Objective: Two substrates were coadministered in a "cocktail" approach to evaluate the contribution of renal failure to drug oxidation.
Patients: Nineteen hypertensive patients, nine of them with chronic renal failure (CLCR 38.9 vs 102.3 ml.min-1 1.73 m-2), were investigated after peroral administration of a combination of antipyrine (500 mg, in capsules) and nifedipine (10 mg, in Oxcord capsules) in the morning after an overnight fast.
Results: This "cocktail" approach made it possible to characterize in vivo the activities of different forms of cytochrome P450 in a single-study protocol using the total clearance of nifedipine and clearance for production of 3-hydroxymethylantipyrine (HMA), 4-hydroxyantipyrine (OHA) and norantipyrine (NORA). With this "cocktail" approach (antipyrine plus nifedipine), we can suggest a selective effect on the activities of cytochrome P450 forms associated with the formation of dehydronifedipine (P450 III A4) and of NORA in patients with mild renal failure under long-term antihypertensive therapy.