Reversal of sulfamerazine inhibition of rat hepatic uroporphyrinogen synthesis by folic acid.

The ability of rat hepatic uroporphyrinogen cosynthase to direct formation of uroporphyrinogen III and the synthesis of uroporphyrinogen in vitro was impaired by sulfamerazine. Inhibition was reversed by the addition of folic acid. Administration of a single, oral dose (1 g/kg) of sulfamerazine to rats was associated with elevated levels of hepatic uroporphyrin I isomer. These results suggest that sulfonamides may interfere with the biosynthesis of uroporphyrinogen III.