Rifampicin Diltiazem

Verapamil, diltiazem, erythromycin, and itraconazole all increase the plasma concentration of buspirone. The plasma concentration is decreased almost 10-fold by rifampicin. Grapefruit juice increases the overall subjective effect of the drug (Mahmood and Saha-jwalla, 1999). 

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. 

A study in 12 subjects found that the peak serum level following a single 120-mg oral dose of diltiazem alone was 186 nanograms/mL, but after taking rifampicin 600 mg daily for 8 days maximum serum diltiazem levels were less than 8 nanograms/mL. One patient with angina controlled with diltiazem 120 mg daily began to feel chest pain at rest one month af-... 

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-... 

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