Antibiotics

Drugs for Treating Infections

Terminology

• Antimicrobial

  • Definition: Any drug used to treat infections caused by microorganisms.

  • Subcategories:

  • Antibacterial: Targets bacteria specifically.

  • Antifungals: Targets fungi.

  • Antivirals: Targets viruses.

Microorganisms

• Prokaryote

  • Characteristics:

  • Simple structure, lacking a nucleus (no defined cell structure).

  • Example: Bacteria.

• Eukaryote

  • Characteristics:

  • Complex cell with a membrane-bound nucleus.

  • Examples: Fungi and human cells.

Classification of Antibiotics

• Based on susceptible organisms:

  • Narrow Spectrum: Effective against a limited range of organisms.

  • Broad Spectrum: Effective against a wide variety of bacteria but may not be as efficient for specific infections.

Historical Background

• Louis Pasteur was a pioneer in microbiology, credited with the discovery of bacteria.

Selection of Antimicrobial

• Factors influencing selection:

  • Identity of microorganism: Exact type or probable type of the infectious agent.

  • Site of infection: Location of the infection in the body.

  • Patient-specific factors:

  • Immune system status.

  • Overall health status including conditions like diabetes.

  • Age of the patient.

  • Pregnancy and lactation status.

  • History of allergies.

Bacterial Classification

• Gram-positive (+):

  • Characteristics:

  • Thick, rigid peptidoglycan layer.

  • Smaller periplasmic space.

  • Absorbs crystal violet stain, appearing purple under a microscope.

• Gram-negative (-):

  • Characteristics:

  • Thinner peptidoglycan layer surrounded by an outer lipopolysaccharide membrane.

  • Appears pink after gram staining due to the absence of crystal violet retention.

Classification of Antibiotics (by Action)

• Bactericidal

  • Definition: Antibiotics that kill bacteria.

• Bacteriostatic

  • Definition: Antibiotics that inhibit the reproduction of bacteria (similar to birth control for bacteria).

Mechanisms of Action of Antibiotics

• Cell wall synthesis inhibitors:

  • Target the bacterial cell wall's integrity, lethal to bacteria.

• Examples include:

  • Bacitracin

  • Penicillins

  • Cephalosporins

  • Macrolides

  • Tetracycline

Details on Antibiotic Classes

Beta-Lactams

• Includes: Penicillins & Cephalosporins.

• Mechanism: Inhibit bacterial cell walls, classified as bactericidal.

• Penicillins:

  • More than 200 million lives saved due to its therapeutic uses.

  • Used for various infections including:

  • Urinary Tract Infections (UTIs)

  • Respiratory Tract Infections (RTIs)

  • Otitis

  • Syphilis

  • Endocarditis

  • Effectiveness may decline if bacteria develop penicillinase (an enzyme that can deactivate penicillin).

  • Types of Penicillins:

  • Penicillin G (natural, narrow spectrum).

  • Amoxicillin (broad spectrum, resistant to penicillinase).

Cephalosporins

• B-Lactams that inhibit cell wall synthesis.

• Allergy Consideration: About 10% of individuals allergic to penicillin may also be allergic to cephalosporins (0.1%-0.2% cross-reactivity).

• Typically effective against Gram-positive and some Gram-negative bacteria.

Carbapenems

• Usage: Only parenterally (administered via injection, used in hospital settings).

• Broad spectrum antibiotic.

• Mechanism: Inhibit cell wall synthesis and are bactericidal.

Tetracyclines

• Not beta-lactams; useful for penicillin allergies.

• Mechanism: Inhibit protein synthesis, classified as bacteriostatic; they inhibit bacterial growth rather than killing directly.

• Adverse effects:

  • Should be avoided in children and pregnant women due to risks like discoloration of teeth.

  • Can cause photosensitivity (increased susceptibility to sunburn).

  • Common Examples: Doxycycline and Minocycline.

Macrolides

• Function: Inhibit protein synthesis, primarily effective against Gram-positive organisms.

• Used for outside infections like community-acquired pneumonia.

• Can cause gastrointestinal issues but are well-tolerated with food.

• Common drugs include Azithromycin (Z-Pak) and Clarithromycin (Biaxin).

Sulfonamides

• Function: Inhibit protein synthesis and involve folic acid derivatives (PABA, dihydrofolate).

• Effective against a range of infections, including burns and can be used topically.

Side Effects of Antibiotics

• Side effects vary with class but can include:

  • Renal damage.

  • Hypersensitivity reactions.

Fluoroquinolones

• Examples: Levofloxacin and Ciprofloxacin.

• Mechanism: Inhibit DNA synthesis, classified as bactericidal.

• Interactions:

  • Do not take with calcium or multivitamins (2 hours before or 30 minutes after).

  • Possible adverse reactions such as tendon damage and interaction with oral contraceptives (reduced efficacy).

Miscellaneous Antibiotics

• Clindamycin:

  • Effective for Gram-positive infections but can cause gastrointestinal side effects and C. difficile superinfections.

• Aminoglycosides:

  • Include Streptomycin, Gentamicin, and Tobramycin.

Superinfections

• Definition: Secondary infections caused by treatment of a primary infection (e.g., superinfection from C. difficile following antibiotic use).

Systemic Fungal Infections

• Types of Antifungals:

  • Work by disrupting the cell membrane of fungi, leading to cell death (bactericidal).

  • Azole Antifungals: Widespread use, generally well tolerated but may have hepatotoxic effects.

Common Fungal Infections and Treatments

• Tinea Pedis (Athlete's Foot):

  • Treatment may involve OTC topical agents and can take 2-6 weeks to resolve.

• Tinea Capitis:

  • Requires systemic therapy for complete treatment over 1-3 months.

• Tinea Cruris (Jock Itch):

  • Characterized by redness and itching in the groin area, generally treated over 1-2 weeks.

• Tinea Ungulum (Toenail Fungus):

  • Tougher to treat, often requires prescription treatment and can be expensive.

Yeast Infections

• Common Types:

  • Vaginal Candidiasis (thrush); treatment can be topical or systemic.

  • Symptoms may involve itching and discharge and are treated with antifungals.