Pharmacokinetics of verapamil in patients with hypertension

Summary Twelve hypertensive patients (WHO Stage I-II) were given oral verapamil (Isoptin) b.d. or t.d.s. as long-term treatment. The pharmacokinetics of verapamil and norverapamil were studied both after single and b.d. and t.d.s. doses of verapamil 240, 360 or 480 mg daily adjusted according to the blood pressure response. The apparent oral clearance of verapamil was decreased after both the twice and thrice daily dosage regimens (1.38 and 1.841/min, respectively) as compared to the single dose (4.39 l/min). The plasma half-life of verapamil was increased from 3.34 h (single dose) to 4.65 h (b.i.d.). Decreased elimination of norverapamil was also found after multiple doses of verapamil, as shown by an increase in the adjusted AUC of norverapamil (adjusted to a verapamil dose of 80 mg), namely from 574.9 h·ng·ml^–1 (single dose) to 1172 h·ng·ml^–1 (b.d.) and to 841 h·ng·ml^–1 (t.d.s.). The plasma half-life of norverapamil increase from 5.68 h to 7.34 h during twice daily dosing. During thrice daily verapamil, no increase in plasma half-life was found either for verapamil or norverapamil, probably due to the relatively short sampling time (6 h). The plasma concentration of verapamil and the reduction in supine systolic and diastolic blood pressure were correlated. The mean decrease in supine systolic blood pressure was 5.8 mm Hg per 100 ng verapamil/ml plasma, and for diastolic pressure 2.9 mm Hg per 100 ng verapamil/ml plasma. The mean steadystate plasma concentrations of verapamil were similar after twice and thrice daily dosing regimens, which agrees with the clinical observation that blood pressure control in hypertensive patients is as good after verapamil b.d. and t.d.s.