Absence of a dose-response of cyclosporine levels to clinically used doses of diltiazem and verapamil.
We examined the effect of different doses of calcium channel blockers on plasma cyclosporine levels. As previously reported by multiple investigators, we observed that the administration of verapamil or diltiazem, but not nifedipine or isradipine, caused a significant increase in plasma cyclosporine levels achieved for a given dose of cyclosporine. In this article, we show that the effect of verapamil and diltiazem on cyclosporine levels appears to be independent of dosage within their usual prescription range.