Overview
DESCRIPTION Verapamil hydrochloride is a calcium ion influx inhibitor (slow-channel blocker or calcium ion antagonist) available for oral administration in film-coated tablets containing 40 mg, 80 mg, or 120 mg of verapamil hydrochloride. The structural formula of verapamil hydrochloride is: Benzeneacetonitrile,...
Mechanism of Action
CLINICAL PHARMACOLOGY 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. Mechanism of action Angina: The precise mechanism of action of verapamil hydrochloride as an antianginal agent remains to be fully determined, but includes the following two mechanisms: 1 . Relaxation and prevention of coronary artery spasm: 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.
Indications
- INDICATIONS AND USAGE Verapamil Hydrochloride Tablets are indicated for the treatment of the following: Angina 1. Angina at rest including: – Vasospastic (Prinzmetal’s variant) angina – Unstable (crescendo, pre-infarction) angina 2. Chronic stable angina (classic effort-associated angina) Arrhythmias 1. In association with digitalis for the control of ventricular rate at rest and during stress in patients with chronic atrial flutter and/or atrial fibrillation (see WARNINGS; Accessory bypass tract ) 2.
Common Doses
- 480 mg
- 80 mg
- 120 mg
- 40 mg
Dosage
DOSAGE AND ADMINISTRATION The dose of verapamil must be individualized by titration. The usefulness and safety of dosages exceeding 480 mg/day have not been established; therefore, this daily dosage should not be exceeded. Since the half-life of verapamil increases during chronic dosing, maximum response may be delayed. Angina: Clinical trials show that the usual dose is 80 mg to 120 mg three times a day. However, 40 mg three times a day may be warranted in patients who may have an increased response to verapamil (e.g., decreased hepatic function, elderly, etc.).
Contraindications
- CONTRAINDICATIONS Verapamil Hydrochloride Tablets are contraindicated in: 1. Severe left ventricular dysfunction (see WARNINGS ) 2. Hypotension (systolic pressure less than 90 mm Hg) or cardiogenic shock 3. Sick sinus syndrome (except in patients with a functioning artificial ventricular pacemaker) 4. Second-or-third-degree AV block (except in patients with a functioning artificial ventricular pacemaker) 5. Patients with atrial flutter or atrial fibrillation and an accessory bypass tract (e.g., Wolff-Parkinson-White, Lown-Ganong-Levine syndromes) (see WARNINGS ) 6.
Side Effects
- ADVERSE REACTIONS Serious adverse reactions are uncommon when verapamil hydrochloride therapy is initiated with upward dose titration within the recommended single and total daily dose. See WARNINGS for discussion of heart failure, hypotension, elevated liver enzymes, AV block, and rapid ventricular response. Reversible (upon discontinuation of verapamil) non-obstructive, paralytic ileus has been infrequently reported in association with the use of verapamil.
Interactions
- Drug interactions Cytochrome inducers/inhibitors: In vitro metabolic studies indicate that verapamil is metabolized by cytochrome P450 CYP3A4, CYP1A2, CYP2C8, CYP2C9, and CYP2C18. Clinically significant interactions have been reported with inhibitors of CYP3A4 (e.g., erythromycin, ritonavir) causing elevation of plasma levels of verapamil while inducers of CYP3A4 (e.g., rifampin) have caused a lowering of plasma levels of verapamil.