Hepatic mixed function oxidase induction during rifampicin/isoniazid therapy in Indian vegetarians

To determine the effect of rifampicin therapy on hepatic oxidase activity in animal protein deficient patients antipyrine and quinine t 1/2 and 6B-hydroxycortisol (6B-OHF) excretion was studied in 8 Indian vegetarians during treatment for tuberculosis. In 4 patients at the start of treatment rifampicin/streptomycin caused a steady decline in by time antipyrine t 1/2 which was complete in 3 weeks, in one patient introduction of isoniazid produced a temporary reversal. After 4 months rifampicin/isoniazid 6B-OHF excretion was increased 2 to 10 fold in all patients although one followed serially showed a marked fall when isoniazid was begun. Decline in antipyrine t 1/2 persisted in 4 patients at the end of 18 months therapy and in one of these concurrent quinine t 1/2 confirmed partial isoniazid reversal of this decline. Rifampicin-mediated mixed function oxidase induction appeared similar to that reported for non-vegetarians and largely persists with combination therapy throughout treatment. Isoniazid can act as a competitive inhibitor of hepatic oxidase activity in some patients.