Pharmacokinetics of calcium channel blocking agents

Sustained-release and instant-release verapamil in treatment of angina pectoris

The efficacy of a sustained-release preparation of verapamil (verapamil-SR) has been compared with that of a conventional instant-release formulation (verapamil-IR) in 10 patients with stable angina pectoris treated for 3 weeks with both preparations. The diurnal serum concentrations of verapamil and norverapamil did not differ significantly during treatment with verapamil-IR 120 mg t.i.d. and verapamil-SR 360 mg once daily, but verapamil-SR 240 mg produced significantly lower serum concentrations. The differences did not affect the exercise capacity or the occurrence of ST-segment depression during maximal exercise. Verapamil-SR was well tolerated. A multiple instant-release dosage regime can now be replaced by once daily administration of the sustained-release preparation.

Pharmacokinetics of verapamil in patients with hypertension

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 (4.391/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 X ng X ml-1 (single dose) to 1172 h X ng X ml-1 (b.d.) and to 841 h X ng X 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.(ABSTRACT TRUNCATED AT 250 WORDS)