What are the first and second line antibiotics for common bacterial and viral infections?

First-Line and Second-Line Antibiotics for Common Bacterial and Viral Infections

The most appropriate first-line antibiotics for common bacterial infections are typically narrow-spectrum Access category drugs, while viral infections generally do not require antibiotic treatment as antibiotics are ineffective against viruses. 1

Bacterial Infections

Respiratory Tract Infections

Pharyngitis (Sore Throat)

• First choice:
  • Watchful waiting with symptom relief (no antibiotics) for suspected viral cases
  • Amoxicillin or phenoxymethylpenicillin for suspected bacterial (Group A Streptococcal) cases 1
• Second choice:
  • Cefalexin or clarithromycin (for penicillin allergy) 1

Acute Otitis Media

• First choice:
  • Watchful waiting for most cases (especially in children >2 years)
  • Amoxicillin if antibiotics indicated 1
• Second choice:
  • Amoxicillin-clavulanic acid 1

Community-Acquired Pneumonia

• First choice:
  • Amoxicillin or amoxicillin-clavulanic acid 1
• Second choice:
  • Macrolides (azithromycin, clarithromycin) or doxycycline 1
  • Respiratory fluoroquinolones for severe cases 1

Gastrointestinal Infections

Bacterial Diarrhea/Traveler's Diarrhea

• First choice:
  • Ciprofloxacin or azithromycin 1
• Second choice:
  • Trimethoprim-sulfamethoxazole (where resistance is low) 1

Enteric (Typhoid) Fever

• First choice:
  • Fluoroquinolones (ciprofloxacin, ofloxacin) for susceptible strains 1
• Second choice:
  • Azithromycin or third-generation cephalosporins (ceftriaxone) 1

Urinary Tract Infections

Uncomplicated Lower UTI

• First choice:
  • Nitrofurantoin, fosfomycin, or pivmecillinam 2
• Second choice:
  • Trimethoprim-sulfamethoxazole (if local resistance <20%)
  • Oral cephalosporins (cephalexin, cefixime) 2

Complicated UTI/Pyelonephritis

• First choice:
  • Fluoroquinolones (ciprofloxacin) 3
• Second choice:
  • Third-generation cephalosporins (ceftriaxone) 4
  • Amoxicillin-clavulanic acid 1

Skin and Soft Tissue Infections

Cellulitis/Impetigo/Erysipelas

• First choice:
  • Dicloxacillin or other penicillinase-resistant penicillins 5
• Second choice:
  • First-generation cephalosporins (cefalexin) 1
  • Clindamycin (for penicillin allergy) 6

Bone and Joint Infections (Osteomyelitis)

• First choice:
  • Clindamycin for non-MRSA infections 6
• Second choice:
  • Trimethoprim-sulfamethoxazole for MRSA 6
  • Linezolid for resistant cases 6

Viral Infections

Important: Antibiotics are ineffective against viral infections and should not be used unless there is evidence of bacterial co-infection or superinfection. 7, 8

Common Viral Infections That Do NOT Require Antibiotics:

• Common cold
• Viral pharyngitis
• Influenza
• Viral bronchitis
• Most cases of acute sinusitis
• Viral gastroenteritis

Special Considerations for Viral Infections:

Viral Respiratory Infections

• First approach: Symptomatic treatment only
• When to consider antibiotics: Only if clear evidence of bacterial superinfection (persistent fever >3-5 days, purulent sputum, focal chest findings) 7

Viral Meningitis/Encephalitis

• Initial approach: If bacterial meningitis cannot be ruled out, empiric antibiotics should be started while awaiting culture results 7
• First choice for empiric therapy: Ceftriaxone plus vancomycin 4

Common Pitfalls to Avoid

1. Treating viral infections with antibiotics - This contributes to antibiotic resistance and provides no benefit to patients 1

2. Using broad-spectrum antibiotics when narrow-spectrum would suffice - Always prefer Access category antibiotics when appropriate 1

3. Not considering local resistance patterns - Local antibiograms should guide empiric therapy, especially for UTIs and respiratory infections 2

4. Inappropriate duration of therapy - Most uncomplicated infections require only 5-7 days of treatment; longer courses increase resistance risk 6

5. Not adjusting therapy based on culture results - Always narrow therapy when culture results become available 1

6. Using fluoroquinolones as first-line therapy - These should be reserved for specific indications due to resistance concerns and adverse effects 1, 3

7. Failing to recognize when surgical intervention is needed - Particularly important in osteomyelitis and complicated skin infections 6

Remember that antibiotic selection should follow the AWaRe (Access, Watch, Reserve) framework, with preference given to Access antibiotics whenever possible to reduce antimicrobial resistance 1.