Nifedipine

Your blood vessels have smooth muscle cells that contract when calcium ions flow into them through tiny channels called L-type calcium channels ^{[1, 2]}. When these muscles contract, the blood vessels narrow and blood pressure rises. In the coronary arteries (which supply blood to the heart), this narrowing can reduce blood flow and cause angina (chest pain).

Nifedipine works by blocking L-type calcium channels primarily in vascular smooth muscle ^{[1, 3]}. This prevents calcium from entering the cells, causing the muscles to relax. As a result:

- Peripheral arteries dilate — reducing peripheral vascular resistance and lowering blood pressure ^{[1, 2]} - Coronary arteries dilate — increasing blood flow to the heart muscle and relieving angina ^{[1, 3]} - Reduced cardiac workload — by lowering afterload (the resistance the heart pumps against), the heart does not have to work as hard

Unlike diltiazem and verapamil (non-dihydropyridine calcium channel blockers), nifedipine has minimal direct effect on the heart's electrical system or contractility ^{[2, 4]}. It primarily acts on blood vessels. However, the rapid blood pressure drop from immediate-release nifedipine can trigger reflex tachycardia (the heart speeds up to compensate for the sudden pressure drop), which is why extended-release formulations are strongly preferred ^{[3, 5]}.

Nifedipine is also used off-label in obstetrics as a tocolytic agent to delay preterm labor by relaxing uterine smooth muscle ^[6].

With extended-release nifedipine (the recommended formulation) ^{[1, 2]}:

First few days: You may experience headache, flushing, and mild dizziness as your blood vessels dilate. These effects are usually mild and improve over the first 1-2 weeks.

First 1-2 weeks: Blood pressure begins to decrease gradually. Ankle swelling (peripheral edema) may develop — this is caused by vasodilation, not heart failure. It occurs more frequently at higher doses.

2-4 weeks: Full antihypertensive effect is typically achieved. Angina episodes should decrease in frequency.

Important notes: - Swallow ER tablets whole — do not crush, break, or chew ^[1]. The tablet uses an osmotic pump system (GITS). You may see an empty tablet shell in your stool — this is normal and does not mean the medication was not absorbed. - Take at the same time each day, usually in the morning - Report rapidly worsening ankle swelling, chest pain, or heart pounding to your doctor

Avoid immediate-release nifedipine for hypertension [5]: Sublingual or chewed IR nifedipine for hypertensive emergencies has been associated with strokes and heart attacks and is strongly discouraged.

Grapefruit — IMPORTANT [1, 3, 5]: Grapefruit and grapefruit juice are significant interactors with nifedipine. Grapefruit inhibits intestinal CYP3A4 enzymes, which can increase nifedipine blood levels by 50-100% ^{[3, 5]}. This can cause excessive blood pressure lowering, headache, flushing, and dizziness. Avoid grapefruit or limit to very small amounts and discuss with your pharmacist.

Food — formulation-specific [1]: - Procardia XL (GITS): Can be taken with or without food. Food does not significantly affect drug absorption from the osmotic pump system. - Adalat CC: Should be taken on an empty stomach — a high-fat meal can increase peak levels by 50-60%, potentially increasing side effects. - Immediate-release: Absorption is not significantly affected by food.

Alcohol [1]: Alcohol enhances the vasodilatory effects of nifedipine, potentially causing excessive blood pressure lowering, dizziness, and flushing. Limit alcohol intake, especially during the first few weeks of treatment.

Hypertension [1, 2]: - Procardia XL (GITS): Start 30 or 60 mg once daily. May increase at 7-14 day intervals. Maximum: 120 mg/day - Adalat CC: Start 30 mg once daily. May increase at 7-14 day intervals. Maximum: 90 mg/day - Immediate-release: Not recommended for hypertension due to safety concerns ^[5]

Chronic stable angina [1, 4]: - Extended-release: Start 30 or 60 mg once daily. Titrate over 7-14 days. Maximum: 120 mg/day - Immediate-release (less preferred): Start 10 mg three times daily. Usual range: 10-20 mg three times daily. Maximum: 180 mg/day

Preterm labor (off-label) [6]: - Loading dose: 30 mg orally, then 10-20 mg every 4-6 hours for 48 hours - Maintenance: 10-20 mg every 6-8 hours - Used as a tocolytic in selected patients

Raynaud phenomenon (off-label) [7]: - Extended-release: 30-60 mg once daily

Elderly patients: Start at the lower end of the dosing range. Nifedipine clearance is reduced in the elderly ^[1].

Generic nifedipine ER has been available for many years and is moderately priced ^{[8, 9]}.

Pricing comparison [8, 9]: - Generic nifedipine ER: $15-40/month - Brand Procardia XL: $200-400/month (rarely prescribed) - Brand Adalat CC: $150-300/month (rarely prescribed) - Savings: approximately 85-90% with generic

Insurance coverage: Generic nifedipine ER is on most formularies as Tier 1 or Tier 2 ^[9].

Cost-saving tips: - Available on many $4/$10 generic programs at major pharmacies - GoodRx coupons can reduce prices to $10-20/month - Some ER formulations may be less expensive than others — ask your pharmacist - Patient assistance programs available from Bayer (Adalat CC) if needed

Pregnancy [1, 6]: Nifedipine is one of the most commonly used antihypertensives in pregnancy and has a relatively favorable safety profile. It was formerly classified as FDA Pregnancy Category C.

Nifedipine is widely used for: - Chronic hypertension in pregnancy ^[4] - Acute severe hypertension (as an alternative to IV labetalol or hydralazine) - Tocolysis — to delay preterm labor by relaxing uterine smooth muscle ^[6]

Extensive clinical experience suggests that nifedipine does not increase the risk of birth defects when used in the second and third trimesters. First-trimester data are more limited. It is recommended by ACOG and other guidelines as a first-line antihypertensive in pregnancy ^{[4, 6]}.

Breastfeeding [1, 10]: Nifedipine is excreted in breast milk in small amounts. The estimated infant dose is less than 5% of the maternal dose on a weight-adjusted basis. The American Academy of Pediatrics considers nifedipine compatible with breastfeeding ^[10]. It is one of the preferred calcium channel blockers during lactation.

Generic nifedipine ER has been available for many years ^{[8, 9]}.

Available generic formulations: - Nifedipine ER tablets (GITS osmotic pump type): 30, 60, 90 mg — equivalent to Procardia XL - Nifedipine ER tablets (coat-core type): 30, 60, 90 mg — equivalent to Adalat CC - Nifedipine IR capsules: 10, 20 mg — equivalent to Procardia (rarely used)

Important: Procardia XL generics and Adalat CC generics are not interchangeable with each other because they use different release technologies ^[8]. Switching between GITS-type and coat-core-type ER tablets should be done under medical supervision.

Generic vs. brand: No clinically meaningful differences in efficacy or safety between AB-rated generic and brand products.