CD-ROM Today 1996 January

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$Unique_ID{BRK02990} $Pretitle{} $Title{The New Prescription Drug Reference Guide - How Drugs Work, part I} $Subject{Types CARDIOVASCULAR Antianginals Antiarrhythmics Antihypertensives Diuretics Cardiac Glycosides Anticoagulants Antihyperlipidemics Vasodilators Beta Blockers Calcium Channel Blockers EARS EYES GASTROINTESTINAL Antinauseants Anticholinergics Antiulcer Antidiarrheals HORMONES Thyroid Antidiabetic Steroids Sex Hormones ANTI-INFECTIVES Antibiotics Antivirals Vaccines anthelmintics pediculicide scabicide ANTINEOPLASTICS TOPICAL CENTRAL NERVOUS SYSTEM Sedatives Tranquilizers Antidepressants Amphetamines Anticonvulsants Antiparkinsonism Agents Analgesics Anti-Respiratory Antitussives Expectorants Decongestants Bronchodilators Antihistamines VITAMINS MINERALS} $Volume{} $Log{} Copyright (C) 1993 Publications International, Ltd. How Drugs Work, part I ------------------------------------------------------------------------------ Prescription drugs fall into a number of groups according to the conditions for which they are prescribed. In the following pages, we will provide you with a better understanding of the types of medications that are prescribed for different medical conditions. We'll describe the intended actions of drugs and the therapeutic effects you can expect from various types of medications. CARDIOVASCULAR DRUGS Antianginals Since the heart is a muscle that must work continuously, it requires a constant supply of nutrients and oxygen. The chest pain known as angina can occur when there is an insufficient supply of blood, and consequently of oxygen, to the heart. There are several types of antianginal drugs. These drugs include vasodilators (nitroglycerin, isosorbide dinitrate), calcium channel blockers (diltiazem, nifedipine, verapamil), and beta blockers (acebutolol, atenolol, labetalol, metoprolol, nadolol, pindolol, propranolol, timolol). All of these drugs act by increasing the amount of oxygen that reaches the heart muscle. Antiarrhythmics 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, tocainide, quinidine) prevent or alleviate cardiac arrhythmias by altering nerve impulses within the heart. Antihypertensives Briefly, 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 a 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. Drugs that counteract or reduce high blood pressure can prolong a hypertensive patient's life. 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 (aldosterone) in the blood that causes blood pressure to rise. The effect of any of these is to reduce blood pressure. The mainstay of antihypertensive therapy is often a diuretic, a drug that reduces body fluids. Examples of additional antihypertensive drugs include clonidine, hydralazine, methyldopa, prazosin, and reserpine. Diuretics Diuretic drugs, such as chlorothiazide, chlorthalidone, furosemide, hydrochlorothiazide, and spironolactone, promote the loss of water and salt from the body (this is why they are sometimes called "water pills"). This loss of water and salt results in lowering of blood pressure. They also lower blood pressure by increasing the diameter of blood vessels. Because many antihypertensive drugs 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. Thus, therapy for high blood pressure can be individualized for each patient's needs. 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 once or twice a day. Since patients do not develop a tolerance to their antihypertensive effect, they can be taken for prolonged periods. However, a major drawback to thiazide diuretics is that they often deplete the body of potassium. This depletion can be compensated for with a potassium supplement. Potassium-rich foods and liquids, such as bananas, apricots, and orange juice, can also be used to help correct the potassium deficiency. Salt substitutes are another source of potassium. Your doctor will direct you as to which source of potassium, if any, is appropriate for you to use. Loop diuretics, such as furosemide, act more vigorously than thiazide diuretics. (The term "loop" refers to the structures in the kidneys on which these medications act.) Loop diuretics promote more water loss but also deplete more potassium. To remove excess water from the body but retain its store of potassium, manufacturers developed potassium-sparing diuretics. Drugs such as spironolactone, triamterene, and amiloride are effective in treating potassium loss, heart failure, and hypertension. Potassium-sparing diuretics are combined with thiazide diuretics in medications such as spironolactone and hydrochlorothiazide combination, triamterene and hydrochlorothiazide combination, and amiloride and hydrochlorothiazide combination. Such combinations enhance the antihypertensive effect and reduce the loss of potassium. They are now among the most commonly used antihypertensive agents. Cardiac Glycosides Cardiac glycosides include drugs that are derived