Diltiazem retards the metabolism of oral prednisone with effects on T‐cell markers

Abstract

Abstract: The area under the time–plasma concentration curve (AUC) was measured for prednisolone (the major active metabolite of prednisone) after ingestion of 15 mg of prednisone (phase 1) and again after 3 d of oral diltiazem (180 mg/d) followed by the same dose of oral prednisone (phase 2) in eight normal adult patients. Diltiazem increased the prednisolone AUC by 21% (range 3–38%), from 1297 ± 157 ng/h/mL to 1560 ± 169 ng/h/mL (p=0.001). This effect was associated with a greater decrease from baseline in CD3+ lymphocyte number at 4 h after prednisone ingestion (596 ± 175 vs. 516 ± 140, p=0.05), a larger percentage decrease of circulating CD3+ lymphocytes at 8 h (43 ± 19% vs. 53 ± 19%, p=0.04), and a decrease in the number of CD3+ CD8+ T cells at 4 h post‐prednisone ingestion (279 ± 81 vs. 236 ± 51, p=0.04). Diltiazem retards prednisolone metabolism and when used chronically with prednisone could conceivably, in some patients, enhance its immunologic and other clinical effects. Potentiation of prednisone side‐effects by diltiazem may be of special interest in pediatric patients, and possible diltiazem–prednisone interactions merit study in this population.