What are the first-line antibiotic treatments for common bacterial infections?

First-Line Antibiotic Treatments for Common Bacterial Infections

The first-line antibiotic treatment for common bacterial infections should be selected based on the suspected pathogen, with amoxicillin, ampicillin, or benzylpenicillin combined with gentamicin recommended for sepsis, high-dose amoxicillin or amoxicillin-clavulanate for respiratory infections, and fluoroquinolones reserved for specific indications. 1

Sepsis and Bloodstream Infections

First-line options:

• Amoxicillin + gentamicin
• Ampicillin + gentamicin
• Benzylpenicillin + gentamicin

Second-line options:

• Amikacin + cloxacillin
• Cefotaxime
• Ceftriaxone

The combination of a penicillin with an aminoglycoside provides coverage against both Gram-positive organisms (including Group B Streptococcus) and Gram-negative bacteria (Enterobacterales) 1.

Respiratory Tract Infections

Acute Bacterial Rhinosinusitis

• First-line (mild disease, no recent antibiotics):

  • Adults: Amoxicillin (1.5-4 g/day) or amoxicillin-clavulanate (1.75-4 g/250 mg per day)
  • Children: High-dose amoxicillin (90 mg/kg/day) or amoxicillin-clavulanate (90 mg/6.4 mg per kg per day) 1

• Alternative options: Cefpodoxime proxetil, cefuroxime axetil, or cefdinir

• For β-lactam allergies: TMP/SMX, doxycycline, azithromycin, clarithromycin, or erythromycin (note: 20-25% bacteriologic failure rate possible) 1

Chronic Bronchitis Exacerbations

• First-line (if at least 2 of 3 Anthonisen criteria present):

  • Amoxicillin
  • First-generation cephalosporins
  • Macrolides
  • Pristinamycin
  • Doxycycline 1

• Second-line (treatment failure or frequent exacerbations):

  • Amoxicillin-clavulanate
  • Cefuroxime-axetil
  • Cefpodoxime-proxetil
  • Cefotiam-hexetil
  • Respiratory fluoroquinolones (levofloxacin, moxifloxacin) 1

Dental Infections

Dental Abscess

• First-line: Amoxicillin 25-50 mg/kg/day divided into three doses 2
• Second-line: Clindamycin 300-450 mg three times daily 2

Important Considerations for Specific Antibiotics

Fluoroquinolones (e.g., Levofloxacin)

• Reserve for specific indications due to risk of serious adverse effects
• Monitor for tendon rupture or swelling, especially in patients >60 years, those on corticosteroids, or with kidney/heart/lung transplants
• Can worsen myasthenia gravis
• Avoid in children under 18 when possible 3

Ceftriaxone

• Monitor prothrombin time in patients with impaired vitamin K synthesis
• Watch for gallbladder pseudolithiasis (especially in pediatric patients)
• Ensure adequate hydration to prevent urolithiasis
• Monitor for pancreatitis, especially in patients with risk factors for biliary stasis 4

Azithromycin

• Use caution in patients with impaired hepatic function
• Can exacerbate symptoms of myasthenia gravis
• May potentiate effects of oral anticoagulants
• Avoid aluminum and magnesium-containing antacids simultaneously 5

Antibiotic Selection Algorithm

1. Identify infection site and likely pathogens
2. Consider patient factors:
   • Age
   • Allergies
   • Comorbidities (renal/hepatic function)
   • Recent antibiotic exposure
   • Local resistance patterns
3. Select appropriate first-line agent based on guidelines
4. Reassess after 48-72 hours:
   • If improving: complete course
   • If not improving: switch to second-line therapy or reevaluate diagnosis

Common Pitfalls to Avoid

• Overuse of broad-spectrum antibiotics when narrow-spectrum would suffice
• Inadequate dosing leading to treatment failure and resistance
• Failure to adjust therapy based on culture results when available
• Inappropriate duration of therapy (too short or too long)
• Neglecting local resistance patterns when selecting empiric therapy

Remember that penicillin, cloxacillin, and erythromycin should cover approximately 90% of Gram-positive infections 6, while more targeted therapy is needed for Gram-negative and anaerobic infections.