Understanding Cardiovascular Medications

Since the heart is a muscle that must work continuously, it requires a constant supply of nutrients and oxygen. Those nutrients and oxygen are carried to the heart muscle in the blood. The chest pain known as angina can occur when there is an insufficient supply of blood, and consequently of oxygen, to the heart muscle.

There are several types of antianginal medications. These include beta blockers (acebutolol, atenolol, betaxolol, bisoprolol, labetalol, metoprolol, nadolol, pindolol, propranolol, timolol), calcium channel blockers (diltiazem, nifedipine, verapamil), and vasodilators (nitroglycerin, isosorbide dinitrate). These drugs act by increasing the amount of oxygen that reaches the heart muscle.

If the heart does not beat rhythmically or smoothly (a condition called arrhythmia), its rate of contraction must be regulated. Antiarrhythmic drugs (disopyramide, mexiletine, procainamide, propranolol, amiodarone, tocainide) prevent or alleviate arrhythmias by altering nerve impulses in the heart.

The blood has a natural ability to clot; otherwise, we would bleed to death from the slightest wound. Sometimes, however, this natural clotting mechanism can be problematic; for instance, blood clots that develop on the interior wall of an artery can end up completely blocking blood flow. Drugs that prevent blood clotting are called anticoagulants (blood thinners). Anticoagulants fall into two categories.

The first category contains medications that must be given by injection. These medications are used in both the hospital and home-care settings. They work by preventing or treating blood clots that could interfere with circulation. Examples of such drugs are dalteparin, enoxaparin, and heparin.

The second category includes oral anticoagulants (those taken by mouth), principally derivatives of the drug warfarin. Warfarin may be used in the treatment of conditions such as stroke, heart disease, and abnormal blood clotting. Warfarin is also used to prevent the movement of a clot, a development that could cause serious problems. It acts by preventing the liver from manufacturing the proteins that are responsible for blood clot formation.

People who are taking warfarin must be careful to avoid using many other medications (including certain doses of aspirin, which itself can have a blood thinning effect), because the interaction of the other medications with the anticoagulant medication could cause internal bleeding. Indeed, patients who are taking warfarin should check with their pharmacist or physician before using any other medications, including any herbal products; natural or homeopathic remedies; vitamins, minerals, or other supplements; and any over-the-counter medications. People taking warfarin should also have their blood checked frequently by their physician to ensure that the correct degree of blood thinning is maintained.

Medications for treating atherosclerosis, or hardening of the arteries, act to reduce the serum (the liquefied portion of blood) levels of cholesterol and triglycerides (fats), which form plaques (deposits) on the walls of arteries. Some antihyperlipidemics, such as cholestyramine, colestipol, and colesevelam, bind to bile acids in the gastrointestinal tract, thereby decreasing the body's production of cholesterol. Atorvastatin, simvastatin, lovastatin, and pravastatin also decrease the body's production of cholesterol.

Use of such drugs is generally recommended only after diet and lifestyle changes have failed to lower blood lipids to desirable levels. Even then, however, diet therapy should be continued.

Basically, high blood pressure is a condition in which the pressure of the blood against the walls of the blood vessels is higher than what is considered normal. High blood pressure, or hypertension, which can eventually cause damage to the brain, eyes, heart, or kidneys, is controllable. If medication for high blood pressure has been prescribed, it is very important that you continue to take it regularly, even if you don't notice any symptoms of hypertension. If hypertension is controlled, other damage can be prevented. Medications that counteract or reduce high blood pressure can prolong the life of people with hypertension.

Several different drug actions produce an antihypertensive effect. Some drugs block nerve impulses that cause arteries to constrict; others slow the heart rate and decrease its force of contraction; still others reduce the amount of a certain hormone in the blood that causes blood pressure to rise. The effect of any of these medications is to reduce blood pressure. The mainstay of antihypertensive therapy is often a diuretic, a drug that reduces body fluids.

Examples of antihypertensive drugs include beta blockers, calcium channel blockers, ACE (angiotensin-converting enzyme) inhibitors (including benazepril, captopril, enalapril, lisinopril, and quinapril), and the agents valsartan, losartan, prazosin, and terazosin.

Beta-blocking medications block the response of the heart and blood vessels to nerve stimulation, thereby slowing the heart rate and lowering blood pressure. They are used in the treatment of a wide range of diseases, including angina, high blood pressure, migraine headaches, arrhythmias, and glaucoma. Metoprolol and propranolol are examples of beta blockers.

Calcium channel blockers (diltiazem, nifedipine, verapamil) are used for the prevention of angina (chest pain). Verapamil is also useful in correcting certain arrhythmias (heartbeat irregularities) and lowering blood pressure. This group of drugs is thought to prevent angina and arrhythmias and lower blood pressure by blocking or slowing calcium flow into muscle cells, which results in vasodilation (widening of the blood vessels) and greater oxygen delivery to the heart muscle.

Cardiac glycosides include drugs that are derived from digitalis (digoxin is an example). This type of drug slows the rate of the heart but increases its force of contraction. Cardiac glycosides act as both heart depressants and stimulants: They may be used to regulate irregular heart rhythm or to increase the volume of blood pumped by the heart in heart failure.

Diuretic drugs, such as chlorothiazide, chlorthalidone, furosemide, hydrochlorothiazide, and spironolactone, promote the loss of water and salt from the body (which is why they are sometimes called water pills). This loss of water and salt results in lower blood pressure. They also lower blood pressure by increasing the diameter of blood vessels.

Because some antihypertensive medications cause the body to retain salt and water, they are often used concurrently with diuretics. Most diuretics act directly on the kidneys, but there are different types of diuretics, each with different actions. This allows therapy for high blood pressure to be adjusted to meet the needs of individual patients.

Thiazide diuretics, such as chlorothiazide, chlorthalidone, and hydrochlorothiazide, are the most commonly prescribed water pills available today. They are generally well tolerated and can be taken either once or twice per day. Since patients do not develop a tolerance to their antihypertensive effect, these diuretics can be taken for prolonged periods.

However, a major drawback of thiazide diuretics is that they often deplete the body of potassium. This can be compensated for with a potassium supplement. Potassium-rich foods and liquids, such as apricots, bananas, and orange juice, can also be used to help correct a potassium deficiency. Salt substitutes are another source of potassium. If necessary, your doctor will direct you to a source of potassium appropriate for you.

Loop diuretics, such as furosemide, act more vigorously than thiazide diuretics. (Loop refers to the structures in the kidneys on which these specific diuretic medications act.) Loop diuretics promote more water loss than thiazide diuretics but they also deplete more potassium from the body.

To remove excess water from the body while retaining its store of potassium, manufacturers developed potassium-sparing diuretics. Medications such as amiloride, spironolactone, and triamterene are effective in treating potassium loss, heart failure, and high blood pressure. Potassium-sparing diuretics are combined with thiazide diuretics in combination medications such as amiloride and hydrochlorothiazide combination, spironolactone and hydrochlorothiazide combination, and triamterene and hydrochlorothiazide combination. Such blends of drugs enhance the antihypertensive effect and reduce potassium loss.

Vasodilating medications cause the blood vessels to dilate, or widen. Some of the antihypertensive medications, such as hydralazine and prazosin, lower blood pressure by dilating the arteries or veins. Other vasodilating medicines are used in the treatment of stroke and diseases that are characterized by poor blood circulation. Ergoloid mesylates, for example, are used to reduce the symptoms of senility by increasing the flow of oxygen-rich blood to the brain.