Calcium antagonists

Question 1

Indications

Answer 1

1. Amlodipine and, to a lesser extent, nifedipine are used for the first- or second-line treatment of hypertension, to reduce the risk of stroke, myocardial infarction and death from cardiovascular disease.
2. All calcium channel blockers can be used to control symptoms in people with stable angina; β-blockers are the main alternative.
3. Diltiazem and verapamil are used to control cardiac rate in people with supraventricular arrhythmias including supraventricular tachycardia, atrial flutter and atrial fibrillation.

Question 2

Mechanism of action

Answer 2

Calcium channel blockers decrease Ca2+ entry into vascular and cardiac cells, reducing intracellular calcium concentration. This causes relaxation and vasodilation in arterial smooth muscle, lowering arterial pressure. In the heart, calcium channel blockers reduce myocardial contractility. They suppress cardiac conduction, particularly across the atrioventricular (AV) node, slowing ventricular rate. Reduced cardiac rate, contractility and afterload reduce myocardial oxygen demand, preventing angina.

Question 3

Adverse effects

Answer 3

Ankle swelling
Flushing
Headache
Palpitations

Question 4

Warnings

Answer 4

Verapamil and diltiazem should be used with caution in patients with poor left ventricular function as they can precipitate or worsen heart failure. They should generally be avoided in people with AV nodal conduction delay in whom they may provoke complete heart block. Amlodipine and nifedipine should be avoided in patients with unstable angina as vasodilatation causes a reflex increase in contractility and tachycardia, which increases myocardial oxygen demand. In patients with severe aortic stenosis, amlodipine and nifedipine should be avoided as they can provoke collapse.

Question 5

Interactions

Answer 5

Non-dihydropyridine calcium channel blockers (verapamil and diltiazem) should not be prescribed with β-blockers except under close specialist supervision. Both drug classes are negatively inotropic and chronotropic, and together may cause heart failure, bradycardia, and even asystole.

Question 6

Prescribing

Answer 6

PO

Question 7

Administration

Answer 7

Modified-release and long-acting preparations should be swallowed whole, and not crushed or chewed as this will interfere with the slow release of the drug.

Question 8

Communication

Answer 8

Explain why the calcium channel blocker has been prescribed depending on indication. As appropriate, discuss other measures to reduce cardiovascular risk, including smoking cessation. Discuss common side effects, particularly ankle oedema if relevant.

Question 9

Monitoring

Answer 9

Treatment efficacy can be judged by regular blood pressure monitoring for hypertension, enquiry about chest pain for angina and by pulse rate from examination or ECG. A 24-hour tape can be performed to review arrhythmias.