Drug

I

Introduction

Drug, substance that affects the function of living cells, used in medicine to diagnose, cure, prevent the occurrence of diseases and disorders, and prolong the life of patients with incurable conditions.

The availability of new and more effective drugs, such as antibiotics, which fight bacterial infections, and vaccines, which prevent diseases caused by bacteria and viruses, helped increase the average American’s life span from about 60 years in 1900 to about 78 years in 2005. Drugs have vastly improved the quality of life. During the 20^th century, drugs enabled the eradication of smallpox, once a widespread and often fatal disease. By the early 21^st century, vaccines had led to the near eradication of poliomyelitis, once feared as a cause of paralysis.

II

Classification of Drugs

Drugs can be classified in many ways: by the way they are dispensed——over the counter or by prescription; by the substance from which they are derived—plant, mineral, or animal; by the form they take—capsule, liquid, or gas; and by the way they are administered—by mouth, injection, inhalation, or direct application to the skin (absorption). Drugs are also classified by their names. All drugs have three names: (1) a chemical name, which describes the exact structure of the drug; (2) a generic or proprietary name, which is the official medical name, assigned in the United States by the U.S. Adopted Name Council (a group composed of pharmacists and other scientists); and (3) a brand, or trade, name, given by the particular manufacturer that sells the drug. If a company holds the patent on a drug—that is, if the company has the exclusive right to make and sell a drug—then the drug is available under one brand name only. After the patent expires, typically after 17 years in the United States, other companies can also manufacture the drug and market it under the generic name, or give it a new brand name.

Another way to categorize drugs is by the way they act against diseases or disorders: chemotherapeutic drugs attack specific organisms that cause a disease without harming the host, while pharmocodynamic drugs alter the function of bodily systems by stimulating or depressing normal cell activity in a given system. The most common way to categorize a drug is by its effect on a particular area of the body or a particular condition.

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A

Endocrine Drugs

Endocrine drugs correct the overproduction or underproduction of the body’s natural hormones. For example, insulin is a hormone used as a drug to treat diabetes. Another example of endocrine drugs are birth control pills, which contain the female sex hormones estrogen and progesterone.

B

Drugs that Fight Infections

Anti-infective drugs are classified as antibacterials, antivirals, or antifungals depending on the type of microorganism they combat. Anti-infective drugs interfere selectively with the functioning of a microorganism while leaving the human host unharmed.

Antibacterial drugs, or antibiotics—sulfa drugs, penicillins, cephalosporins, and many others—either kill bacteria directly or prevent them from multiplying so that the body’s immune system can destroy invading bacteria. Antibacterial drugs act by interfering with some specific characteristics of bacteria. For example, they may destroy bacterial cell walls or interfere with the synthesis of bacterial proteins or deoxyribonucleic acid (DNA)—the chemical that carries the genetic material of an organism. Antibiotics often cure an infection completely. However, bacteria can spontaneously mutate, producing strains that are resistant to existing antibiotics.

Antiviral drugs interfere with the life cycle of a virus by preventing its penetration into a host cell or by blocking the synthesis of new viruses. Antiviral drugs may cure, but often only suppress, viral infections; and flare-ups of an infection can occur after symptom-free periods. With some viruses, such as human immunodeficiency virus (HIV), which causes acquired immunodeficiency syndrome (AIDS), antiviral drugs can only prolong life, not cure the disease.

Vaccines are used as antiviral drugs against diseases such like mumps, measles, smallpox, poliomyelitis, and influenza. Vaccines are made from either live, weakened viruses or killed viruses, both of which are designed to stimulate the immune system to produce antibodies, proteins that attack foreign substances. These antibodies protect the body from future infections by viruses of the same type (see Immunization).

Antifungal drugs selectively destroy fungal cells by altering cell walls. The cells’ contents leak out and the cells die. Antifungal drugs can cure, or may only suppress, a fungal infection.

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