Verapamil

Like diltiazem, verapamil belongs to the non-dihydropyridine subclass of calcium channel blockers, which means it acts on both blood vessels and the heart ^{[1, 2]}. However, verapamil has the strongest effect on the heart of all calcium channel blockers.

Verapamil blocks L-type calcium channels in three key locations ^{[1, 3]}:

Heart muscle (myocardium): Reduces the force of heart contractions (negative inotropy). This decreases the heart's oxygen demand and is beneficial in angina ^{[1, 2]}.

Heart's electrical system (SA and AV nodes): These nodes depend on calcium for generating and conducting electrical impulses. By blocking calcium entry, verapamil slows the heart rate (negative chronotropy) and slows conduction through the AV node (negative dromotropy) ^{[1, 3]}. This makes verapamil particularly effective for: - Terminating supraventricular tachycardia (SVT) - Controlling heart rate in atrial fibrillation/flutter

Blood vessel smooth muscle: Causes vasodilation, lowering blood pressure and reducing afterload ^{[1, 2]}.

Verapamil is also used for migraine prevention ^[4]. The mechanism is not fully understood but likely involves modulation of cerebral blood flow, cortical spreading depression, and neurovascular signaling.

Important distinction: Because of its strong cardiac effects, verapamil should generally not be combined with beta-blockers (especially IV) due to the risk of severe bradycardia, heart block, and heart failure ^{[1, 2]}.

When starting verapamil, effects vary by formulation and indication ^{[1, 2]}.

For blood pressure (oral): Blood pressure reduction begins within 1-2 hours (IR) or gradually (ER). Full antihypertensive effect in 1-2 weeks. Extended-release forms are taken once or twice daily.

For SVT (IV): In the hospital, IV verapamil terminates SVT within 1-3 minutes in most patients. This is one of its most dramatic clinical uses.

For angina: Reduction in angina episodes typically begins within 1-2 weeks of starting therapy.

For migraine prevention: As with all preventive migraine treatments, expect 4-8 weeks before seeing a reduction in migraine frequency.

Constipation — the most common complaint [1]: Verapamil causes constipation in 25-40% of patients — significantly more than other calcium channel blockers. This is because it relaxes smooth muscle throughout the GI tract, slowing bowel transit. Start a fiber supplement, drink adequate water, and consider a stool softener when beginning verapamil.

Important: Swallow ER/SR tablets or capsules whole. Do not crush, break, or chew ^[1].

Food — formulation-specific [1, 2]: - Immediate-release: Can be taken with or without food - Calan SR: Take with food to slow absorption and reduce peak-related side effects - Verelan PM: Take at bedtime. Do not take with grapefruit juice - Covera-HS: Take at bedtime on an empty stomach

Grapefruit juice [3, 5]: Grapefruit juice inhibits intestinal CYP3A4, which can increase verapamil levels by 30-50% ^[5]. This may cause excessive blood pressure lowering and bradycardia. Avoid grapefruit juice or limit to very small amounts.

Alcohol [1]: Verapamil inhibits alcohol metabolism, potentially increasing blood alcohol levels by approximately 17% ^[1]. This means you may feel the effects of alcohol more strongly and for longer. Limit alcohol consumption.

High-fiber diet: A high-fiber diet is recommended to manage the constipation caused by verapamil. Include adequate water intake, fruits, vegetables, and consider a fiber supplement.

Hypertension [1, 2]: - IR: Start 80 mg three times daily. Usual range: 240-480 mg/day in 3 divided doses. Maximum: 480 mg/day - Calan SR / Isoptin SR: Start 180 mg once daily (morning). Usual range: 180-480 mg/day in 1-2 divided doses - Verelan (ER capsules): Start 120-240 mg once daily (morning). Maximum: 480 mg/day - Verelan PM: 200 mg at bedtime. Maximum: 400 mg at bedtime - Covera-HS: 180 mg at bedtime. Maximum: 480 mg at bedtime

Angina [1]: - IR: Start 80 mg 3-4 times daily. Usual range: 240-480 mg/day in divided doses - ER formulations: Similar to hypertension dosing

SVT (acute) [1, 6]: - IV: 5-10 mg (0.075-0.15 mg/kg) over 2 minutes. May repeat 10 mg in 15-30 minutes if needed - Contraindicated in patients on beta-blockers (IV) or with pre-excitation (WPW syndrome)

Migraine prevention (off-label) [4]: - Start 80 mg 3 times daily (IR) or 240 mg daily (ER) - Effective dose: 240-480 mg/day

Renal impairment: No dose adjustment needed for mild-moderate impairment. Use with caution in severe impairment ^[1].

Generic verapamil is widely available and affordable ^{[7, 8]}.

Pricing comparison [7, 8]: - Generic verapamil IR: $5-15/month - Generic verapamil ER: $10-30/month - Brand Calan: $100-200/month (rarely prescribed) - Brand Verelan: $200-400/month (rarely prescribed) - IR formulations available on $4 generic programs

Insurance coverage: Generic verapamil is Tier 1 on most formularies ^[8].

Cost-saving tips: - IR tablets are cheapest but require 3x daily dosing - Generic ER formulations offer convenience at moderate cost - GoodRx coupons can reduce prices significantly - Budget for a fiber supplement/stool softener (~$5-10/month) to manage constipation

Pregnancy [1, 2]: Verapamil was formerly classified as FDA Pregnancy Category C. Animal studies have shown some adverse effects at high doses, but human data are limited ^[1].

Verapamil is used during pregnancy for: - Maternal arrhythmias (SVT) - Fetal SVT (treatment via maternal administration — verapamil crosses the placenta) - Hypertension (not first-line; nifedipine, labetalol, and methyldopa preferred)

Verapamil should be used during pregnancy only when the benefit clearly outweighs the risk ^[9].

Breastfeeding [1, 10]: Verapamil is excreted in breast milk, but the estimated infant dose is less than 1% of the maternal dose on a weight-adjusted basis ^[10]. It is generally considered compatible with breastfeeding by most guidelines. Monitor the infant for bradycardia and hypotension.

Generic verapamil has been available for decades ^{[7, 8]}.

Available generic formulations: - Verapamil HCl tablets (IR): 40, 80, 120 mg - Verapamil HCl tablets (SR): 120, 180, 240 mg — equivalent to Calan SR, Isoptin SR - Verapamil HCl capsules (ER): 120, 180, 240, 360 mg — equivalent to Verelan - Verapamil HCl capsules (ER, PM): 100, 200, 300 mg — equivalent to Verelan PM

ER formulations are NOT interchangeable [1, 7]: Different ER products (Calan SR, Verelan, Verelan PM, Covera-HS) have different release profiles and dosing schedules. Switching requires medical supervision.

Brand vs. generic: AB-rated generics for a specific formulation are therapeutically equivalent.