VERAPAMIL HYDROCHLORIDE — verapamil hydrochloride tablet, extended release
State of Florida DOH Central Pharmacy
Verapamil hydrochloride is a calcium ion influx inhibitor (slow-channel blocker or calcium ion antagonist). The tablets are designed for extended-release of the drug in the gastrointestinal tract, extended-release characteristics are not altered when the tablet is divided in half.
The structural formula of verapamil hydrochloride is given below:
C27 H38 N2 O4 •HCl M.W.491.06
The chemical name is: Benzeneacetronitrile, α[3-[[2-(3,4-dimethoxyphenyl) ethyl]methylamino] propyl]-3,4-dimethoxy-α-(1-methylethyl) hydrochloride
Verapamil hydrochloride is an almost white, crystalline powder, practically free of odor, with a bitter taste. It is soluble in water, chloroform, and methanol. Verapamil hydrochloride is not chemically related to other cardioactive drugs.
Each film-coated extended-release tablet for oral administration contains 120 mg, 180 mg, or 240 mg of verapamil hydrochloride, USP. Each tablet contains the following inactive ingredients: carnauba wax, D&C yellow #10 aluminum lake, hypromellose, iron oxide yellow, magnesium stearate, microcrystalline cellulose, polydextrose, polyethylene glycol 8000, povidone, sodium alginate, titanium dioxide and triacetin.
Verapamil hydrochloride is a calcium ion influx inhibitor (slow-channel blocker or calcium ion antagonist) that exerts its pharmacologic effects by modulating the influx of ionic calcium across the cell membrane of the arterial smooth muscle as well as in conductile and contractile myocardial cells.
Verapamil exerts antihypertensive effects by decreasing systemic vascular resistance, usually without orthostatic decreases in blood pressure or reflex tachycardia; bradycardia (rate less than 50 beats/min) is uncommon (1.4%). During isometric or dynamic exercise, verapamil does not alter systolic cardiac function in patients with normal ventricular function.
Verapamil does not alter total serum calcium levels. However, one report suggested that calcium levels above the normal range may alter the therapeutic effect of verapamil.
Other Pharmacologic Actions of Verapamil Hydrochloride Include the Following:
Verapamil dilates the main coronary arteries and coronary arterioles, both in normal and ischemic regions, and is a potent inhibitor of coronary artery spasm, whether spontaneous or ergonovine-induced. This property increases myocardial oxygen delivery in patients with coronary artery spasm and is responsible for the effectiveness of verapamil in vasospastic (Prinzmetal’s or variant) as well as unstable angina at rest. Whether this effect plays any role in classical effort angina is not clear, but studies of exercise tolerance have not shown an increase in the maximum exercise rate-pressure product, a widely accepted measure of oxygen utilization. This suggests that, in general, relief of spasm or dilation of coronary arteries is not an important factor in classical angina.
Verapamil regularly reduces the total systemic resistance (afterload) against which the heart works both at rest and at a given level of exercise by dilating peripheral arterioles.
Electrical activity through the AV node depends, to a significant degree, upon calcium influx through the slow channel. By decreasing the influx of calcium, verapamil prolongs the effective refractory period within the AV node and slows AV conduction in a rate-related manner.
Normal sinus rhythm is usually not affected, but in patients with sick sinus syndrome, verapamil may interfere with sinus-node impulse generation and may induce sinus arrest or sinoatrial block. Atrioventricular block can occur in patients without preexisting conduction defects (see WARNINGS).
Verapamil does not alter the normal atrial action potential or intraventricular conduction time, but depresses amplitude, velocity of depolarization, and conduction in depressed atrial fibers. Verapamil may shorten the antegrade effective refractory period of the accessory bypass tract. Acceleration of ventricular rate and/or ventricular fibrillation has been reported in patients with atrial flutter or atrial fibrillation and a coexisting accessory AV pathway following administration of verapamil (see WARNINGS).
Verapamil has a local anesthetic action that is 1.6 times that of procaine on an equimolar basis. It is not known whether this action is important at the doses used in man.