from digitalis (for example, digoxin and digitoxin). This type of drug slows the rate of the heart but increases its force of contraction. Cardiac glycosides, therefore, act as both heart depressants and stimulants and may be used to regulate irregular heart rhythm or to increase the volume of blood pumped by the heart in heart failure. Anticoagulants Drugs that prevent blood clotting are called anticoagulants (blood thinners). Anticoagulants fall into two categories. The first category contains only one drug, heparin. Heparin must be given by injection, so its use is generally restricted to hospitalized patients. The second category includes oral anticoagulants, principally derivatives of the drug warfarin. Warfarin may be used in the treatment of conditions such as stroke, heart disease, and abnormal blood clotting. It is also used to prevent the movement of a clot, which could cause serious problems. It acts by preventing the liver from manufacturing the proteins responsible for blood clot formation. Persons taking warfarin must avoid using many other drugs (including aspirin), because their interaction with the anticoagulant could cause internal bleeding. Patients taking warfarin should check with their pharmacist or physician before using any other medications, including over-the-counter products for coughs or colds. In addition, they must have their blood checked frequently by their physician to ensure that the drug is maintaining the correct degree of blood thinning. Antihyperlipidemics Drugs used to treat atherosclerosis (arteriosclerosis, or hardening of the arteries) act to reduce the serum (the liquified portion of blood) levels of cholesterol and triglycerides (fats), which form plaques (deposits) on the walls of arteries. Some antihyperlipidemics, such as cholestyramine and colestipol, bind to bile acids in the gastrointestinal tract, thereby decreasing the body's production of cholesterol. Clofibrate and probucol 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, diet therapy should be continued. Vasodilators Vasodilating drugs cause the blood vessels to dilate (widen). Some of the antihypertensive agents, such as hydralazine and prazosin, lower blood pressure by dilating the arteries or veins. Other vasodilators are used in the treatment of stroke and diseases characterized by poor circulation. Ergoloid mesylates, for example, are used to reduce the symptoms of senility by increasing blood flow to the brain. Beta Blockers Beta-blocking drugs block the response of the heart and blood vessels to nerve stimulation, thereby slowing the heart rate and reducing high blood pressure. They are used in the treatment of a wide range of diseases including angina, hypertension, migraine headaches, and arrhythmias. Propranolol and metoprolol are two examples of beta blockers. Calcium Channel 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 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. DRUGS FOR THE EARS For an ear infection, a physician usually prescribes an antibiotic and a steroid, or a medication that contains a combination of these. The antibiotic attacks the infecting bacteria, and the steroid reduces the inflammation and pain. Often, a local anesthetic, such as benzocaine or lidocaine, may also be prescribed to relieve pain. DRUGS FOR THE EYES Almost all drugs that are used to treat eye problems can be used to treat disorders of other parts of the body as well. Glaucoma is one of the major disorders of the eye, especially in people over 40 years of age, and results in increased pressure within the eyeball. Although glaucoma is sometimes treated surgically, pressure in the eye can usually be reduced, and blindness prevented, through use of eye drops. Two drugs frequently prescribed as eye drops are epinephrine and pilocarpine. Pilocarpine is a cholinergic drug. Cholinergic drugs act by stimulating parasympathetic nerve endings. Stimulation of these nerve endings alters the activity of many organs throughout the body. For example, a cholinergic drug can cause the heart rate to decrease, intestinal activity to increase, and the bronchioles within the lungs to constrict. When used in the eyes, pilocarpine causes constriction of the pupils and increases the flow of aqueous humor (fluid) out of the eye, thereby reducing the pressure. Epinephrine is a newer name for the body chemical called adrenaline. Epinephrine is secreted in the body when one must flee from danger, resist attack, or combat stress. Epinephrine has adrenergic properties, such as increasing the amount of sugar in the blood, accelerating the heartbeat, and dilating the pupils. The mechanism by which epinephrine lowers pressure within the eye is not completely understood, but it appears to involve both a decrease in the production of aqueous humor and an increase in the outflow of this fluid from the eye. Antibiotics are used to treat bacterial eye infections. Steroids can also be used to treat noninfectious eye inflammations, as long