Pharmacology II: Calcium Channel Blockers

Calcium Channel Blockers

• Used to prevent angina that doesn't respond to other antianginal classes, as well as antiarrhythmics and in the treatment of hypertension.
• Examples of calcium channel blockers include amlodipine besylate, diltiazem, nicardipine, nifedipine, and verapamil.

Pharmacokinetics

• Absorbed quickly and almost completely when administered orally.
• Bioavailability is lower due to the first-pass effect.
• Highly bound to plasma proteins.
• Metabolized rapidly and almost completely in the liver.

Pharmacodynamics

• Prevent the passage of calcium ions across the myocardial cell membrane and vascular smooth-muscle cells.
• Causes dilation of the coronary and peripheral arteries, decreasing the force of the heart's contractions and reducing the workload of the heart.
• Reduces afterload, resulting in a decreased oxygen demand of the heart.
• Some calcium channel blockers (diltiazem and verapamil) also reduce the heart rate by slowing conduction through the SA and AV nodes.

Pharmacotherapeutics

• Used only for long-term prevention of angina, not for short-term relief of chest pain.
• Particularly effective for preventing Prinzmetal's angina.

Drug Interactions

• Calcium salts and vitamin D reduce the effectiveness of calcium channel blockers.
• Verapamil and diltiazem increase the risk of digoxin toxicity and enhance the action of carbamazepine.

Adverse Reactions

• Headache
• Dizziness
• Weakness
• Orthostatic hypotension
• Heart failure
• Hypotension
• Peripheral edema
• Palpitations
• Arrhythmias such as tachycardia, bradycardia, and AV block (also occur with diltiazem and verapamil)

Assessment

• Obtain a history of the patient's underlying condition before therapy and reassess regularly.
• Obtain a baseline blood pressure and pulse rate and rhythm; recheck regularly.
• Monitor the ECG when therapy starts and when the dosage is adjusted.
• Monitor the patient's vital signs frequently and assess for signs of toxicity and adverse reactions.

Key Nursing Diagnoses

• Risk for injury related to orthostatic hypotension.
• Risk for injury related to adverse reactions.
• Deficient knowledge related to drug therapy.

Planning Outcome Goals

• Risk for injury will be minimized.
• Complications from adverse reactions will be diminished.
• The patient will verbalize an understanding of drug therapy.

Implementation

• Don't crush sustained-release tablets.
• Be aware that sustained-release and extended-release medications aren't interchangeable.
• Take safety precautions if adverse CNS reactions occur.
• Withhold the dose and notify the prescriber if the patient's systolic pressure is below 90 mmHg or their heart rate drops below 60 beats/minute.