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Antimicrobial drugs, which traditionally include antibacterials, antifungals, and antivirals, work by killing or inhibiting the growth of specific microorganisms. In the past 100 years, these agents have successfully treated infectious diseases that had previously been considered incurable. Antimicrobial drugs selectively target aspects of bacterial cell wall synthesis (see Chapter 43), bacterial ribosomes (see Chapters 44 and 45), nucleotide synthesis and DNA replication (see Chapter 46), fungal cell wall synthesis (see Chapter 48), and viral replication (see Chapter 49). Combinations of these approaches are often necessary, as is seen in the treatments for mycobacterial infections (see Chapter 47).

The emergence of microbial resistance poses a constant challenge to the use of antimicrobial drugs. The selective pressure of effective drugs causes emergence of organisms that are resistant to many of the drugs in use. Mechanisms underlying microbial resistance include the production of antibiotic-inactivating enzymes, changes in the structure of target receptors, increased efflux via drug transporters, and decreases in the permeability of microbes’ cellular membranes to antibiotics. Strategies designed to combat microbial resistance include the use of adjunctive agents that can protect against antibiotic inactivation, the use of antibiotic combinations, the introduction of new (and often expensive) chemical derivatives of established antibiotics, and efforts to avoid misuse of antibiotics.

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