When and how should antibiotics, such as amoxicillin, ciprofloxacin (Cipro), or metronidazole (Flagyl), be used to treat bacterial infections?

Appropriate Use of Antibiotics for Bacterial Infections

Antibiotics should be prescribed only for confirmed or strongly suspected bacterial infections, with selection based on the specific infection type, suspected pathogens, and local resistance patterns to maximize effectiveness while minimizing resistance development. 1

General Principles of Antibiotic Use

• Antibiotics should only be used to treat bacterial infections, not viral infections like the common cold 2
• The full prescribed course of antibiotics should be completed to prevent treatment failure and development of antibiotic resistance 3, 2
• Selection of antibiotics should be based on the suspected pathogen, infection site, and local resistance patterns 1, 4
• Narrow-spectrum antibiotics should be used whenever possible to minimize disruption of normal flora and reduce selection pressure for resistant organisms 3

Specific Antibiotic Recommendations by Infection Type

Skin and Soft Tissue Infections

• Mild skin infections (impetigo, cellulitis):

  • First choice: Amoxicillin-clavulanic acid or cloxacillin 1
  • Alternative: Cephalexin, dicloxacillin, or erythromycin 1

• Purulent skin infections (likely Staphylococcus aureus):

  • First choice: Dicloxacillin, cefazolin, or cephalexin 1
  • If MRSA suspected: Trimethoprim-sulfamethoxazole, doxycycline, or clindamycin 1

• Necrotizing fasciitis:

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

• Animal bites:

  • Oral treatment: Amoxicillin-clavulanic acid 1
  • Intravenous treatment: Ampicillin-sulbactam, piperacillin-tazobactam, or second/third-generation cephalosporins 1
  • For anaerobic coverage: Add metronidazole or clindamycin if needed 1

• Human bites:

  • First choice: Amoxicillin-clavulanic acid or ampicillin-sulbactam 1
  • Alternatives: Carbapenems or doxycycline 1

Intra-abdominal Infections

• Complicated intra-abdominal infections:

  • Single-drug regimens: Piperacillin-tazobactam, ticarcillin-clavulanic acid, or carbapenems (imipenem, meropenem, ertapenem) 1
  • Combination regimens: Ceftriaxone plus metronidazole, or a fluoroquinolone (ciprofloxacin or levofloxacin) plus metronidazole 1

• High-severity community-acquired intra-abdominal infections (APACHE II >15):

  • Broad-spectrum coverage recommended: Meropenem, imipenem-cilastatin, doripenem, piperacillin-tazobactam, or ceftazidime/cefepime plus metronidazole 1
  • Consider anti-enterococcal coverage in healthcare-associated infections 1

• Duration of therapy:

  • For most intra-abdominal infections with adequate source control: 5-7 days 1
  • For patients whose signs and symptoms have resolved: No further antibiotic therapy is required 1

Respiratory Tract Infections

• Exacerbation of chronic bronchitis:
  • First-line (infrequent exacerbations): Amoxicillin, first-generation cephalosporins, macrolides, pristinamycin, or doxycycline 1
  • Second-line (frequent exacerbations or FEV1 <35%): Amoxicillin-clavulanate, cefuroxime-axetil, cefpodoxime-proxetil, or respiratory fluoroquinolones (levofloxacin, moxifloxacin) 1
  • Ciprofloxacin should be reserved for infections with suspected Gram-negative bacilli, particularly Pseudomonas aeruginosa 1

Gastrointestinal Infections

• Pouchitis (after surgery for ulcerative colitis):
  • First choice for acute pouchitis: Ciprofloxacin (preferred over metronidazole due to fewer side effects) 1
  • Alternative: Metronidazole (higher side effect profile) 1
  • No specific antibiotic regimen is recommended for chronic resistant pouchitis 1

Special Considerations

Drug Interactions and Precautions

• Metronidazole:

  • Avoid alcohol during treatment and for at least one day afterward (disulfiram-like reaction) 3
  • May potentiate the effect of warfarin and other oral anticoagulants 3
  • Use cautiously in patients with severe hepatic disease (reduced dosage recommended) 3
  • Monitor patients on lithium therapy for lithium toxicity 3

• Fluoroquinolones (ciprofloxacin):

  • Generally contraindicated in children and adolescents <18 years 1
  • When used for intra-abdominal infections, should be combined with metronidazole for anaerobic coverage 5, 6, 7

• Amoxicillin:

  • May cause allergic reactions in penicillin-sensitive individuals 2
  • Can cause diarrhea, including Clostridioides difficile-associated diarrhea 2

Antibiotic Stewardship

• Obtain appropriate cultures before starting antibiotics when possible to guide targeted therapy 1, 4
• De-escalate to narrower spectrum antibiotics based on culture and susceptibility results 1, 4
• Consider oral step-down therapy when clinically appropriate to reduce hospital stay 1
• Monitor local resistance patterns to guide empiric therapy choices 4

Common Pitfalls to Avoid

• Treating viral infections with antibiotics, which provides no benefit and increases resistance risk 3, 2
• Using fluoroquinolones as first-line therapy when narrower spectrum options are available 1
• Stopping antibiotics prematurely when symptoms improve rather than completing the full course 3, 2
• Using unnecessarily broad-spectrum antibiotics for uncomplicated infections 1, 4
• Failing to adjust therapy based on culture and susceptibility results 1, 4
• Not considering local resistance patterns when selecting empiric therapy 4