What antibiotic is used to treat which type of infection?

Antibiotic Selection Guide for Different Types of Infections

The most appropriate antibiotic for treatment depends on the specific infection type, suspected pathogens, and patient factors, with empiric therapy guided by local resistance patterns until culture results are available. 1

Skin and Soft Tissue Infections

Mild to Moderate Infections

• For simple skin infections: Amoxicillin-clavulanic acid or cloxacillin are first-line choices 2
• For impetigo: Dicloxacillin, cephalexin, clindamycin, or amoxicillin-clavulanate are recommended 1
• For MRSA infections (outpatient): Trimethoprim-sulfamethoxazole, doxycycline, minocycline, or fusidic acid 2

Severe Infections

• For necrotizing fasciitis: Combination therapy with vancomycin or linezolid plus piperacillin-tazobactam or a carbapenem, or ceftriaxone plus metronidazole 2
• For inpatient MRSA infections: Vancomycin (30-60 mg/kg/day IV in divided doses) or teicoplanin (6-12 mg/kg/dose IV q12h for three doses, then daily) 2
• For specific pathogens in necrotizing infections:
  • Streptococcus: Penicillin plus clindamycin
  • S. aureus: Nafcillin, oxacillin, cefazolin, vancomycin, or clindamycin
  • Clostridium species: Clindamycin plus penicillin 2

Animal and Human Bites

• Animal bites: Amoxicillin-clavulanic acid (oral) or ampicillin-sulbactam, piperacillin-tazobactam (IV) 2
• Human bites: Amoxicillin-clavulanic acid or ampicillin-sulbactam; carbapenems and doxycycline as alternatives 2

Diabetic Foot Infections

• Mild infections: Dicloxacillin, clindamycin, cephalexin, levofloxacin, amoxicillin-clavulanate, or doxycycline 2
• Moderate to severe infections: Levofloxacin, cefoxitin, ceftriaxone, ampicillin-sulbactam, moxifloxacin, ertapenem, tigecycline, or ciprofloxacin with clindamycin 2
• For suspected or confirmed MRSA: Linezolid, daptomycin, or vancomycin 2
• For potential Pseudomonas aeruginosa infection: Piperacillin-tazobactam, ceftazidime, cefepime, aztreonam, or carbapenems 2

Intra-abdominal Infections

Community-Acquired Infections (Extra-biliary)

• Mild-to-moderate severity: Cefoxitin, ertapenem, moxifloxacin, tigecycline, or ticarcillin-clavulanic acid 2
• Combination therapy options: Cefazolin, cefuroxime, ceftriaxone, cefotaxime, ciprofloxacin, or levofloxacin, each with metronidazole 2
• High risk or severe infections: Imipenem-cilastatin, meropenem, doripenem, or piperacillin-tazobactam 2

Surgical Site Infections

• Intestinal/genitourinary tract: Ticarcillin-clavulanic acid, piperacillin-tazobactam, carbapenems, or combination regimens (ceftriaxone + metronidazole, fluoroquinolone + metronidazole) 2
• Trunk/extremity (away from axilla/perineum): Oxacillin, nafcillin, cefazolin, cefalexin, sulfamethoxazole-trimethoprim, or vancomycin 2
• Axilla/perineum: Ceftriaxone or fluoroquinolone with metronidazole 2

Respiratory Tract Infections

Community-Acquired Pneumonia

• Children <3 years: Amoxicillin 80-100 mg/kg/day in three daily doses 2
• Children >3 years:
  • For suspected pneumococcal infection: Amoxicillin
  • For suspected atypical pathogens: Macrolides 2

Acute Bronchitis and Exacerbations of Chronic Bronchitis

• First-line antibiotics for infrequent exacerbations: Amoxicillin, first-generation cephalosporins, macrolides, pristinamycin, or doxycycline 2
• Second-line antibiotics for frequent exacerbations or treatment failure: Amoxicillin-clavulanate, cefuroxime-axetil, cefpodoxime-proxetil, or respiratory fluoroquinolones (levofloxacin, moxifloxacin) 2

Special Considerations

Doxycycline Indications

• Indicated for respiratory tract infections caused by Mycoplasma pneumoniae 3
• Effective for specific infections including Rocky Mountain spotted fever, Q fever, and chlamydial infections 3
• Used in combination therapy for Aeromonas hydrophila (doxycycline plus ciprofloxacin or ceftriaxone) and Vibrio vulnificus (doxycycline plus ceftriaxone or cefotaxime) 2

Fluoroquinolone Considerations

• Levofloxacin is indicated for community-acquired pneumonia, acute sinus infection, acute worsening of chronic bronchitis, skin infections, urinary tract infections, and kidney infections 4
• Serious side effects include tendon rupture, worsening of myasthenia gravis, and CNS effects 4
• Should be used with caution in patients with risk factors for tendon problems (age >60, steroid use, kidney/heart/lung transplant) 4

Common Pitfalls to Avoid

• Failing to adjust therapy based on culture results when available 1
• Using unnecessarily broad-spectrum antibiotics for uncomplicated infections 1
• Not considering local resistance patterns when selecting empiric therapy 1
• Insufficient duration of therapy for deep-seated infections 1
• Not recognizing the need for surgical intervention in necrotizing infections, which is as important as antibiotic selection 2

Duration of Therapy

• Skin and soft tissue infections: 5-10 days for uncomplicated infections; 7-14 days for complicated infections 2
• Bacteremia: 2 weeks for uncomplicated; 4-6 weeks for complicated 2
• Endocarditis: 4-6 weeks 2
• Shorter courses of antibiotics may be as effective as longer courses for many infections, which can help reduce antibiotic resistance 5