Renal and biliary disposition of dapsone in the dog

Dapsone (4,4'-diaminodiphenylsulfone [DDS]) was administered intravenously to anesthetized dogs; urine was collected, heparinized venous blood was obtained, and bile was collected from some of the dogs. A constant infusion of inulin was maintained, and isosmotic or hypoosmotic fluids were administered. Dogs were studied under conditions of standardized, increased or decreased urine flow, and before and after plasmapheresis. Plasma, urine, and bile samples were analyzed for DDS and DDS conjugates; the degree of binding of DDS by plasma proteins was also determined. The renal clearances of inulin and DDS were calculated. No monoacetyldapsone (MADDS) was detected in the plasma, and only negligible quantities were found in the urine. Small quantities of DDS and DDS conjugates were detected in the bile in 4 h following the dose. Between 10 and 30% of the administered drug could be identified as DDS plus DDS conjugates in the urine in 8 h after the dose. Renal clearance of unbound DDS was proportional to the urine flow rate, and the clearance ratio of DDS to inulin approached the same maximal value as that for urea. Although the rate of urinary excretion of DDS conjugates was the same in the dog as in man, the rates of excretion of DDS and of DDS plus DDS conjugates were greater in the dog than in man, suggesting that the acetylation of DDS to MADDS by man but not by the dog and the greater degree of plasma protein binding of DDS and MADDS by man account for the longer half-time of disappearance of DDS in man compared to that in the dog.