Biological fate of sirdalud in animals and man.

1. Biotransformation and excretion of the muscle relaxant drug, sirdalud, were studied after oral doses of 14C- and 3H-sirdalud in rats, dogs, rabbits, mice and humans. Sirdalud was well absorbed and almost completely metabolized in the five species. 2. Excretion of metabolites was rapid and complete within a few days; the urine/faeces excretion ratio of the 14C label was about 70/30 in all species. Major metabolic pathways of sirdalud were oxidative degradation of the imidazoline ring and oxidation of the aromatic system. 3. A novel oxidative biotransformation pathway of the benzothiadiazole ring system of sirdalud gave a sulphone analogue of the parent drug.