Calcium channel blockers
Calcium channel blockers
Based on differences in chemical structure and activity, the calcium antagonists are categorised into three groups:
All calcium antagonists have negative chronotropic and negative dromotropic effects. Verapamil and diltiazem also have negative inotropic effects. These drugs block influx of Ca2+ into the cell. Ca2+ is required for contraction of all muscle cells. Skeletal muscles have sufficient intracellular calcium, whereas the myocardium and smooth muscles in arterial vessels depend on influx of Ca2+. Decreased influx of Ca2+ diminishes the release of Ca2+ from the sarcoplasmic reticulum. Hence, contractility of the myocardial cells is decreased. Another effect of the decreased Ca2+ levels is a slower electrical conduction in the SA and AV nodes. The effect of calcium antagonists (mainly dihydropyridines) on smooth muscles in vessel walls results in vasodilation.
Angina pectoris and hypertension are the main indications for use of calcium antagonists. Because of their negative inotropic effects, verapamil and diltiazem are contraindicated in patients with heart failure.
General adverse effects include headache, flushing, and dizziness due to the vasodilating effects. Hypotension, palpitations, gastrointestinal complaints, and oedema in the ankles also occur. Verapamil has constipation as specific side effect. Symptoms of overdosing are similar. Furthermore, sinus bradycardia, disorders of the AV conductance, and coma have been reported. Activated charcoal and laxatives can be taken to inhibit further uptake of the drug. Intervention with calcium chloride solution or glucagon (positive inotropic and chronotropic) is useful when the drug is already available to the body.
Co-treatment of calcium antagonists (especially verapamil and diltiazem) and α-blockers should be avoided. The combined effects have a high risk of hypotension, heart failure, and conductance disorders.
Mrs V has hypertension and depression. She is taking amlodipine 10 mg dd and seroxat 20 mg dd. Her BP is now 110/65 mm Hg. She complains of swelling in her ankles. How will you manage her hypertension?
Extra info: Mrs V has become hypotensive, so her dosing of amlodipine is too high. The side effect of pedal oedema may also improve with a lower dosage.
Calcium antagonists are used in patients with angina in all the following cases, EXCEPT:
Extra info: Close In cases of asthma and diabetes, β-blockers are not first line therapy for angina, an thus calcium antagonists are indicated. In addition, calcium antagonists are shown to decrease risk of mortality in Prinzmetal's angina, where as β-blockers can be deleterious.
Side effects for calcium antagonists include all of the following EXCEPT
Contraction of the myocardium depends on
Extra info: Calcium ions are responsible for the contraction of muscle.