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. (Adalat XL and amlodipine)
- The nondihydropyridines – cause blood vessels to dilate and slows down the electrical conduction in the heart. (verapamil and diltilazem)
Both types work by blocking the entry of calcium into the smooth muscle of the blood vessels. This causes the blood vessels to dilate so that blood pressure is lowered and blood flow is subsequently improved to the heart. For this reason they are very useful in treatment of angina and are the drugs of choice for Prinzmetal’s angina (spasm of the coronary arteries). The nondihydropyridines slow the electrical conduction of the heart and cause heart block, especially if combined with beta-blockers. They also limit the intake of calcium into the muscle of the heart and reduce the force of contraction, and should be used with caution in patients with heart failure.
Who benefits from calcium channel blockers?
The calcium channel blockers are particularly effective in the elderly and patients with systolic hypertension, and are more effective in stroke protection compared to other antihypertneives,
Due to the vasodilation calcium antagonists are very useful in the treatment of angina, Prinzmetal’s angina and peripheral vascular disease (narrowed arteries in the legs).
The nondihydropyridines not only dilate blood vessels, but also affect the muscle and electrical activity of the heart. Therefore these drugs can be helpful in treating patients with rapid heart rates or tachyarrhythmias.
Compelling indications for use as anti-hypertensive drug:
- Elderly patients
- In patients with systolic hypertension
- African patients
- 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 (non-dihydropyridine only)
- Preganncy (nifedipine only)
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 (non-dihydropyridines only)
- Congestive heart failure
- In patients using beta-blockers (non-dihydropyridines only)
Possible side effects
Oedema of legs especially females
- Headache and flushing
- Gum overgrowth (rare)
- Short acting nifedipines cause sudden drops in blood pressure and are linked to increased heart attack risk. (avoid)
Possible drug interactions
- Calcium antagonists, (nondihydropyridines) cannot be taken with beta-blockers.
- The grapefruit juice can affect the liver’s ability to metabolize some of the calcium antagonists. Do not drink this for two hours before of after taking these drugs, to prevent toxic accumulation.
- Non-dihydropyridiine calcium antagonists can increase the effect of digoxin.
- Antiretrovirals (dihydropyridine)
Article written by Dr Kathleen Coetzee, MBChB
Reviewed by Prof Brian Rayner, head of the division of nephrology and hypertension, University of Cape Town and Groote Schuur Academic Hospital, December 2010
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