Chapter 14: Antimicrobial Agents Notes

Antimicrobial Agents Notes

Chapter 14 Overview

• This chapter covers various aspects of antimicrobial agents, including definitions, mechanisms, classifications, and clinical uses.

Objectives

• Define Terms Related to Antimicrobial Agents: Understanding key terms is crucial for grasping the principles of antimicrobial therapy.
• Define Antibiotic: A specific type of antimicrobial agent that kills or inhibits the growth of bacteria.
• Bacterial Susceptibility Testing: Understanding how to determine which antimicrobial agents are effective against specific bacteria.
• Antimicrobial Combinations: Recognizing how different combinations can affect treatment outcomes.

Key Classifications of Antimicrobials

• Penicillins: Class includes natural penicillins, penicillinase-resistant, aminopenicillins, carboxypenicillins, and ureidopenicillins.
• Cephalosporins: Divided into generations, each with varying effectiveness against gram-positive and gram-negative bacteria.
• Macrolides, Azalides, and Ketolides: Recognizing similarities in their structures and functions.
• Fluoroquinolones: Class known for effective DNA synthesis inhibition.
• Antimycobacterials: Specifically targeting Mycobacterium species, such as tuberculosis.
• Antifungals: Including azoles and echinocandins, among others.
• Antivirals: Cover various viral infections, showing different mechanisms of action.

Principles of Antimicrobial Therapy

• Gram Staining: Basic method to classify bacteria into Gram-positive (purple) and Gram-negative (pink).
• Culture Specimen Collection: Essential samples include blood, urine, sputum, and more for accurate identification of pathogens.
• Antimicrobial Therapy Dependence: Factors impacting therapy include host factors, pharmacodynamics, and organism susceptibility.

Susceptibility Testing Overview

• Kirby-Bauer Disk Diffusion: A method of testing antibiotic efficacy using agar plates.
• E-test: Measures Minimal Inhibitory Concentration (MIC) using strips with a gradient of antimicrobial.

Key Mechanisms of Action of Antibacterial Agents

1. Inhibition of Cell Wall Synthesis: Targeted by penicillins and cephalosporins (e.g., beta-lactams).
2. Inhibition of Protein Synthesis: Involves macrolides and aminoglycosides.
3. Inhibition of DNA/RNA Synthesis: Achieved by fluoroquinolones and rifampin.
4. Inhibition of Metabolic Pathways: Such as trimethoprim-sulfamethoxazole affecting folic acid synthesis.

Adverse Reactions and Precautions of Antimicrobials

• Penicillins: Notable for hypersensitivity and possible gastrointestinal effects.
• Cephalosporins: Risks include hypersensitivity and minor GI complaints.
• Aminoglycosides: Monitor for nephrotoxicity and ototoxicity.
• Tetracyclines: Can affect bone growth and absorb certain minerals.

Antimycobacterial Drugs

• Isoniazid: Inhibits cell wall synthesis, hepatotoxicity is a concern.
• Rifampin: Affects RNA polymerase; watch for hepatotoxicity and orange bodily fluids.
• Ethambutol: Known for optic neuropathy as a side effect.

Antifungal Overview

• Polyenes (e.g., Amphotericin B): Increase cell membrane permeability.
• Azoles: Inhibit ergosterol synthesis, useful in candidiasis treatment.
• Echinocandins: Target fungal cell wall synthesis, used for severe infections.

Antiviral Agents

• Acyclovir/Valacyclovir: Stop viral replication; used for herpes viruses.
• Neuraminidase Inhibitors (e.g., Oseltamivir): Useful for treating influenza.

Biologics and Monoclonal Antibodies

• Emerging treatments for infectious diseases and other disorders such as monoclonal antibodies targeting Bacillus anthracis (e.g., Raxibacumab).

Conclusion: Monitoring Response to Therapy

• Clinical assessments and laboratory monitoring are crucial in evaluating the efficacy of antimicrobial therapy and adjusting treatment based on the organism's response and the patient’s condition.