McKenna's Pharmacology for Nursing, 2e

82 P A R T 2  Chemotherapeutic agents A nti-infective agents are drugs designed to target foreign organisms that have invaded and infected the body of a human host. For centuries, people have used various naturally occurring chemicals in an effort to treat disease. Often this was a random act that proved useful. For instance, the ancient Chinese found that applying mouldy soybean curds to boils and infected wounds helped prevent infection or hastened cure. Their finding was, perhaps, a forerunner to the penicillins used today. The use of drugs to treat systemic infections is a rela­ tively new concept, beginning with Paul Ehrlich in the 1920s. Ehrlich’s research to develop a synthetic chemical that would be effective only against infection-causing cells, not human cells, led the way for the scientific investigation of anti-infective agents. In the late 1920s, scientists discovered penicillin in a mould sample; in 1935, the sulfonamides were introduced. Since then, the number of anti-infectives available for use has grown tremendously. However, many of the organisms these drugs were designed to treat are rapidly adapting to repel the effects of anti-infectives, and, therefore, much work remains to deal with these emergent strains. ANTI-INFECTIVE AGENTS Although anti-infective agents target foreign organ- isms infecting the body of a human host, they do not possess selective toxicity , which is the ability to affect certain proteins or enzyme systems used by the infecting organism but not by human cells. Because all living cells This box presents general principles of use of anti- infectives across the lifespan. Specifics for each type of anti-infective agent are discussed in their respective chapters within this unit. Anti-infective agents CHILDREN Use anti-infectives with caution; early exposure can lead to early sensitivity. Controversy is widespread regarding the use of antibiotics to treat ear infections, a common paediatric problem. Some believe that the habitual use of antibiotics for what might well be a viral infection has contributed greatly to the development of resistant strains. Because children can have increased susceptibility to the gastrointestinal and nervous system effects of anti-infectives, monitor hydration and nutritional status BOX 8.1

are somewhat similar, however, no anti-infective drug has yet been developed that does not affect the host. This chapter focuses on the principles involved in the use of anti-infective therapy, and presents some anti- infectives as examples of these principles. The following chapters discuss specific agents used to treat particular infections: antibiotics for bacterial infections; antivirals; antifungals; antiprotozoals for infections caused by specific protozoa, including malaria; and anthelmin­ tics for infections caused by worms. The final chapter in this section discusses antineoplastics—drugs used for treating diseases caused by abnormal cells such as cancers. Antineoplastics specifically affect human cells to cause cell death or prevent cell growth and reproduc- tion. The effects of anti-infectives on various age groups are discussed in Box 8.1. Therapeutic actions Anti-infective agents may act on the cells of invading organisms in several different ways. The goal is inter- ference with the normal function of the invading organism to prevent it from reproducing and to cause cell death without affecting host cells. Various mecha- nisms of action are briefly described here and shown in Figure 8.1. The specific mechanism of action for each drug class is discussed in the chapters that follow. • Some anti-infectives interfere with biosynthesis of the bacterial cell wall. Because bacterial cells have a slightly different composition than human cells, this is an effective way to destroy the bacteria without emergence of resistant strains can be a big problem with this group. PREGNANCY AND BREASTFEEDING Women who are pregnant or breastfeeding must exercise extreme caution in the use of anti-infectives. Many anti- infectives can affect the fetus and also cross into breast milk, leading to toxic effects in the neonate. OLDER ADULTS Older people often do not present with the same signs and symptoms of infection that are seen in younger people. Culture and sensitivity tests are important to determine the type and extent of many infections. The older person is susceptible to severe adverse gastrointestinal, renal and neurological effects and must be monitored for nutritional status and hydration during drug therapy. Anti-infectives that adversely affect the liver and kidneys must be used with caution in older people, who may have decreased organ function.

Drug therapy across the lifespan

carefully. ADULTS

Adults often demand anti-infectives for a “quick cure” of various signs and symptoms. Drug allergies and the