Atazanavir Verapamil

Others Acetaminophen, amiodarone, carbamazepine, delavirdine, efavirenz, nevirapine, quinidine, repaglinide, sildenafil, tadalafil, trazodone, vardenafil Amiodarone, amprenavir, atazanavir, ciprofloxacin, cisapride, clarithromycin, diltiozem, erythromycin, fluconazole, fluvoxamine, grapefruit juice (in high ingestion), indinavir, itraconazole, ketoconazole, nefazodone, nelfinavir, norfloxacin, ritonavir, telithromycin, troleandomycin, verapamil, voriconazole Carbamazepine, efavirenz, glucocorticoids, macrolide antibiotics, nevirapine, phenytoin, phenobarbital, rifabutin, rifapentine, rifampin, St. John s wort... 

Drugs that may inhibit cytochrome P450 metabolism of other drugs include amiodarone, androgens, atazanavir, chloramphenicol, cimetidine, ciprofloxacin, clarithromycin, cyclosporine, delavirdine, diltiazem, diphenhydramine, disulfiram, enoxacin, erythromycin, fluconazole, fluoxetine, fluvoxamine, furanocoumarins (substances in grapefruit juice), indinavir, isoniazid, itraconazole, ketoconazole, metronidazole, mexile-tine, miconazole, nefazodone, omeprazole, paroxetine, propoxyphene, quinidine, ritonavir, sulfamethizole, verapamil, voriconazole, zafirlukast, and zileuton. 

A Atazanavir, clarithromycin, indinavir, itraconazole, ketoconazole, nefazodone, nelfinavir, ritonavir, saquinavir, telithromycin Amprenavir, aprepitant, diltiazem, erythromycin, fluconazole, fosamprenavir, grapefruit juice", verapamil Cimetidine... 

Clinically important, potentially hazardous interactions with atazanavir, chlorpromazine, cimetidine, co-trimoxazole, degarelix, fluphenazine, ketoconazole, medroxyprogesterone, megestrol, mesoridazine, phenothiazines, prochlorperazine, progestins, promethazine, ranolazine, thioridazine, trifluoperazine, trimethoprim, verapamil, zuclopenthixol... 

Clinically important, potentially hazardous interactions with atazanavir, azithromycin, bosentan, cholestyramine, clarithromycin, cyclosporine, darunavir, delavirdine, erythromycin, exenatide, fenofibrate, fosamprenavir, gemfibrozil, grapefruit juice, imatinib, itraconazole, red rice yeast, tacrolimus, telithromycin, tipranavir, tolvaptan, verapamil... 

Protease inhibitors, particularly ritonavir (see Antivirals , (p.772)), are potent inhibitors of cytochrome P450 isoenzyme CYP3A4, by which all the calcium-channel blockers are extensively metabolised. It appears that some protease inhibitors can cause a clinically relevant increase in calcium-channel blocker levels. In addition, verapamil, diltiazem and nicardipine can also inhibit CYP3A4, and might therefore theoretically reduce the metabolism of the protease inhibitors. However, the effect might depend on which is the more potent inhibitor, since, in the studies above, diltiazem did not affect atazanavir, indinavir or ritonavir levels. 

Although information is limited, these pharmacokinetic interactions are predictable, and potentially serious. To date, clinically relevant increases in calcium-channel blocker levels or effects have been shown for nelfinavir with nifedipine or felodipine, indinavir/ritonavir with amlodipine, diltiazem or nifedipine, and atazanavir with diltiazem. Caution would be required with any of these combinations, anticipating the need to use lower doses of the calcium-channel blocker. The manufacturers specifically recommend that if diltiazem is given with atazanavir the initial dose of diltiazem should be reduced by 50% with subsequent dose titration and ECG monitoring. They also note that verapamil levels may be raised and therefore advise caution. Similarly, the manufaeturers of nifedipine say that blood pressure monitoring is required and a reduction in nifedipine dose may be neeessary if it is given with HIV-protease inhibitors. However, some UK manufacturers (e.g. felodipine, lercanidipine, nimodipine ) recommend avoiding the concurrent use of ritonavir and other protease inhibitors if possible. 

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