as these medications are not used for too long a period of time. Pharmacists carefully monitor requests for eye drop refills, particularly for drops that contain steroids, and may refuse to refill such medication until you have revisited your doctor because these products can cause further eye problems with long-term use. GASTROINTESTINAL DRUGS Antinauseants Antinauseants reduce the urge to vomit. One of the most effective antinauseants is the phenothiazine derivative prochlorperazine. This medication acts on the vomiting center in the brain. It is often administered rectally and usually alleviates nausea and vomiting within a few minutes to an hour. Antihistamines are also commonly used to prevent nausea and vomiting, especially when those symptoms are due to motion sickness. This type of medication may also work at the vomiting center in the brain. Anticholinergics Anticholinergic drugs--for example, dicyclomine--slow the action of the bowel and reduce the amount of stomach acid. Because these drugs slow the action of the bowel by relaxing the muscles and relieving spasms, they are said to have an antispasmodic action. Antiulcer Medications Antiulcer medications are prescribed to relieve symptoms and promote healing of peptic ulcers. The antisecretory ulcer medications cimetidine, famotidine, and ranitidine work by suppressing the production of excess stomach acid. Another antiulcer drug, sucralfate, works by forming a chemical barrier over an exposed ulcer (like a bandage) thereby protecting the ulcer from stomach acid. These drugs provide sustained relief from ulcer pain and promote healing. Antidiarrheals Diarrhea may be caused by many conditions, including influenza and ulcerative colitis, and can sometimes occur as a side effect of drug therapy. Narcotics and anticholinergics slow the action of the bowel and can thereby help alleviate diarrhea. A medication such as diphenoxylate and atropine contains both a narcotic and an anticholinergic. HORMONES A hormone is a substance produced and secreted by a gland. Hormones stimulate and regulate body functions. Hormone drugs are given to mimic the effects of naturally produced hormones. Hormone drugs are prescribed to treat various conditions. Most often, they are used to replace naturally occuring hormones that are not being produced in amounts sufficient to regulate specific body functions. This category of medication also includes oral contraceptives and certain types of drugs that are used to combat inflammatory reactions. Thyroid Drugs Thyroid hormone was one of the first hormone drugs to be produced synthetically. Originally, thyroid preparations were made by drying and pulverizing the thyroid glands of animals and then forming them into tablets. Such preparations are still used today in the treatment of patients who have reduced levels of thyroid hormone production. However, a synthetic thyroid hormone (levothyroxine) is also available. Antidiabetic Drugs Insulin, which is secreted by the pancreas, regulates the level of glucose (a form of sugar) in the blood, as well as the metabolism of carbohydrates and fats. Insulin's counterpart, glucagon, stimulates the liver to release stored glucose. Both insulin and glucagon must be present in the right amounts to maintain the proper blood sugar levels. Treatment of diabetes mellitus (the condition in which the body is unable to produce and/or utilize insulin) may involve an adjustment of diet and/or the administration of insulin or oral antidiabetic drugs. Glucagon is given only in emergencies (for example, insulin shock, when blood sugar levels must be raised quickly). Oral antidiabetic medications induce the pancreas to secrete more insulin by acting on small groups of cells within the pancreas that make and store insulin. Oral antidiabetic medications are prescribed for diabetic patients who are unable to regulate their blood sugar levels through diet modification alone. These medications cannot be used by patients who have insulin-dependent (juvenile-onset, or Type I) diabetes; their blood sugar levels can be controlled only with injections of insulin. Steroids The pituitary gland secretes adrenocorticotropic hormone (ACTH), which directs the adrenal glands to produce adrenocorticosteroids (for example, cortisone). Oral steroid preparations (for example, prednisone) may be used to treat inflammatory diseases such as arthritis or to treat poison ivy, hay fever, or insect bites. How these drugs relieve inflammation is currently unknown. Steroids may also be applied to the skin to treat certain inflammatory skin conditions. Triamcinolone and the combination of fluocinonide, hydrocortisone, and iodochlorhydroxyquin are examples of steroid hormone creams or ointments. ---------------- The material contained here is "FOR INFORMATION ONLY" and should not replace the counsel and advice of your personal physician. Promptly consulting your doctor is the best path to a quick and successful resolution of any medical problem.