Calcium Channel Blockers

Calcium Channel Blockers (CCBs)

• Definition: Medications that treat hypertension, cardiac dysrhythmias, and angina pectoris; also known as slow channel blockers or calcium antagonists.

Therapeutic Uses

• Types of CCBs:

  • Arteriolar-Specific: Primarily affect peripheral arterioles (e.g., dihydropyridines).

  • Dual-Action: Affect both arterioles and heart arteries.

• Key Uses:

  • Treat mild to moderate hypertension.

  • Certain CCBs also treat cardiac dysrhythmias and angina pectoris.

Prototype and Other Medications

• Nifedipine: Primarily affects arterioles.

• Verapamil: Affects both arterioles and heart arteries, also discussed under cardiac dysrhythmias.

• Other CCBs: Diltiazem, amlodipine, felodipine, isradipine, nicardipine, nisoldipine.

Expected Pharmacologic Action

• Dihydropyridines:

  • Significantly block calcium channels in vascular smooth muscle cells.

  • Minimal effects on cardiac arteries, leading to:

    • Vasodilation: Results in lowered blood pressure.

    • Reflex Tachycardia: Indirect increase in heart rate due to baroreceptor reflex without direct cardiac effects.

Adverse Drug Reactions

• Common Side Effects:

  • Reflex Tachycardia: Can exacerbate angina pain, particularly with fast-acting forms.

  • Vasodilatory Effects:

    • Headaches, lightheadedness, dizziness, facial flushing, perception of heat, peripheral edema.

  • Less Common Effects:

    • Arrhythmias, gingival hyperplasia, bleeding gums.

Interventions

• Administration:

  • Administer with beta-blockers to prevent tachycardia.

  • Monitor heart rate even if a beta-blocker is prescribed.

  • Watch for lightheadedness/dizziness; assist with ambulation as needed.

  • Inform clients about potential facial flushing.

• Blood Pressure Monitoring:

  • Monitor closely, especially during dosage establishment.

  • Withhold medication for systolic BP < 90 mm Hg and notify provider.

• Dental Hygiene:

  • Advise regular dental checkups and good hygiene practices.

Administration

• Nifedipine Forms:

  • Available in oral capsules and extended-release tablets.

  • Some dihydropyridine CCBs available in IV form.

  • Extended-release forms approved for essential hypertension; must not be chewed or crushed.

Client Instructions

• Reporting Symptoms:

  • Report rapid heartbeat and increased angina pain.

  • Notify provider if heart rate drops below 50 bpm.

• Safety Precautions:

  • Avoid hazardous activities (e.g., driving) until effects are known.

  • Be aware of facial flushing and possible feelings of heat.

  • Report swelling (feet/legs), dizziness, or syncope.

  • Follow prescribed dosage and avoid self-increases due to hypotension risk.

• Dental Care:

  • Maintain good dental hygiene and report gum issues.

• Dietary Restrictions:

  • Avoid grapefruit/grapefruit juice during therapy.

Contraindications and Precautions

• Contraindications:

  • Not for children; sensitivity to medication; systolic BP < 90 mm Hg.

  • Second or third-degree AV block or sick sinus syndrome.

  • Concurrent use with grapefruit and certain medications (e.g., rifampin, phenytoin).

• Use Caution:

  • Severe renal/hepatic impairment, history of heart failure, severe ventricular arrhythmias, geriatric patients.

Interactions

• With Beta-Blockers:

  • Risk of heart failure but may prevent reflex tachycardia.

• Contraindicated Medications:

  • Rifampin, rifabutin, phenobarbital, phenytoin, carbamazepine reduce efficacy of nifedipine.

  • Avoid St. John’s wort; reduces therapeutic effects.

• Grapefruit Juice:

  • Increases blood levels of CCBs and risk of adverse effects.

Safety Alert

• CYP3A4 Inhibition:

  • Grapefruit juice inhibits CYP3A4, increasing medication concentrations, risking toxicity and side effects in CCBs, amiodarone, buspirone, and diphenhydramine.