nifedipine
Adalat, Adalat CC, Procardia, Procardia XL

Available forms
Available by prescription only
Capsules: 10 mg, 20 mg
Tablets (extended-release): 30 mg, 60 mg, 90 mg

Indications and dosages
 Management of Prinzmetal’s (variant) angina or chronic stable angina. Adults: Starting dose is 10 mg P.O. t.i.d. Usual effective dosage range is 10 to 20 mg t.i.d. Some patients may need up to 30 mg q.i.d. Or, 30 to 60 mg (extended-release) P.O. daily. Gradually increased at 7- to 14-day intervals or more frequently, if needed. Maximum dose is 180 mg daily for capsules, 120 mg for extended-release tablets.
 Hypertension. Adults: Initially, 30 to 60 mg P.O. once daily (extended-release). Adjust dosage at 7- to 14-day intervals based on patient tolerance and response. Maximum dose is 120 mg daily.

Pharmacodynamics
Antianginal action: Nifedipine dilates systemic arteries, resulting in decreased total peripheral resistance and modestly decreased systemic blood pressure with a slightly increased heart rate, decreased afterload, and increased cardiac index. Reduced afterload and the subsequent decrease in myocardial oxygen consumption probably account for the value of nifedipine in treating chronic stable angina. In Prinzmetal’s angina, nifedipine inhibits coronary artery spasm, increasing myocardial oxygen delivery.

Pharmacokinetics
Absorption: About 90% of a dose is absorbed rapidly from the GI tract after oral administration; however, only about 65% to 70% of drug reaches the systemic circulation because of a significant first-pass effect in the liver. Therapeutic serum levels are 25 to 100 ng/ml.
Distribution: About 92% to 98% of circulating nifedipine is bound to plasma proteins.
Metabolism: Metabolized in the liver.
Excretion: Excreted in urine and feces as inactive metabolites. Elimination half-life is 2 to 5 hours.

Contraindications and precautions
Contraindicated in patients hypersensitive to drug. Use cautiously in elderly patients and patients with heart failure or hypotension.
  Use cautiously in patients with unstable angina who aren’t currently taking a beta blocker because a higher risk of MI has been reported. Use extended-release form cautiously in patients with GI narrowing.

Interactions
Drug-drug. Beta blockers: May worsen angina, heart failure, and hypotension. Use together cautiously.
Cimetidine: May decrease nifedipine metabolism. Use together cautiously.
Digoxin: May increase serum digoxin levels. Monitor serum digoxin level.
Fentanyl: May cause excessive hypotension. Use together cautiously.
Hypotensive drugs: May precipitate excessive hypotension. Use together cautiously.
Phenytoin: May increase phenytoin levels. Monitor phenytoin levels.
Drug-herb. Melatonin: Interferes with antihypertensive effect of nifedipine. Discourage use together.
Drug-food. Grapefruit juice: Increases bioavailability of drug. Advise patient to avoid taking drug with grapefruit juice.

Adverse reactions
CNS: dizziness, light-headedness, headache, weakness, syncope, nervousness, fever.
CV: peripheral edema, hypotension, palpitations, heart failure, MI, flushing.
EENT: nasal congestion.
GI: nausea, diarrhea, constipation, abdominal discomfort.
Hepatic: liver dysfunction.
Metabolic: hypokalemia.
Musculoskeletal: muscle cramps.
Respiratory: dyspnea, cough, pulmonary edema.
Skin: rash, pruritus.

Effects on lab test results
• May increase ALT, AST, alkaline phosphatase, and LDH levels. May decrease potassium level.

Overdose and treatment
Effects of overdose are extensions of pharmacologic effects, primarily peripheral vasodilation and hypotension.
 Treatment includes such basic support measures as hemodynamic and respiratory monitoring. If patient needs blood pressure support with a vasoconstrictor, norepinephrine may be given. Elevate limbs and correct any fluid deficit.

Special considerations
• Nifedipine has been used investigationally to treat Raynaud’s phenomenon and preterm labor.
 ALERT Warn patient not to switch brands. Procardia XL and Adalat CC aren’t therapeutically equivalent because of major differences in their pharmacokinetics.
• Initial doses and increased dosage may worsen angina briefly. Reassure patient that this effect is temporary.
• No advantage has been found in S.L. or intrabuccal nifedipine use.
• Monitor blood pressure regularly, especially if patient is also taking beta blockers or antihypertensives.
• Although rebound effect hasn’t been observed when drug is stopped, reduce dosage slowly.
Geriatric patients
• Use drug cautiously in geriatric patients because they may be more sensitive to effects of drug and duration of effect may be prolonged. Orthostatic blood pressures should be monitored.

Patient education
• Instruct patient to swallow capsules whole without breaking, crushing, or chewing them unless instructed otherwise.
• Tell patient that he may experience annoying hypotensive effects early in therapy and during dosage adjustment; urge compliance with therapy.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use