What are the most commonly used antibiotics (ABX) for bacterial infections?

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Most Commonly Used Antibiotics for Bacterial Infections

The most commonly used antibiotics for bacterial infections include amoxicillin-clavulanate, fluoroquinolones (ciprofloxacin, levofloxacin), cephalosporins (cefazolin, ceftriaxone), penicillins, clindamycin, vancomycin, and doxycycline, with selection based on infection type, suspected pathogens, and resistance patterns. 1

First-Line Antibiotics by Infection Type

Skin and Soft Tissue Infections

  • Impetigo: Oral dicloxacillin, cefalexin, erythromycin, clindamycin, and amoxicillin-clavulanate 1
  • Purulent skin infections (likely Staphylococcus aureus): (Dicl)oxacillin, cefazolin, clindamycin, cefalexin, doxycycline, and sulfamethoxazole-trimethoprim 1
  • MRSA infections: Vancomycin, linezolid, clindamycin, daptomycin, ceftaroline, doxycycline, and sulfamethoxazole-trimethoprim 1
  • Non-purulent skin infections: Benzylpenicillin or phenoxymethylpenicillin, clindamycin, nafcillin, cefazolin, or cefalexin 1
  • Animal bites: Amoxicillin-clavulanate (oral); ampicillin-sulbactam, piperacillin-tazobactam, second/third-generation cephalosporins (intravenous) 1

Respiratory Infections

  • Community-acquired pneumonia: Minimum 5-day course of antibiotics covering common pathogens (S. pneumoniae, H. influenzae, M. pneumoniae, S. aureus) 1
    • Healthy adults: Amoxicillin, doxycycline, or a macrolide 1
    • Adults with comorbidities: β-lactam with a macrolide or a respiratory fluoroquinolone 1
  • COPD exacerbations: 5-day course when bacterial infection is suspected (increased sputum purulence plus increased dyspnea/sputum volume) 1
    • Options include aminopenicillin with clavulanic acid, macrolide, or tetracycline 1

Specific Pathogens

  • Streptococcus: Penicillin plus clindamycin 1
  • Staphylococcus aureus (methicillin-sensitive): Nafcillin, oxacillin, cefazolin, vancomycin, clindamycin 1
  • Clostridium species: Clindamycin plus penicillin 1
  • Pseudomonas aeruginosa: Piperacillin-tazobactam, ceftazidime, cefepime, aztreonam, and carbapenems 1

Antibiotic Classes and Their Common Uses

β-Lactams

  • Penicillins (amoxicillin, ampicillin): First-line for many common infections 1
  • Penicillinase-resistant penicillins (flucloxacillin, dicloxacillin): Antibiotics of choice for serious MSSA infections 2
  • Combination with β-lactamase inhibitors (amoxicillin-clavulanate): Broader spectrum including β-lactamase-producing organisms 3
  • Cephalosporins: Categorized by generations with varying spectrums of activity 1
    • First-generation (cefazolin, cephalexin): Good activity against staphylococci and streptococci 1
    • Second-generation (cefuroxime): Good activity against P. multocida 1
    • Third-generation (ceftriaxone, cefotaxime): Broader gram-negative coverage 1

Fluoroquinolones

  • Inhibit DNA gyrase enzyme, effective against most gram-negative pathogens 4
  • Examples: ciprofloxacin, levofloxacin, moxifloxacin 1
  • Used for respiratory, urinary tract, and gastrointestinal infections 1
  • Caution in children due to potential effects on weight-bearing joints 4

Other Important Classes

  • Macrolides/Azalides: Effective against atypical pathogens like Mycoplasma 1
  • Clindamycin: Good coverage of anaerobes and gram-positive cocci 1
  • Vancomycin: Treatment of choice for serious MRSA infections 2
  • Tetracyclines (doxycycline): Broad spectrum including some atypical pathogens 1
  • Metronidazole: Excellent anaerobic coverage 1

Considerations for Antibiotic Selection

Resistance Patterns

  • Increasing resistance is a significant concern affecting antibiotic choice 5
  • Most S. aureus strains are now resistant to penicillin 2
  • MRSA requires specific antibiotic choices (vancomycin, linezolid, etc.) 2
  • Fluoroquinolone resistance can develop, particularly in Pseudomonas aeruginosa 4

Patient Factors

  • Penicillin allergy requires alternative selections (cephalosporins may be contraindicated in immediate hypersensitivity) 2
  • Renal function may affect dosing of many antibiotics 6
  • Age considerations (fluoroquinolones generally avoided in children) 1

Duration of Therapy

  • Shorter courses (5 days) are often sufficient for common infections like pneumonia and COPD exacerbations 1
  • Extension of therapy should be based on clinical response rather than defaulting to longer courses 1

Proper Use of Antibiotics

  • Should only be used to treat bacterial infections, not viral infections 3
  • Complete the full course of therapy to prevent resistance development 3
  • Monitor for side effects, particularly diarrhea which may indicate C. difficile infection 3
  • Consider local resistance patterns when selecting empiric therapy 1

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

5
Research

Antibiotic use: present and future.

The new microbiologica, 2007

6
Research

Advances in antibiotic measurement.

Advances in clinical chemistry, 2012

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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