Diltiazem

Your heart and blood vessels depend on calcium ions flowing into muscle cells to contract ^{[1, 2]}. When calcium enters the smooth muscle cells of blood vessel walls, the vessels constrict and blood pressure rises. When calcium enters heart muscle cells, the heart contracts more forcefully and conducts electrical signals faster.

Diltiazem blocks L-type calcium channels in both the heart and blood vessels ^{[1, 3]}. This produces two important effects:

On blood vessels: By reducing calcium entry into vascular smooth muscle, diltiazem causes blood vessels to relax and widen (vasodilation). This lowers blood pressure and reduces the workload on the heart, which also helps relieve angina (chest pain caused by reduced blood flow to the heart) ^{[1, 2]}.

On the heart: Unlike dihydropyridine calcium channel blockers (like amlodipine and nifedipine), diltiazem also acts directly on the heart. It slows the heart rate, reduces the force of heart contractions, and slows electrical conduction through the AV node ^{[1, 3]}. This makes diltiazem particularly useful for controlling heart rate in atrial fibrillation and for treating certain types of rapid heart rhythms.

This dual action on both blood vessels and the heart distinguishes diltiazem from other calcium channel blockers and makes it versatile for multiple cardiovascular conditions ^{[2, 4]}.

When starting diltiazem, effects depend on the condition being treated and the formulation ^{[1, 2]}.

For blood pressure: You may notice a gradual reduction over the first 1-2 weeks. Extended-release formulations are taken once daily, making adherence easier. The full antihypertensive effect is typically seen within 2-4 weeks.

For angina: Relief from chest pain episodes may begin within the first week. You may notice fewer episodes and increased exercise tolerance.

For heart rate control (atrial fibrillation): If given intravenously in the hospital, heart rate slowing occurs within 2-7 minutes. Oral diltiazem controls heart rate over several days.

Common early experiences: Mild headache, dizziness, and swelling in the ankles or feet are the most common initial side effects. These often improve after the first few weeks. Constipation may occur and can be managed with dietary fiber and adequate fluids.

Important: Do not crush, chew, or break extended-release tablets or capsules. Swallow them whole ^[1]. Grapefruit juice can increase diltiazem levels — discuss with your pharmacist.

Food interactions [1, 2]: - Immediate-release diltiazem: Can be taken with or without food - Extended-release formulations: Follow specific product instructions — some should be taken on an empty stomach, others with food. Cardizem CD and Tiazac can be taken without regard to meals ^[1] - Do not crush, chew, or break extended-release capsules or tablets

Grapefruit juice [3, 5]: Grapefruit and grapefruit juice inhibit CYP3A4 in the intestine, which can increase diltiazem levels by 20-40%. This may lead to excessive blood pressure lowering and slow heart rate. Avoid grapefruit or limit intake to small amounts while on diltiazem.

Alcohol [1]: Alcohol can enhance the blood pressure-lowering and heart rate-slowing effects of diltiazem. Limit alcohol consumption to moderate amounts and be aware of increased dizziness or lightheadedness.

High-fat meals: A high-fat meal may delay the absorption of some extended-release formulations but generally does not affect total drug exposure ^[1].

Hypertension [1, 2]: - Extended-release (Cardizem CD, Tiazac): Start 180-240 mg once daily. May increase at 1-2 week intervals. Usual range: 180-480 mg/day. Maximum: 480 mg/day - Extended-release (Cardizem LA): Start 180-240 mg once daily. Maximum: 540 mg/day - Immediate-release: 30 mg four times daily initially (less commonly used for hypertension)

Angina (chronic stable) [1, 4]: - Immediate-release: Start 30 mg four times daily. Increase gradually at 1-2 day intervals. Usual dose: 180-360 mg/day in divided doses - Extended-release: 120-180 mg once daily, titrate as needed

Atrial fibrillation/flutter (rate control) [1, 6]: - Immediate-release: 120-360 mg/day in 3-4 divided doses - Extended-release: 120-360 mg once daily, titrate to target heart rate - IV: 0.25 mg/kg bolus over 2 min (hospital setting), may repeat at 0.35 mg/kg

CRITICAL — formulation non-interchangeability [1]: Extended-release products (Cardizem CD, Cardizem LA, Tiazac, Dilacor XR) are NOT interchangeable on a mg-per-mg basis. Each has different pharmacokinetic profiles.

Generic diltiazem is widely available and has been off-patent for many years ^{[7, 8]}.

Pricing comparison [7, 8]: - Generic diltiazem ER (CD formulation): $10-30/month - Generic diltiazem IR: $8-20/month - Brand Cardizem CD: $200-400/month - Brand Tiazac: $150-300/month - Savings: approximately 85-95% with generic

Insurance coverage: Generic diltiazem is Tier 1 on most formularies. Extended-release formulations may be Tier 2 depending on the specific product ^[8].

Cost-saving tips: - Generic ER capsules are available at most $4/$10 programs at major pharmacies - GoodRx coupons can reduce prices further - If brand is needed, manufacturer coupons may be available - Ask your pharmacist which generic ER formulation is least expensive — prices vary between CD, LA, and other ER versions

Pregnancy [1, 2]: Diltiazem was formerly classified as FDA Pregnancy Category C. Animal studies have shown adverse effects on embryonic/fetal development (skeletal abnormalities) at doses 5-10 times the human dose ^[1].

There are no adequate and well-controlled studies in pregnant women. Diltiazem should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. For hypertension in pregnancy, preferred alternatives include labetalol, methyldopa, and nifedipine (which has more safety data in pregnancy than diltiazem) ^[4].

Breastfeeding [1, 9]: Diltiazem is excreted in human breast milk. In one report, diltiazem levels in breast milk were approximately equal to serum levels ^[1]. The American Academy of Pediatrics has considered diltiazem compatible with breastfeeding in limited data, but monitoring the infant for bradycardia and hypotension is recommended. Discuss risks and benefits with your doctor.

Generic diltiazem has been available for decades and is dramatically less expensive than brand products ^{[7, 8]}.

Available generic formulations: - Immediate-release tablets: 30, 60, 90, 120 mg - Extended-release capsules (CD type): 120, 180, 240, 300, 360 mg - Extended-release tablets (LA type): 120, 180, 240, 300, 360, 420 mg - Extended-release capsules (other): Various strengths

IMPORTANT — ER formulations are NOT interchangeable [1, 7]: Different extended-release products have different release profiles. Switching between brands (e.g., Cardizem CD to Tiazac) should be done under physician supervision with blood pressure monitoring, even though both are ER formulations.

Generic substitution: AB-rated generics for a specific formulation are interchangeable. However, not all ER products are AB-rated to each other.