Lack of Effects of Diltiazem on Digoxin Pharmacokinetics

Diltiazem is a member of a class of pharmacologic agents that block the passage of calcium ions across cell membranes, the calcium‐channel blockers. Several investigators have reported a clinically important pharmacokinetic and pharmacologic interaction between digoxin and verapamil.1–4 Despite earlier suggestions of such an interaction with nifedipine, recent works have convincingly shown that no pharmacokinetic changes occur.5–7 Thus, it appears that nifedipine has no clinically significant interaction with digoxin. Similar work has been limited with diltiazem. A recent investigation by Yoshida and associates,8 suggested no increase in digoxin serum concentration and a slight decrease in renal digoxin clearance after diltiazem had been added versus a control period. Rameis and co‐workers9 recently reported a 22.4% increase in serum digoxin concentration when diltiazem was added. The purpose of this study was to further evaluate this potential interaction.