What antibiotics are used to treat common bacterial infections?

Antibiotics for Common Bacterial Infections

For most common bacterial infections, use Access antibiotics as first-line therapy: amoxicillin or amoxicillin-clavulanate for respiratory infections, trimethoprim-sulfamethoxazole or nitrofurantoin for uncomplicated UTIs, and reserve fluoroquinolones and broad-spectrum agents only when narrower options fail or resistance patterns demand them. 1, 2

Respiratory Tract Infections

Community-Acquired Pneumonia (CAP)

• For healthy adults without comorbidities: Use amoxicillin, doxycycline, or a macrolide (azithromycin, clarithromycin) for 5 days minimum 1
• For adults with comorbidities: Use a β-lactam (amoxicillin-clavulanate) plus a macrolide, OR a respiratory fluoroquinolone (levofloxacin, moxifloxacin) 1, 2
• Treatment duration: Minimum 5 days, extending only if clinical stability criteria are not met (persistent fever >48 hours, inability to eat, abnormal vital signs, altered mentation) 1
• Predicted efficacy in adults: Respiratory quinolones and high-dose amoxicillin-clavulanate achieve 90-92% clinical success, while standard-dose amoxicillin achieves 83-88% 1

Acute Bacterial Rhinosinusitis

• First-line for adults: High-dose amoxicillin (4g/day) or amoxicillin-clavulanate (1.75-4g/250mg per day) 1
• Alternative options: Cefpodoxime, cefuroxime, cefdinir, or trimethoprim-sulfamethoxazole 1
• Short-course options: 3 days of azithromycin or 5 days of cefpodoxime, telithromycin, or gatifloxacin 3
• For treatment failures at 72 hours: Switch based on initial therapy spectrum—if started on amoxicillin, escalate to amoxicillin-clavulanate or respiratory fluoroquinolone 1

COPD Exacerbations and Acute Bronchitis

• Treat only if bacterial infection is likely: Increased sputum purulence PLUS increased dyspnea and/or increased sputum volume 1
• First-line antibiotics: Amoxicillin-clavulanate, macrolides (azithromycin, clarithromycin), or tetracyclines (doxycycline) 1, 4
• Duration: 5 days is sufficient—no difference in outcomes between 4.9 days versus 8.3 days 1
• Common pathogens: Haemophilus influenzae, Streptococcus pneumoniae, Moraxella catarrhalis 1

Urinary Tract Infections

Uncomplicated Cystitis (Women)

• First-line options:
  • Nitrofurantoin for 5 days 1
  • Trimethoprim-sulfamethoxazole (TMP-SMX) for 3 days 1
  • Fosfomycin as single dose 1
• Avoid fluoroquinolones as first-line due to resistance concerns and FDA warnings about serious adverse effects 1

Uncomplicated Pyelonephritis

• First-line: Fluoroquinolones (ciprofloxacin, levofloxacin) for 5-7 days based on local susceptibility 1
• Alternative: TMP-SMX for 14 days if organism is susceptible 1
• Primary pathogen: Escherichia coli accounts for >75% of cases 1

Gastrointestinal Infections

Acute Infectious Bacterial Diarrhea

• General principle: Antibiotics are NOT routinely recommended for most bacterial diarrhea 1
• Traveler's diarrhea: Use antibiotics only if likelihood of bacterial pathogens justifies potential adverse effects—options include fluoroquinolones, azithromycin, or rifaximin 1
• Confirmed Shigella infections: Ceftriaxone (Watch antibiotic) is more effective than fluoroquinolones; β-lactams show superior outcomes (RR 4.68,95% CI 1.74-12.59) 1
• Cholera: Azithromycin first-line, doxycycline as alternative; avoid TMP-SMX (less effective than doxycycline) 1
• AVOID antibiotics in enterohemorrhagic E. coli due to increased risk of hemolytic uremic syndrome 1

Skin and Soft Tissue Infections

Impetigo and Non-Purulent Infections

• First-line oral agents: Dicloxacillin, cefalexin, clindamycin, or amoxicillin-clavulanate 2, 4
• For β-lactam allergies: Clindamycin or erythromycin 4

Purulent Infections (Suspected Staphylococcus aureus)

• First-line: Dicloxacillin, cefazolin, cefalexin, clindamycin, doxycycline, or TMP-SMX 4
• For MRSA coverage: Vancomycin, linezolid, daptomycin, or ceftaroline 2, 4
• Evidence note: Linezolid shows better clinical cure than vancomycin (OR 1.41,95% CI 1.03-1.95) 4

Necrotizing Fasciitis

• Empiric regimen: Vancomycin or linezolid PLUS piperacillin-tazobactam or a carbapenem 4
• Alternative: Ceftriaxone plus metronidazole 4

Intra-Abdominal Infections

Mild to Moderate Infections

• First-line: Amoxicillin-clavulanate 2, 4
• Alternative: Ampicillin plus gentamicin plus metronidazole (particularly in children) 4

Severe Infections

• First-line: Ceftriaxone or cefotaxime plus metronidazole, OR piperacillin-tazobactam 2, 4
• Hospital-acquired/critically ill: Piperacillin-tazobactam, tigecycline, or carbapenems (meropenem, imipenem, doripenem) 4

Key Stewardship Principles

AWaRe Classification Framework

• Access antibiotics (first-line): Amoxicillin, amoxicillin-clavulanate, benzylpenicillin, cefalexin, clindamycin, gentamicin, metronidazole, TMP-SMX 1, 2
• Watch antibiotics (specific indications only): Fluoroquinolones, third-generation cephalosporins, macrolides, carbapenems 1
• Reserve antibiotics (last-resort only): For multidrug-resistant organisms when all other options have failed 1

Duration of Therapy

• Most community-acquired infections: 5-7 days is sufficient 4
• Severe infections: May require 10-14 days 4
• Clinical stability criteria should guide extension beyond minimum duration, not arbitrary day counts 1

Common Pitfalls to Avoid

• Do NOT use fluoroquinolones as first-line for common infections—FDA has issued strengthened warnings about serious adverse effects including tendon rupture, peripheral neuropathy, and CNS effects 1, 5
• Do NOT prescribe antibiotics for viral bronchitis unless clear bacterial signs present (purulent sputum plus increased dyspnea/volume) 1, 6
• Do NOT extend antibiotic duration beyond evidence-based minimums without documented clinical instability—93% of excess duration occurs at discharge 1
• Do NOT use antibiotics for gastroenteritis even if bacterial, as this prolongs carrier state and risks superinfection 1
• Reassess diagnosis if patient not improving rather than reflexively extending duration 1

Monitoring and De-escalation

• Expect clinical improvement within 3 days of appropriate therapy 4
• De-escalate based on culture results and clinical response at 2-4 days 2
• Check local resistance patterns before selecting empiric therapy, particularly for TMP-SMX and fluoroquinolones 1