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21.3 Mechanisms of Action of Antibacterial Drugs S13

Table 21.2 Characteristics of Antibacterial Drugs

Target/Drug

Comments/Characteristics

Cell Wall Synthesis

ß-lactam drugs

Penicillins

Natural penicillins: penicillin G, penicillin V

Penicillinase-resistant: methicillin, dicloxicillin

Broad-spectrum: ampicillin, amoxicillin

Extended-spectrum: ticarcillin, piperacillin

Cephalosporins

Cephalexin, cephradine, cefaclor, cefprozil, cefixime, cefibuten, cefepime

Carbapenems

Imipenem, meropenem

Monobactams

Aztreonam

Vancomycin

Bacitracin

Protein Synthesis

Aminoglycosides

Streptomycin, gentamicin, tobramycin, amikacin, neomycin

Tetracyclines

Tetracycline, doxycycline

Macrolides

Erythromycin, clarithromycin, azithromycin

Chloramphenicol

Lincosamides Lincomycin, clindamycin

Oxazolidinones

Linezolid Streptogramins Quinupristin, dalfopristin

Bactericidal against a variety of bacteria; inhibits penicillin-binding proteins. Resistance is due to synthesis of ß-lactamases, decreased affinity of penicillin-binding proteins, or decreased uptake.

A family of antimicrobial medications; different groups vary in their spectrum of activity and their susceptibility to ß-lactamases. Some must be injected, but others can be taken orally.

Active against Gram-positive organisms and some Gram-negative cocci. Penicillin G is destroyed by stomach acid, and so it usually must be administered by injection. Penicillin V can be taken orally.

Similar to natural penicillins, but resistant to inactivation by the penicillinase of staphylococci. Similar to the natural penicillins, but more active against Gram-negative organisms. Increased activity against Gram-negative rods, including Pseudomonas species.

Some cephalosporins can be taken orally; others must be injected because of their instability in stomach acid.The later generations are generally more effective against Gram-negative bacteria and less susceptible to destruction by ß-lactamases.

Resistant to inactivation by b-lactamases. Imipenem must be given in combination with a drug that inhibits certain kidney enzymes in order to avoid its inactivation.

Resistant to b-lactamases; can be given to patients who are allergic to penicillin. Primarily active against members of the family

Enterobaderiaceae.

Bactericidal against Gram-positive bacteria; binds to the peptide side chain of W-acetylmuramic acid. Used to treat serious systemic infections and antibiotic-associated colitis. In enterococci, resistance is due to a plasmid-encoded altered target.

Bactericidal against Gram-positive bacteria; interferes with the transport of peptidoglycan precursors. Common ingredient in non-prescription antibiotic ointments.

Bactericidal against aerobic and facultative bacteria; binds to the 30S ribosomal subunit, blocking the initiation of translation and causing the misreading of mRNA.Toxicity limits the use. Resistance is due to a plasmid-encoded inactivating enzyme, alteration of the target molecule, or decreased uptake by a cell. Neomycin is commonly used in non-prescription topical antibiotic ointments

Bacteriostatic against some Gram-positive and Gram-negative bacteria; binds to the 30S ribosomal subunit, blocking the attachment of tRNA. Resistance is generally due to decreased accumulation, either through decreased uptake or increased efflux.

Bacteriostatic against many Gram-positive organisms as well as the most common causes of atypical pneumonia; binds to the 50S ribosomal subunit, preventing the continuation of protein synthesis. Used for treating patients who are allergic to b-lactam drugs. Resistance is due to an inactivating enzyme, alteration of the target molecule, or decreased uptake by a cell.

Bacteriostatic and broad-spectrum; binds to the 50S ribosomal subunit, preventing peptide bonds from being formed. Generally used only as a last resort for life-threatening infections. Resistance is often due to a plasmid-encoded inactivating enzyme.

Bacteriostatic against a variety of Gram-positive and Gram-negative bacteria, including the anaerobe Bacteroides fragilis; binds to the 50S ribosomal subunit, preventing the continuation of protein synthesis. Associated with an even greater risk of developing antibiotic-associated colitis.

A new class of bacteriostatic broad-spectrum drugs; binds to the 50S ribosomal subunit, interfering with the initiation of protein synthesis. Effective against a variety of Gram-positive bacteria.

A synergistic combination was recently introduced; the two drugs bind to two different sites on the 50S ribosomal subunit, inhibiting distinct steps of protein synthesis. Effective against a variety of Gram-positive bacteria.

(continued)

Chapter 21 Antimicrobial Medications

Table 21.2 (continued)

Target/Drug

Comments/Characteristics

Nucleic Acid Synthesis

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