equilibrium distribution volume (2.42 liter/kg) exceeded the total volume of water in the animal organism, which is indicative of a high level of absorption in tissues. The drug is characterized by a low level of binding to blood proteins and erythrocytes. Investigation of the drug distribution between tissues showed evidence of extensive, blood-flow-dependent penetration, with the drug concentration in most tissues exceeding that in the blood plasma. The maximum amounts of rithmidazole were found in the lungs, spleen, liver, and kidneys. The major excretion route for the unchanged drug is via urine and bile, amounting to 10% and approximately 1% of the dose introduced, respectively, determined within 72 h. The results are indicative of a low probability of the hepatoduodenal circulation of the unchanged substance: about 90% of the drug undergo metabolic transformation. The pharmacokinetics of rithmidazole in volunteers was also characterized by rapid elimination from the systemic blood flow; the total plasma clearance was 0.89 liter/(h kg), the terminal half-elimination time was 2.12 h, and the equilibrium distribution volume was 1.66 liter/kg. The obtained results show that the pharmacokinetic profiles of rithmidazole in rats and humans exhibit a similar character, with a high intensity of distribution and elimination processes.