Clinical relevance of verapamil plasma levels in stable angina pectoris

Pharmacokinetics of sustained-release verapamil after a single administration and at steady state

Pharmacokinetics of conventional 80 mg tablets and two types of sustained-release (SR) tablets containing 120 and 200 mg of verapamil were compared cross-over in 12 healthy volunteers. Serum concentrations of verapamil and norverapamil were analyzed both after a single oral dose and at steady state after t.i.d. administration of conventional tablets and b.i.d. administration of SR tablets. After 120 mg SR tablets serum concentrations of verapamil usually remained below 100 ng/ml for 5 days. This inadequate bioavailability was caused by very slow absorption. The relative bioavailability of verapamil in 200 mg SR tablets was 93-96% as compared to the conventional tablets. After 200 mg X 2 and 80 mg X 3, the peak serum levels were about 300 and 190 ng/ml, respectively and the trough levels 123-153 and 52-56 ng/ml, respectively. The verapamil/norverapamil ratio varied from 0.69 to 0.84 after a single dose and from 0.8 to 0.93 at steady-state. By the 4th days of treatment, the accumulation ratios ranged between 1.75-2.07 and 1.30-1.75 for verapamil and norverapamil, respectively. For each preparation studied, the apparent Cltot of verapamil was significantly reduced at steady-state. These results show that 200 mg SR verapamil tablets fulfill the basic requirements of retard preparations allowing for twice or even once daily administration.

Plasma levels and myocardial content of verapamil, norverapamil and two N-dealkyl-metabolites in man

The plasma levels and myocardial content of verapamil and its metabolites norverapamil, N-dealkylverapamil and N-dealkylnorverapamil were determined in 15 patients with valvular [3] or ischaemic [12] heart disease. The mean myocardial plasma concentration ratio (M/P) was 7.05 for verapamil, 11.45 for norverapamil, 8.93 for N-dealkylverapamil, and 11.33 for N-dealkylnorverapamil, with great interpatient variability. The highest M/P ratios of verapamil were generally found in patients with the lowest plasma levels, suggesting that saturable tissue uptake may occur.

Use of oral verapamil in long-term treatment of neonatal, paroxysmal supraventricular tachycardia. A pharmacokinetic study

Efficacy and pharmacokinetics of verapamil were studied in two neonates affected by supraventricular paroxysmal tachycardia, under maintenance treatment with the drug. Verapamil proved to be fully effective in suppressing arrhythmic episodes at the daily doses of 1.5 mg/kg four times a day in case 1 and of 2 mg/kg in case 2. The results of plasma half-life of the drug, calculated in a dose interval, were 3.14 hr and 2.10 hr, respectively. In patient 2, doses less than 0.95 mg/kg four times a day did not produce detectable drug plasma levels, while a further stepwise increase of dose up to 2 mg/kg four times a day produced a steep rise in trough concentration. So, in view of this dose-concentration relationship, caution is recommended in adjusting verapamil oral dosage.

Calcium channel blockers in emergency medicine

Diltiazem, nifedipine, and verapamil inhibit calcium entry into cells via different mechanisms with different pharmacologies. They display different relative effects on different cardiovascular functions, a complex interplay of direct actions and adrenergic reflexes. Peripheral arterial vasorelaxation causes adrenergic reflex activity which opposes their direct negative chronotropic, dromotropic, inotropic, and hypotensive actions. Verapamil's most potent activity is electrophysiologic, and nifedipine's effects are hemodynamic; diltiazem acts like a less-potent combination of verapamil and nifedipine. All three drugs are efficacious in angina. These three drugs may not be interchangeable in all patients, but individualization of therapy is possible. Future indications for calcium channel blocker therapy may include hypertrophic cardiomyopathy, cerebral vasospasm, migraine headaches, pulmonary hypertension, asthma, esophageal spasm, intestinal ischemia, Raynaud's phenomenon, dysmenorrhea, and premature labor.

Reversal of adriamycin resistance by verapamil in human ovarian cancer

The effectiveness of adriamycin in the treatment of ovarian cancer and other human tumors has been limited by the development of drug resistance. Verapamil, a calcium channel blocking agent, completely reversed adriamycin resistance in human ovarian cancer cells with moderate (three- to sixfold) degrees of resistance and partially reversed resistance in highly (150-fold) resistant cells. The potentiating effect of verapamil was due to inhibition of adriamycin efflux in the resistant cells. These results have led to a clinical trial of adriamycin and verapamil in refractory ovarian cancer patients.

Clinical pharmacokinetics of verapamil

Verapamil is widely used in the treatment of supraventricular tachyarrhythmias as well as for hypertension and control of symptoms in angina pectoris. Unlike other calcium antagonists, detailed pharmacokinetic data are available for verapamil. Plasma concentrations of verapamil appear to correlate with both electrophysiological and haemodynamic activity after either intravenous or oral drug administration, although considerable intra- and intersubject variation has been found in the intensity of pharmacological effects resulting at specific plasma drug levels. Verapamil is widely distributed throughout body tissues; animal studies suggest that drug distribution to target organs and tissues is different with parenteral administration from that found after oral administration. The drug is eliminated by hepatic metabolism, with excretion of inactive products in the urine and/or faeces. An N-demethylated metabolite, norverapamil, has been shown to have a fraction of the vasodilator effect of the parent compound in in vitro studies. After intravenous administration, the systemic clearance of verapamil appears to approach liver blood flow. The high hepatic extraction results in low systemic bioavailability (20%) after oral drug administration. Multicompartmental kinetics are observed after single doses; accumulation occurs during multiple-dose oral administration with an associated decrease in apparent oral clearance. Norverapamil plasma concentrations approximate those of verapamil following single or multiple oral doses of the parent drug. Because of the complex pharmacokinetics associated with multiple-dose administration and the variation in individual patient responsiveness to the drug, 'standard' dosing recommendations are difficult to determine; use of verapamil must be titrated to a clinical end-point. Further, the potential for alteration in verapamil's disposition by the presence of hepatic dysfunction or cardiovascular disorders which result in altered hepatic blood flow is only now becoming apparent. A potentially toxic interaction has been reported between verapamil and digoxin, in which renal excretion of the glycoside is impaired, but the true clinical significance of this remains debatable. Combination therapy with verapamil and beta-adrenoceptor blocking compounds has been advocated by some investigators, but may be hazardous because of the additive negative inotropic and chronotropic effects inherent in both agents.

A simple sensitive radioreceptor assay for calcium antagonist drugs

A radioreceptor assay for calcium channel antagonist drugs described here is based on the ability of these drugs to affect 3H-nitrendipine binding to calcium channels. All the known calcium channel antagonists may be assayed in this manner. The assay can detect 10-100 nM (4 - 40 ng/ml) nimodipine, 10-100 nM (3.5 - 35 ng/ml) nifedipine, 3-30 microM (1.2 - 12 micrograms/ml) prenylamine, 0.1 - 1.0 microM (49 - 490 ng/ml) verapamil and 3-30 microM (1.2 - 12 micrograms/ml) diltiazem. These values cover the range of concentrations of calcium channel antagonists that are clinically important. As the radioreceptor assay detects active metabolites as well as the parent drugs, it should prove a useful adjunct in cardiovascular therapy. The method is more reproducible, simpler and less expensive than other methods such as high pressure liquid chromatography.