The definition of a drug is any chemical substance that has an effect on living tissue but is not used as a food. Drugs are administered to humans or animals as an aid in the diagnosis, treatment, or prevention of disease or other abnormal condition; for the relief of pain or suffering; and to control or improve any physiologic or pathologic condition. Drugs are classified according to set criteria and fall into three specific areas: general, chemical, and therapeutic.

General-Drugs are grouped according to their source, whether animal, vegetable, or mineral in origin.
Chemical-Drugs are grouped by their chemical characteristics.

Therapeutic (Pharmacological)-Drugs are grouped according to their action on the body.
NOTE: Some drugs may have more than one action.

Drug Nomenclature
Drugs normally have three names: chemical, generic, and trade (brand).

Chemical name relates to the chemical and molecular structure. An example is 2,4,7-triamino-6-phenylpteridine.
Generic name is often derived from the chemical name. Generic name is the common name of the drug. An example is triamterene. (Note the underlining of the chemical name above.)

Trade name is the proprietary name given by the manufacturer. Trade name is referred to as the brand name. An example is Dyrenium(r), a brand of triamterene made by SmithKline Beecham.

Drug Groups
The types of drugs discussed in this chapter and the correlating drugs in common use described in appendix IV are grouped according to pharmacological classes. Only a brief summary is possible here, and the Corpsman who desires a more complete description of each drug should refer to the USP-NF, Drug Facts and Comparisons, the Physicians' Desk Reference, or other drug reference books.

ASTRINGENTS.-Astringents are drugs that cause shrinkage of the skin and mucous membranes. Astringents are mainly used to stop seepage, weeping, or discharge from mucous membranes. (See appendix IV, page 1.)

EMOLLIENTS.-Emollients are bland or fatty substances that may be applied to the skin to make it more pliable and soft. They may also serve as vehicles for application of other medicinal substances. Emollients are available as ointments, creams, or lotions. (See appendix IV, page 1.)

EXPECTORANTS AND ANTITUSSIVES.- Expectorants and antitussives are commonly used in the symptomatic treatment of the common cold or bronchitis. (See appendix IV, page 1.) Expectorants are more accurately known as bronchomucotropic agents. These agents assist in the removal of secretions or exudate from the trachea, bronchi, or lungs. They act by liquefying viscid mucous or mucopurulent exudates. Therefore, they are used in the treatment of coughs to help expel these exudates and secretions. Antitussives are agents that inhibit or suppress the act of coughing. Other cold and allergy relief preparations are discussed later in this chapter.

NASAL DECONGESTANTS.-Nasal decon- gestants reduce congestion and the swelling of mucous membranes. They are used for the temporary relief of nasal congestion due to the common cold, nasal congestion associated with sinusitis, and to promote nasal or sinus drainage. Nasal decongestants are also used to relieve eustachian tube congestion. Nasal decongestants are often combined with antihistamines, antitussives, and expectorants to relieve the symptoms of colds, allergies, and sinusitis. Some of the more frequently used drug combinations are covered in appendix IV, page 2.

ANTIHISTAMINES.-Antihistamines are used to counteract the physical symptoms that histamines cause. Histamine, a substance released by mast cells distributed in connective tissues usually near blood vessels, promotes some of the reactions associated with inflammation and allergies, such as asthma and hay fever. Antihistamines may cause drowsiness, so patients should be warned against driving or operating machinery while taking this type of medication. (See appendix IV, page 2.)

HISTAMINE H2 RECEPTOR ANTAGONISTS.- Histamine H2 receptor antagonists block histamines that cause an increase of gastric acid secretion in the stomach. Histamine H2 receptor antagonists are effective in preventing complications of peptic ulcer disease and alleviating symptoms of this disease. (See appendix IV, page 2.)

ANTACIDS.-Antacids are drugs used to counteract hyperacidity in the stomach. Normally, there is a certain degree of acidity in the stomach. An excess of acid can irritate the mucous membranes and is commonly known as indigestion, heartburn, or dyspepsia. In some disease states, the gastrointestinal tract may become excessively acidic (very low pH), causing diarrhea or leading to peptic ulcer formation. Antacids may interfere with the body's ability to use many drugs. For this reason, oral drugs normally should not be taken within 2 hours of taking an antacid. (See appendix IV, page 3.)

NOTE: It is important for you to be aware of the significance of the sodium content of most antacids, particularly for cardiac patients or patients on a low-sodium diet.

ANTISEPTICS, DISINFECTANTS, AND GERMICIDES.-These agents are primarily intended for the prevention of infections by destroying bacteria or preventing their growth. The differences among them are based primarily on degree of activity and how they are used. Antiseptics suppress the growth of microorganisms. Germicides kill susceptible organisms. Disinfectants are agents used to disinfect inanimate objects and are primarily germicidal in their action. All of these agents are for external use only, unless otherwise indicated. (See appendix IV, pages 3 and 4.)

SULFONAMIDES.-Sulfonamides were the first effective chemotherapeutic agents to be available in safe therapeutic dosage ranges. They were the mainstay of therapy of bacterial infections in humans before the introduction of the penicillins in 1941. Sulfonamides are synthetically produced and are effective against both gram-positive and gram-negative organisms. (See appendix IV, page 5.)

PENICILLINS.-Penicillin is one of the most important antibiotics. It is derived from a number of Penicillium molds commonly found on breads and fruits. The mechanisms of action for the penicillins is the inhibition of cell wall synthesis during the reproductive phase of bacterial growth. It is one of the most effective and least toxic of the antimicrobial agents. (See appendix IV, page 5.)

CEPHALOSPORINS.-The cephalosporins are a group of semisynthetic derivatives of cephalosporin C, an antimicrobial agent of fungal origin. They are structurally and pharmacologically related to the penicillins. Because the cephalosporins are structurally similar to the penicillins, some patients allergic to penicillin may also be allergic to cephalo- sporin drugs. The incidence of cross-sensitivity is estimated to be 5 to 16 percent.

This family of antibiotics is generally divided into generations:

First generation - cefazolin sodium (Ancef(r), Kefzol(r))

Second generation - cefoxitin sodium (Mefoxin(r))
Third generation - cefotaxime sodium (Claforan(r))
The main differences among the groups is the change in the antibacterial spectrum. The third generation agents have a much broader gram-negative spectrum than the earlier generations.

Examples of various cephalosporins are listed in appendix IV, page 6.