What antibiotics are indicated for acute infections?

Antibiotics for Acute Infections

For acute infections, antibiotic selection should be based on the site of infection, suspected pathogens, and patient factors, with treatment regimens targeting the most likely organisms while considering local resistance patterns. 1

Skin and Soft Tissue Infections

Nonpurulent Cellulitis

• First-line therapy: 5-6 day course of antibiotics active against streptococci 1
  • Amoxicillin 500 mg three times daily
  • Cephalexin 500 mg four times daily
  • Clindamycin 300-450 mg three times daily (if penicillin allergic)

Purulent Skin Infections (Abscess)

• Primary treatment: Incision and drainage 1
• Adjunctive antibiotics (if systemic symptoms, extensive disease, or immunocompromised):
  • MRSA coverage: Trimethoprim-sulfamethoxazole, doxycycline, or linezolid
  • For severe infections: Vancomycin IV 15-20 mg/kg every 12 hours 2

Severe/Necrotizing Infections

• Broad empiric coverage required 1:
  • Vancomycin 15-20 mg/kg IV every 12 hours PLUS
  • Piperacillin-tazobactam 4.5g IV every 6-8 hours OR
  • Carbapenem (meropenem, imipenem) OR
  • Ceftriaxone 2g IV daily PLUS metronidazole 500 mg IV every 8 hours

Respiratory Tract Infections

Community-Acquired Pneumonia

• Outpatient treatment:
  • Amoxicillin 1g three times daily (first-line) 1
  • Macrolide (if atypical pathogens suspected or in patients >3 years) 1
  • Amoxicillin-clavulanate or respiratory fluoroquinolone (if risk factors present)

Acute Bronchitis

• Antibiotics generally not indicated (usually viral) 1
• If bacterial superinfection suspected in high-risk patients:
  • Amoxicillin-clavulanate 875/125 mg twice daily
  • Doxycycline 100 mg twice daily

Acute Sinusitis

• First-line 1:
  • Amoxicillin-clavulanate 875/125 mg twice daily
  • Cefuroxime axetil 250-500 mg twice daily
  • Cefpodoxime proxetil 200 mg twice daily

Urinary Tract Infections

Uncomplicated Cystitis

• First-line options 1:
  • Nitrofurantoin 100 mg twice daily for 5 days
  • Trimethoprim-sulfamethoxazole 160/800 mg twice daily for 3 days
  • Fosfomycin 3g single dose

Pyelonephritis

• Outpatient treatment 1:
  • Fluoroquinolones (e.g., ciprofloxacin 500-750 mg twice daily) for 5-7 days
  • Trimethoprim-sulfamethoxazole for 14 days (if susceptibility confirmed)

Diabetic Foot Infections

Mild Infections

• Oral options 1:
  • Dicloxacillin 500 mg four times daily
  • Cephalexin 500 mg four times daily
  • Clindamycin 300-450 mg three times daily
  • Amoxicillin-clavulanate 875/125 mg twice daily

Moderate/Severe Infections

• Parenteral options 1:
  • Ceftriaxone 1-2g daily
  • Ertapenem 1g daily
  • Levofloxacin 750 mg daily + clindamycin 600-900 mg every 8 hours
  • For MRSA coverage: Add vancomycin, linezolid, or daptomycin

Intra-abdominal Infections

Community-acquired infections

• First-line options 1:
  • Cefazolin or cefoxitin + metronidazole
  • Ciprofloxacin + metronidazole
  • Ampicillin-sulbactam

Healthcare-associated infections

• Broad-spectrum coverage 1:
  • Piperacillin-tazobactam
  • Imipenem-cilastatin or meropenem
  • Cefepime + metronidazole

Important Considerations

Duration of Therapy

• Shorter courses are often sufficient 1:
  • Cellulitis: 5-6 days
  • Pyelonephritis: 5-7 days (fluoroquinolones) or 14 days (TMP-SMX)
  • Sinusitis: 5-10 days
  • Community-acquired pneumonia: 5-7 days

Administration Method

• For severe infections, consider prolonged infusion of beta-lactams (extended ≥3 hours or continuous 24-hour infusion) rather than intermittent dosing for improved outcomes 3

Special Populations

• Immunocompromised patients: Use broader spectrum agents with lower thresholds for hospitalization and IV therapy
• Elderly patients: Consider renal dosing adjustments and drug interactions
• Pregnant women: Avoid fluoroquinolones, tetracyclines, and other contraindicated agents

Common Pitfalls to Avoid

1. Treating viral infections with antibiotics (especially acute bronchitis and viral URI)
2. Using fluoroquinolones as first-line therapy when narrower spectrum options are appropriate
3. Inadequate source control for abscesses and other collections (surgical drainage is primary therapy)
4. Failing to adjust therapy based on culture results when available
5. Excessive duration of antibiotic therapy when shorter courses are equally effective

When selecting antibiotics, always consider local resistance patterns, patient allergies, and previous antibiotic exposure to guide optimal therapy.