McKenna's Pharmacology for Nursing, 2e

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P A R T 2  Chemotherapeutic agents

Cytoplasm

Capsule

Plasma membrane

Cell wall

Cephalosporins

FIGURE 9.1  Sites of cellular action of aminoglycosides, cephalosporins, fluoroquinolones and macrolides. Aminoglycosides disrupt the cell membrane. Cephalosporins cause bacteria to build weak cell walls when dividing. Fluoroquinolones interfere with the DNA enzymes needed for growth and reproduction. Macrolides change protein function by binding to the cell membrane to cause cell death or prevent cell division.

Bacterial Flagellum

Pili

Aminoglycosides

Plasmid

Ribosomes

Nucleoid (circular DNA)

Fluroquinolones

Macrolides

Cytoplasm

Capsule

Plasma membrane

Cell wall

Penicillins

Antimycobacteria

Bacterial Flagellum

Sulfonamides

Pili

Aztreonams

Plasmid

Ribosomes

Nucleoid (circular DNA)

Carbapenems, lincosamides and ketolides

Tetracyclines

Fluroquinolones

FIGURE 9.2  Sites of cellular action of carbapenems, lincosamides, aztreonams, penicillins, sulfonamides, tetracyclines and antimycobacterials. Carbapenems and lincosamides change protein function and prevent cell division or cause cell death. Aztreonam alters cell membranes to allow leakage of intracellular substances and causes cell death. Penicillins prevent bacteria from building their cells during division. Sulfonamides inhibit folic acid synthesis for RNA and DNA production. Tetracyclines inhibit protein synthesis, thereby preventing reproduction. Antimycobacterial drugs affect mycobacteria in three ways: They (1) affect the mycotic coat of the bacteria, (2) alter DNA and RNA and (3) prevent cell division.

survival, whereas anaerobic bacteria (e.g. those bacteria associated with gangrene) do not use oxygen. If culture and sensitivity testing is not possible, either because the source of the infection is not iden- tifiable or because the person is too sick to wait for test results to determine the best treatment, clinicians attempt to administer a drug with a broad spectrum of activity against gram-positive or gram-negative bacteria or against anaerobic bacteria. Antibiotics that interfere with a biochemical reaction common to many organ- isms are known as broad-spectrum antibiotics. These drugs are often given at the beginning of treatment until the exact organism and sensitivity can be established.

Because these antibiotics have such a wide range of effects, they are frequently associated with adverse effects. Human cells have many of the same properties as bacterial cells and can be affected in much the same way, so damage may occur to the human cells, as well as to the bacterial cells. Because there is no perfect antibiotic which is without effect on the human host, clinicians try to select an antibiotic with selective toxicity, or the ability to strike foreign cells with little or no effect on human cells. Certain antibiotics may be contraindicated in some people because of known adverse effects; this includes those people who are immunocompromised,