Antimicrobial Agents Overview

• Defined as substances that inhibit microbial growth

• Essential in treating infections caused by bacteria and other microorganisms.

Objectives

• Assess the need for antimicrobial agents.

• Describe therapeutic indications for their use.

• Prioritize the prescribing of appropriate agents based on clinical scenarios.

Factors in Selecting Antimicrobial Agents

• Systemic Approach: Thorough assessment to identify the source of infection.

• Setting of Infection: Consider the location and context of the infection.

Patient Assessment Components

• Conduct a Physical Exam.

• Evaluate Chief Complaint and Present Illness.

• Note any Recent Travel and Past History.

• Identify the Source of the infection.

• Perform necessary Lab Tests.

• Recognize when body and immune defenses have failed leading to a 'sick' patient.

Diagnostic Methods for Infection

1. Direct Microscopic Visualization

2. Culture and Identification: Culturing the pathogen to determine the infectious organism.

3. Detection of Microbial Antigens: Identifying specific microbial markers in the body.

4. Detection of Microbial RNA or DNA: Utilizing molecular methods for pathogen identification.

5. Host Immune Response Detection: Understanding how the host's immune system is responding to the pathogen.

Bacteria Classification

• Gram-Negative Bacteria:

  • Characterized by an outer membrane containing lipopolysaccharides.

• Gram-Positive Bacteria:

  • Composed of thick peptidoglycan layers without an outer membrane.

Antibiotics Classification

• Broad Spectrum: Effective against a wide range of bacteria.

• Narrow Spectrum: Target specific types of bacteria.

• Bactericidal: Kill bacteria.

• Bacteriostatic: Inhibit bacterial growth without killing them.

• Common tests include Kirby-Bauer Antibiotic Sensitivity Test and Minimum Inhibitory/Bactericidal Concentration Tests.

Mechanisms of Action for Antibiotics

• Inhibition of Cell Wall Synthesis: Prevents bacteria from forming cell walls.

• Inhibition of Nucleic Acid Synthesis: Interferes with the replication or transcription of bacterial DNA.

• Disruption of Cell Membrane Integrity: Alters the membrane structure, leading to cell death.

• Inhibition of Protein Synthesis: Disrupts translating processes, affecting bacterial growth.

• Inhibition of Metabolic Pathways: Block necessary biochemical pathways for bacterial survival.

Antibiotic Resistance

• Causes: Bacterial production of enzymes (e.g., penicillinase) that neutralize antibiotics.

• Mechanisms: Includes the destruction of the antibiotic (e.g., breaking the beta-lactam ring) or inhibiting its action.

• β-lactam/β-lactamase Inhibitors: Agents like clavulanic acid enhance antibiotic efficacy against resistant strains.

Penicillins Overview

• Classified by Spectrum of Activity: Natural, resistant, aminopenicillins, and extended spectrum.

• Mechanism of Action: Inhibit bacterial cell wall synthesis.

• Common Uses: Effective against various infections including respiratory and soft tissue infections.

• Adverse Events: Mostly hypersensitivity reactions; can cause seizures in cases of severe renal dysfunction.

Cephalosporins Overview

• Pharmacokinetics: Well absorbed; good penetration into tissues; primarily renal excretion.

• Cross-sensitivity with Penicillins: Possible (3%-10%) if patients have significant allergies to penicillin.

• Uses: Versatile use in treating various infections with a favorable toxicity profile.

Fluoroquinolones Overview

• Mechanism of Action: Concentration-dependent killing effect.

• Absorption and Distribution: Good tissue penetration with renal elimination.

• Adverse Effects: Risk of tendon rupture, QTc prolongation, and neuropathy.

Macrolides Overview

• Examples: Erythromycin, Azithromycin, Clarithromycin.

• Uses: Commonly prescribed for respiratory tract infections and STDs; good tissue penetration.

• Adverse Effects: GI distress, potential drug interactions with CYP450 inhibitors.

Tetracyclines Overview

• Broad Spectrum Activity: Effective against a variety of bacteria including gram-positive, gram-negative, and atypical organisms.

• Adverse Effects: Photosensitivity, potential effects on bone and tooth development in children (discoloration).

Aminoglycosides Overview

• Administration: Primarily parenteral due to poor GI absorption.

• Uses: Effective against systemic infections, particularly gram-negative bacteria.

• Adverse Effects: Nephrotoxicity and ototoxicity.

Miscellaneous Antibiotics Overview

• Daptomycin: Effective against resistant gram-positive infections.

• Metronidazole: Used for anaerobic infections and C. difficile colitis.

• Clindamycin: Broadly effective for gram-positive and anaerobic coverage, often associated with C. difficile risk.

Patient Education & Proper Use of Antibiotics

• Importance of completing prescribed courses of antibiotics.

• Advising against self-discontinuation of antibiotics without medical guidance.

• Education on potential side effects and proper administration practices.