McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 8  Anti-infective agents

Cytoplasm

Capsule

Plasma membrane

Cell wall

RNA alteration

Membrane disruption

Bacterial Flagellum

Pili

Plasmid

Ribosomes

Nucleoid (circular DNA)

DNA synthesis alteration

Blocking use of needed nutrients

FIGURE 8.1  Anti-infectives can affect cells by disrupting the cell membrane interfering with DNA synthesis, altering RNA or blocking the use of essential nutrients.

interfering with the host (see Box 8.2). The penicillins work in this way. • Some anti-infectives prevent the cells of the invading organism from using substances essential to their growth and development, leading to an inability to divide and eventually to cell death. The sulfonamides, the antimycobacterial drugs and trimethoprim- sulfamethoxazole (a combination drug frequently used to treat urinary tract infections) work in this way. • Many anti-infectives interfere with the steps involved in protein synthesis, a function necessary to maintain the cell and allow for cell division. The aminoglycosides, the macrolides and chloramphenicol (see the section on adverse effects for information on chloramphenicol) work in this way. • Some anti-infectives interfere with DNA synthesis in the cell, leading to inability to divide and cell death. The fluoroquinolones work in this way. • Other anti-infectives alter the permeability of the cell membrane to allow essential cellular components to leak out, causing cell death. Some antibiotics, Teicoplanin ( Targocid ) is an antibiotic that interferes with the cell wall synthesis of susceptible staphylococcal bacteria. Adverse effects include phlebitis, bronchospasm, pruritus and fever. Because of the development of resistant strains and more potent antibiotics, teicoplanin is only indicated for serious infections that cannot be treated by other less toxic drugs, such as osteomyelitis, bacteraemia and septicaemia. It is given by intravenous or intramuscular administration. ■■ BOX 8.2  Anti-infective mechanism: Interference with cell wall synthesis

antifungals and antiprotozoal drugs work in this manner. Anti-infective activity The anti-infectives used today vary in their spectrum of activity; that is, they vary in their effectiveness against invading organisms. Some anti-infectives are so selec- tive in their action that they are effective against only a few microorganisms with a very specific metabolic pathway or enzyme. These drugs are said to have a narrow spectrum of activity. Other drugs interfere with biochemical reactions in many different kinds of micro- organisms, making them useful in the treatment of a wide variety of infections. Such drugs are said to have a broad spectrum of activity. Some anti-infectives are so active against the infec- tive microorganisms that they actually cause the death of the cells they affect. These drugs are said to be bacteri­ cidal . Some anti-infectives are not as aggressive against invading organisms; they interfere with the ability of the cells to reproduce or divide. These drugs are said to be bacteriostatic . Several drugs are both bactericidal and bacteriostatic, often depending on the concentration of the drug that is present. Many of the adverse effects noted with the use of anti-infectives are associated with the aggressive properties of the drugs and their effect on the cells of the host in addition to those of the pathogen. Human immune response The goal of anti-infective therapy is reduction of the population of the invading organism to a point at which the human immune response can take care of the infec- tion. If a drug were aggressive enough to eliminate all traces of any invading pathogen, it also might be toxic to the host. The immune response (see Chapter 15) involves a complex interaction among chemical