Pharmacokinetics of diltiazem in patients undergoing coronary artery bypass grafting

The pharmacokinetics of oral diltiazem (DZ) were studied in 10 patients on the day before cardiac surgery and on the next day during surgery and cardiopulmonary bypass (CPB). Six patients were taking DZ 60 mg q.i.d. and four patients were taking DZ 90 mg q.i.d. All had been receiving DZ treatment for at least 3 months. The plasma concentration profile of DZ on the day before surgery was assumed to reflect the steady-state condition. DZ showed dose-dependent kinetics. On the day of surgery, the levels of total DZ (TDZ) at 15 min and 1 h after the initiation of CPB were significantly reduced (approximately 50%) when compared with the pre-CPB level. The levels of unbound DZ (FDZ) and the two major metabolites, N-demethyl DZ (MA) and deacetyl-DZ (M1) were not changed significantly by CPB. The plasma unbound fraction value increased sharply from 0.43 +/- 0.12 before the onset of CPB to a peak value of 0.83 +/- 0.12 during CPB, and returned to baseline level 24 h after dosing. We conclude that CPB decreases the TDZ concentration but has little effect on FDZ, MA, and M1 levels. The lack of effect of CPB on FDZ was related to the reduction of plasma protein binding of DZ.