31. Cell Wall Inhibitors
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Cell Wall Inhibitors
Some antimicrobial drugs selectively interfere with synthesis of the bacterial cell wall—a structure that mammalian cells do not possess. The cell wall is composed of a polymer called peptidoglycan that consists of glycan units joined to each other by peptide cross-links. To be maximally effective, inhibitors of cell wall synthesis require actively proliferating microorganisms; they have little or no effect on bacteria that are not growing and dividing. The most important members of this group of drugs are the β-lactam antibiotics (named after the β-lactam ring that is essential to their activity) and vancomycin. Figure 31.1 shows the classification of agents affecting cell wall synthesis.
Figure 31.1 Summary of antimicrobial agents affecting cell wall synthesis. *Cilastatin is not an antibiotic but a peptidase inhibitor that protects imipenem from degradation.
The penicillins are among the most widely effective antibiotics and also the least toxic drugs known, but increased resistance has limited their use. Members of this family differ from one another in the R substituent attached to the 6-aminopenicillanic acid residue (Figure 31.2). The nature of this side chain affects the antimicrobial spectrum, stability to stomach acid, and susceptibility to bacterial degradative enzymes (β-lactamases).
Figure 31.2 Structural features of β-lactam antibiotics.
A. Mechanism of action
The penicillins interfere with the last step of bacterial cell wall synthesis (transpeptidation or cross-linkage1), resulting in exposure of the osmotically less stable membrane. Cell lysis can then occur, either through osmotic pressure or through the activation of autolysins. These drugs are thus bactericidal. The success of a penicillin antibiotic in causing cell death is related to the antibiotic's size, charge, and hydrophobicity. Penicillins are only effective against rapidly growing organisms that synthesize a peptidoglycan cell wall. Consequently, they are inactiv
- Front Matter
- I. Introduction to Pharmacology
- II. Drugs Affecting the Autonomic Nervous System
- III. Drugs Affecting the Central Nervous System
- IV. Drugs Affecting the Cardiovascular System
- V. Drugs Affecting the Endocrine System
- VI. Drugs Affecting Other Organs
- VII. Chemotherapeutic Drugs
- 30. Principles of Anti-microbial Therapy
- 31. Cell Wall Inhibitors
- 32. Protein Synthesis Inhibitors
- 33. Quinolones, Folic Acid Antagonists & Urinary Tract Antiseptics
- 34. Antimycobacterials
- 35. Antifungal Drugs
- 36. Antiprotozoal Drugs
- 37. Anthelmintic Drugs
- 38. Antiviral Drugs
- 39. Anticancer Drugs
- 40. Immunosuppressants
- VIII. Anti-inflammatory Drugs & Autacoids