With the immediate-release formulation, more than 90% of the orally administered dose of verapamil hydrochloride is absorbed. Because of rapid biotransformation of verapamil during its first pass through the portal circulation, bioavailability ranges from 20% to 35%. Peak plasma concentrations are reached between 1 and 2 hours after oral administration. Chronic oral administration of 120 mg of verapamil hydrochloride every 6 hours resulted in plasma levels of verapamil ranging from 125 to 400 ng/mL, with higher values reported occasionally. A nonlinear correlation between the verapamil dose administered and verapamil plasma level does exist. In early dose titration with verapamil, a relationship exists between verapamil plasma concentration and prolongation of the PR interval. However, during chronic administration this relationship may disappear. The mean elimination half-life in single-dose studies ranged from 2.8 to 7.4 hours. In these same studies, after repetitive dosing, the half-life increased to a range from 4.5 to 12.0 hours (after less than 10 consecutive doses given 6 hours apart). Half-life of verapamil may increase during titration. No relationship has been established between the plasma concentration of verapamil and a reduction in blood pressure.
Aging may affect the pharmacokinetics of verapamil. Elimination half-life may be prolonged in the elderly. In multiple-dose studies under fasting conditions, the bioavailability, measured by AUC, of verapamil hydrochloride extended-release tablets was similar to verapamil hydrochloride immediate-release tablets; rates of absorption were of course different.
In a randomized, single-dose, crossover study using healthy volunteers, administration of 240 mg verapamil hydrochloride extended-release tablets with food produced peak plasma verapamil concentrations of 79 ng/mL; time to peak plasma verapamil concentration of 7.71 hours; and AUC (0-24 hr) of 841 ng . hr/mL. When verapamil hydrochloride extended-release tablets were administered to fasting subjects, peak plasma verapamil concentration was 164 ng/mL; time to peak plasma verapamil concentration was 5.21 hours; and AUC (0-24 hr) was 1,478 ng . hr/mL. Similar results were demonstrated for plasma norverapamil. Food thus produces decreased bioavailability (AUC) but a narrower peak-to-trough ratio. Good correlation of dose and response is not available, but controlled studies of verapamil hydrochloride extended-release tablets have shown effectiveness of doses similar to the effective doses of verapamil hydrochloride immediate-release tablets.
In healthy men, orally administered verapamil hydrochloride undergoes extensive metabolism in the liver. Twelve metabolites have been identified in plasma; all except norverapamil are present in trace amounts only. Norverapamil can reach steady-state plasma concentrations approximately equal to those of verapamil itself. The cardiovascular activity of norverapamil appears to be approximately 20% that of verapamil. Approximately 70% of an administered dose is excreted as metabolites in the urine and 16% or more in the feces within 5 days. About 3% to 4% is excreted in the urine as unchanged drug. Approximately 90% is bound to plasma proteins. In patients with hepatic insufficiency, metabolism of immediate-release verapamil is delayed and elimination half-life prolonged up to 14 to 16 hours (see PRECAUTIONS); the volume of distribution is increased and plasma clearance reduced to about 30% of normal. Verapamil clearance values suggest that patients with liver dysfunction may attain therapeutic verapamil plasma concentrations with one third of the oral daily dose required for patients with normal liver function.
After four weeks of oral dosing (120 mg q.i.d.), verapamil and norverapamil levels were noted in the cerebrospinal fluid with estimated partition coefficient of 0.06 for verapamil and 0.04 for norverapamil.
In ten healthy males, administration of oral verapamil (80 mg every 8 hours for 6 days) and a single oral dose of ethanol (0.8 g/kg) resulted in a 17% increase in mean peak ethanol concentrations (106.45 ± 21.40 to 124.23 ± 24.74 mg•hr/dL) compared to placebo. The area under the blood ethanol concentration versus time curve (AUC over 12 hours) increased by 30% (365.67 ± 93.52 to 475.07 ± 97.24 mg•hr/dL). Verapamil AUCs were positively correlated (r = 0.71) to increased ethanol blood AUC values (see PRECAUTIONS , Drug Interactions).
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