Transformation and Excretion of Drugs in Biological Systems. VI. Correlation between Renal Excretion and Biotransformation of Sulfisomidine and Sulfamethizole

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Sulfisomidine, sulfamethizole and their biotransformed products in man (N⁴-acetate, N⁴-glucuronide, N4-sulfonate) were applied to renal clearance experiments in dogs and protein binding experiments to dog plasma protein in order to elucidate their renal excretion mechanisms.
Clearance ratio of N⁴-acetate of both sulfonamides were less than that of original sulfonamides. From the results of inhibitory experiments by iodopyracet, it was found that both sulfonamides and their N⁴-acetates were actively secreted and N⁴-glucuronides exhibited reduced proximal tubular secretion. It was observed that clearance ratio of sulfamethizole-N⁴-glucuronide, in spite of the reduced affinity for plasma protein and increased solubility, were lower than that of sulfamethizole.