Evidence for a dual action of sulphinpyrazone on drug metabolism in man: theophylline‐sulphinpyrazone interaction.

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Abstract
The effects of sulphinpyrazone administration on the metabolic and renal clearances of theophylline in man were investigated. Sulphinpyrazone increased total plasma theophylline clearance by 22%. This was the sum of increases in metabolic clearances by 3- demethylation (32%), 1-demethylation (30%) and 8-oxidation (22%) and of a decrease in renal clearance (27%). It is proposed that sulphinpyrazone has differential effects on at least two forms of cytochrome P-450 inhibiting one enzyme or group of enzymes which metabolises tolbutamide, phenytoin and S(-)warfarin and inducing a form (or forms) which metabolises theophylline, antipyrine and R(+)warfarin.