What antibiotics cover which common bacterial infections?

Antibiotic Coverage for Common Bacterial Infections

The most appropriate antibiotics for common bacterial infections should be selected based on the suspected pathogen, with specific first-line choices for each infection type as recommended by clinical guidelines. 1

Respiratory Tract Infections

Community-Acquired Pneumonia (CAP)

• First-line therapy:
  • Healthy adults (outpatient): Amoxicillin, doxycycline, or a macrolide (azithromycin) 1, 2
  • Adults with comorbidities (outpatient): β-lactam (amoxicillin/clavulanate) plus a macrolide OR respiratory fluoroquinolone (levofloxacin, moxifloxacin) 1, 2
  • Hospitalized non-ICU patients: Ceftriaxone (1-2g daily) PLUS azithromycin (500mg daily) 2
  • ICU patients: Antipseudomonal β-lactam (cefepime, piperacillin-tazobactam) plus either a respiratory fluoroquinolone or a macrolide 2

Atypical Pathogens

• Mycoplasma pneumoniae: Doxycycline (100mg twice daily) or azithromycin (500mg day 1, then 250mg daily for 4 days) 1, 2
• Chlamydophila pneumoniae: Azithromycin, clarithromycin, doxycycline, levofloxacin, or moxifloxacin 1
• Legionella species: Levofloxacin or moxifloxacin (preferred), or azithromycin 1, 2

COPD Exacerbations

• First-line therapy: Aminopenicillin with clavulanic acid, macrolide, or tetracycline for 5 days 1
• Common pathogens: Haemophilus influenzae, Streptococcus pneumoniae, Moraxella catarrhalis 1

Skin and Soft Tissue Infections

Mild Infections (Impetigo, Cellulitis)

• First-line therapy: Amoxicillin-clavulanic acid, cloxacillin, or cefalexin 1
• MRSA suspected: Vancomycin, linezolid, clindamycin, daptomycin, or sulfamethoxazole-trimethoprim 1

Necrotizing Fasciitis

• First-line therapy: Clindamycin plus piperacillin-tazobactam (with or without vancomycin) OR ceftriaxone plus metronidazole (with or without vancomycin) 1

Diabetic Foot Infections

• Mild infections: Dicloxacillin, clindamycin, cefalexin, levofloxacin, amoxicillin-clavulanic acid, or doxycycline 1
• Moderate to severe infections: Levofloxacin, cefoxitin, ceftriaxone, ampicillin-sulbactam, moxifloxacin, ertapenem, or tigecycline 1
• MRSA suspected: Linezolid, daptomycin, or vancomycin 1

Urinary Tract Infections

Uncomplicated UTIs

• Common pathogens: Escherichia coli (most common), Klebsiella species, Proteus species
• First-line therapy: Nitrofurantoin, trimethoprim-sulfamethoxazole, fosfomycin 3

Complicated UTIs

• First-line therapy: Fluoroquinolones (ciprofloxacin, levofloxacin), third-generation cephalosporins, or aminoglycosides 3
• For resistant pathogens: Carbapenems (ertapenem, meropenem) 3

Specific Bacterial Pathogens and Their Coverage

Gram-Positive Bacteria

• Streptococcus pneumoniae:

  • Penicillin-susceptible: Penicillin G, amoxicillin, amoxicillin-clavulanate, ampicillin 1
  • Penicillin-resistant: Ceftriaxone, cefotaxime, respiratory fluoroquinolones, vancomycin, linezolid 1

• Staphylococcus aureus:

  • Methicillin-susceptible: Oxacillin, cefazolin, flucloxacillin 1
  • Methicillin-resistant: Vancomycin, teicoplanin, linezolid 1

Gram-Negative Bacteria

• Haemophilus influenzae:

  • β-lactamase negative: Amoxicillin 1
  • β-lactamase positive: Amoxicillin-clavulanate, second/third-generation cephalosporins, fluoroquinolones 1

• Pseudomonas aeruginosa: Antipseudomonal β-lactams (piperacillin-tazobactam, ceftazidime, cefepime), carbapenems, fluoroquinolones, aminoglycosides 1, 4

• Enterobacteriaceae: Third-generation cephalosporins, fluoroquinolones, aminoglycosides, carbapenems 4

Key Considerations for Antibiotic Selection

1. Local resistance patterns: Always consider local antibiogram data when selecting empiric therapy 2

2. Patient factors:

   • Drug allergies (particularly penicillin)
   • Renal/hepatic function
   • Recent antibiotic exposure (within 3 months) 2

3. Duration of therapy:

   • CAP: Minimum 5 days, with patient afebrile for 48-72 hours 1, 2
   • COPD exacerbations: 5 days 1
   • Skin infections: 5-7 days for uncomplicated infections, longer for severe infections 1

4. De-escalation: Narrow therapy once culture results are available to reduce resistance development 1

Special Considerations

• Immunocompromised patients: Broader empiric coverage is often needed, including coverage for resistant organisms 5

• Biomarkers: Procalcitonin levels >0.5 ng/mL may indicate bacterial infection; can guide antibiotic initiation and discontinuation 1

• Combination therapy: Consider for severe infections, particularly when Pseudomonas aeruginosa is suspected 1, 4

• Topical antibiotics: For conjunctivitis and otitis externa, fluoroquinolones (ciprofloxacin, ofloxacin) are effective options 1

Remember that antibiotic resistance is a growing global concern, with at least 700,000 deaths annually attributed to antimicrobial resistance. Judicious use of antibiotics with the narrowest effective spectrum for the shortest effective duration is essential to preserve antibiotic efficacy 4.