Abstract

The excretory pattern for MK-196 is ocmpatible with that of other weak organic acids such as salicylate and probenecid. Tubular secretion of MK-196 is strongly inhibitied by probenecid and high loads of p-aminohippurate. Urinary excretion of MK-196 is increased 10-fold when the urine is alkaline. Clearances of MK-196 were not corrected for plasma protein binding of the drug which is very high (greater than 99%). Bidirectional transport processes are operative in that MK-196 is secreted by the renal tubule and passively back diffuses across the tubular epithelium by a pH-dependent process. MK-196 is able to overcome pyrazinoate-induced urate retention, whereas probenecid is not when studied by conventional clearance techniques. The uricosuric activity of MK-196 appears to be somewhat less with pyrazinoate than in its absence. When MK-196 is administered prior to pyrazinoate an attenuated uricosuric response was observed. This finding cannot be ascribed to a temporal decline in uricosuric action. Diuresis and saluresis produced by MK-196 are not influenced by pyrazinoate. The interaction of MK=196 and pyrazinoate on urate excretion is in direct contrast to results obtained with probenecid and pyrazinoate. A model has been proposed to explain this unique finding.