What is it and how does it work?

Also called calcium antagonists, these drugs are divided into two types:

• The dihydropyridines – cause blood vessels to dilate.
• The nondihydropyridines – cause blood vessels to dilate and slows down the electrical conduction in the heart.

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Both types work by blocking the entry of calcium into the smooth muscle of the blood vessels. This causes the blood vessels to dilate and blood pressure is lowered. The nondihydropyridines also limit the intake of calcium into the muscle of the heart. The vasodilation increases blood supply to the heart. For this reason it can be helpful in patients with angina (chest pain due to inadequate oxygen supply to the heart).

A few calcium channel blockers

• Nifedipine in Adalat.
• Verapamil in Isoptin.
• Diltiazem in Tilazem.

Who benefits from calcium channel blockers?

The calcium channel blockers are particularly effective in the elderly and patients with systolic hypertension. It is also of benefit in the prevention of stroke in these patients.

Due to the vasodilation some calcium antagonists are sometimes used in patients with narrowed arteries in the legs.

The nondihydropyridines not only dilates blood vessels, but also affects the muscle and electrical activity of the heart. Therefore these drugs can be helpful in treating patients with angina.

Compelling indications for use as anti-hypertensive drug:

• Angina (nondihydropyridines).
• Elderly patients.
• In patients with systolic hypertension.
• African patients.

Possible indications:

• Peripheral vascular disease (poor circulation to the legs).
• After a heart attack – sometimes nondihyropyridines are used if beta-blockers are contraindicated.
• Certain types of irregularity of heart rhythm.
• Migraine (nondihydropyridines).

Who should not take calcium channel blockers?
The nondihydropyridines slow the electrical conduction in the heart, and should therefore never be used in patients where the conduction is impaired or if heart failure is present. Patients using beta-blockers also cannot take these drugs.

Contraindications or caution:

• Heart block.
• Congestive heart failure.
• In patients using beta-blockers.

Possible side effects
The nondihydropyridines may cause constipation, and the dihydropyridines can increase the heart rate. Other side effects include swelling of the legs and feet, skin rash and headaches.

Dihydropyridines that are short-acting can lead to a rapid and pronounced drop in blood pressure. This could put a patient with heart disease at risk for stroke or heart attack. Long- acting dihydropyridines have been developed that produces a slow decline in blood pressure and 24 hour control. These drugs are safe to use even in patients with heart disease.

Possible drug interactions

• Calcium antagonists, especially nondihydropyridines, cannot be taken with beta-blockers.
• The juice of grapefruit can affect the liver’s ability to metabolize some of the calcium antagonists. Do not drink it for two hours before of after taking these drugs to prevent toxic accumulation.
• Some calcium antagonists can increase the effect of digoxin.

Written by Dr Kathleen Coetzee, MBChB.

Read more:
Genes, diet and disease
Hypertension in SA

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