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Calcium Entry Blockers Drugs Blocking Calcium Channels in Heart Muscle: Verapamil (isoptin), Nifedipine (Nicardia), Diltiazem (Dilzem) These drugs (except nifedipine) block the calcium channels in the cells of the heart muscles and blood vessels, causing decreased contraction of the heart muscles and dilation of the blood vessels in the body and heart. Of these, the first three are used widely in clinical practice. Although all three of them are potent coronary vasodilators, they differ in their action on the blood vessels and the contraction of the heart. Nifedipine is a more potent vasodilator than either verapamil or diltiazem, Similarly, verapamil inhibits the contraction of the heart more than that of nifedipine or diltiazem. Verapamil (Isoptin) It reduces anginal attacks by relieving the coronary artery spasm, increasing oxygen supply, and reducing the oxygen demand by decreasing the heart rate and reducing after-load (back pressure of blood from the body to the heart). Verapamil is effective in angina prevention in dose of 40-80 mg, 3 times a day. It is also useful in slowing very rapid heart rates in paoxysmal Atrial Tachycardia (PAT). Adverse Effects: Constipation is the most common adverse effect of verapamil. It may cause headache, vertigo, weakness, nervousness, gastric upsets, and allergy in the form of itching, flushing or rash, and decreased pumping action of the heart (congestive heart failure). Rebound angina may occur following a sudden withdrawal of verapamil. Heart blocks may occur, however occurance of heart arrest is rare. Precautions Do not use it with a beta blockers quinidine or disopyramide. It can be a dangerous combination. Digoxin levels in the blood increase when verapamil is taken along with it. These drugs should be used cautiously if taken together. Rifampicin and other drugs which stimulate or induce the enzymes in liver, decrease the effect of verapamil. The doses of verapamil should be adjusted when given with them. It is found in human milk and should be avoided during pregnancy and breast feeding. In patients with severely impaired liver function, its dose should be reduced to 30%. Nifedipine (Nicardia, Nicardia-CD, Calcigard Retard) This has a potent vasodilator property with little depressant effect on the heart. It prevents coronary artery spasms but may promote 'coronary steal' (diversion of blood flow from the occlude coronary artery to a healthy area of the heart). Due to its relatively selective action on the vascular smooth muscles, it reduces the blood pressure and may sometimes cause a reflex increase in the heart rate. It increases oxygen supply to the heart muscle by relieving coronary artery spasms and decreases demand by reducing the after-load (back pressure of blood from the body to the heart). The beneficial effect of nifedipine in angina is mostly because of the latter action. The usual dose is 10 to 20 mg, 3 to 4 times a day. Retard preparations are given twice a day. Long acting preparations (NICARDIA CD) do not cause that much tachycardia and are preferred. Many other longer acting alternatives such as amlodipine (2.5 mg, 5 mg), nitrendipine (10 mg, 20 mg) and felodipine (2.5 mg, 5 mg) are also available. Adverse Effects: Nifedipine may cause headache, palpitation, dizziness, weakness, nausea, flushing, a transient decrease in blood pressure, and allergic skin reaction. Swelling of the feet due to vasodilation is common. Precautions If the attack continues to be frequent and severe, other anti-anginal drugs may be substituted. If a blackout or any visual disturbances (due to reduction in blood supply) occur, the drug should be stopped and the doctor consult. Diabetic patients should get their blood sugar checked more frequently as the drug may, at times, elevate blood glucose levels. The drug should not be withdrawn suddenly as this may cause a rebound attack of angina.
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