Nifedipine Rifampicin

Of all N Rs involved in xenobiotics metabolism induction, PX R is the most prominent one. PXR functions as a xenobiotic sensor and is activated by a large variety of chemically diverse compounds, for example lovastatin, nifedipine, rifampicin, SR12813, troglitazone or hyperforin (Chart 14.3), many of them standard therapeutic agents for common diseases [20-25]. 

Cardiac depressant effects may occur when verapamil or diltiazem is combined with a (p-adrenoceptor antagonoist or a cardiac glycoside. Nifedipine and verapamil are metabolised by cytochrome P-450 3A4. Inhibitors of this enzyme, e.g. HIV-protease inhibitors, cimetidine, fluoxetine, ketoconazole, erythromycin, will increase plasma levels and the dose should be carefully monitored. Conversely, enzyme inducers, e.g. carbamazepine, rifampicin, phenytoin, will decrease their plasma concentrations. 

Rifampicin markedly reduces the plasma levels of diltiazem, nifedipine, nilvadipine, verapamil and possibly reduces those of bamidipine, isradipine, lercanidipine, manidipine, nicardipine, nimodipine, and nisoldipine. They may become therapeutically ineffective unless the dose of the calcium-channel blocker is raised. Rifapentine and rifabutin would also be expected to reduce the levels of the calcium-channel blockers. 

The interactions between diltiazem, nifedipine, or verapamil and rifampicin are established and of clinical importance. There is some evidence that bamidipine, manidipine, nilvadipine, and nisoldipine interact with rifampicin and the manufacturers of a number of other calcium-chan-... 

Takasugi T. A case of hypertension suggesting nifedipine and rifampicin drug interaction. Igaku To Yakugaku (1989) 22, 132-5. 

Ndanusa BU, Mustapha A, Abdu-Aguye I. The effect of single dose of rifampicin on the pharmacokinetics of oral nifedipine. (1997) 15, 1571-5. 

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