Lecture Notes: Introduction to Antibiotics

Introduction

• Topic: Pharmacodynamics session on antibiotics
• Early lecture to provide exposure to antibiotics before Farm One in Fall
• Importance: Antibiotics are crucial in various medical fields

Instructional Objectives

• Review of Microbiology: To understand antibiotic terminology and classification
• Patient Infections: Identify infection sites and types of bacteria

Bacterial Classification

• Gram Positive vs. Gram Negative: Crucial for antibiotic selection
  • Examples: Gram-positive cocci in clusters (e.g., Staph aureus) vs. gram-negative bacilli
• Spectrum of Antibiotics: Narrow vs. broad spectrum based on bacteria treated

Types of Bacteria

• Gram-Positive Bacteria
  • Staph aureus (MSSA vs. MRSA)
  • Strep pneumoniae
  • Enterococcus (in GI tract)
• Gram-Negative Bacteria
  • Common in urinary tract infections
  • Examples: E. coli, Proteus, Salmonella
  • Pseudomonas aeruginosa (resistant hospital-acquired infections)
  • Haemophilus influenzae (upper respiratory infections)
  • Neisseria gonorrhoeae
• Anaerobic Bacteria
  • Examples: Clostridium difficile (C. diff)
  • Oral anaerobes (e.g., Peptostreptococcus)

Infection Sites and Bacteria

• Skin and Soft Tissue Infections: Mostly gram-positive bacteria
• Bone and Joint Infections: Mainly gram-positive; some gram-negative (decubitus ulcers)
• Meningitis: Based on patient age and immune status
• Abdominal Infections: Both gram-negative and anaerobes
• UTIs: Primarily gram-negative, but can include gram-positive (e.g., catheters)
• Mouth Infections: Anaerobes due to oral flora
• Respiratory Tract Infections: Community-acquired vs. nosocomial (hospital-acquired)

Determining Antibiotic Effectiveness

• Antibiogram: Local resistance patterns to guide drug selection
• Cultures and Sensitivities: Test bacterial growth against various antibiotics
  • Zone of Inhibition: Area where bacteria don't grow, showing effectiveness
  • MIC (Minimum Inhibitory Concentration): Lowest concentration that inhibits bacterial growth

Controlling Resistance

• Judicious Antibiotic Use: Avoid unnecessary use to prevent resistance
• Antimicrobial Stewardship: Hospital programs to optimize antibiotic use

Antibiotic Mechanisms and Categories

• Cell Wall Inhibitors: Beta-lactam antibiotics (e.g., penicillins, cephalosporins)
  • Disrupt cell wall synthesis, bactericidal
  • Time-dependent killers (require frequent dosing)
• Protein Synthesis Inhibitors: Target bacterial ribosomes (e.g., aminoglycosides, tetracyclines)
  • Different ribosomal subunits in bacteria vs. humans
• DNA and RNA Synthesis Inhibitors: Inhibit enzymes involved in DNA replication (e.g., fluoroquinolones)
• Drug Examples and Their Uses:
  • Penicillins: Treat various infections, some specific to MRSA or MSSA
  • Cephalosporins: Generational differences in spectrum (e.g., 3rd gen for broad spectrum)
  • Vancomycin: MRSA infections, C. diff (oral form)
  • Macrolides (e.g., azithromycin): Respiratory tract infections, atypical bacteria
  • Clindamycin: Anaerobic and gram-positive infections, risk for C. diff
  • Fluoroquinolones: Broadspectrum, respiratory and urinary infections
  • Metronidazole: Anaerobic infections (e.g., C. diff), avoid alcohol (disulfiram-like reaction)

Considerations and Side Effects

• Allergies: Document and verify true allergic reactions
• Side Effects: Common GI issues, photosensitivity, potential toxicity (e.g., nephrotoxicity with vancomycin)
• Special Instructions
  • Tetracyclines: Avoid dairy and antacids
  • Fluoroquinolones: Risk of tendonitis, QT prolongation
  • Metronidazole: Avoid alcohol due to disulfiram reaction

Exam Preparation

• Focus Areas: Identify antibiotic classes, mechanisms of action, unique side effects
• Question Types: Likely to include drug class identification and matching bugs to antibiotics

Final Notes

• Review of key antibiotic classes and mechanisms
• Emphasis on empiric vs. targeted therapy based on cultures and sensitivity results