What antibiotics are used to treat common bacterial infections?

Antibiotics for Common Bacterial Infections

For common bacterial infections, first-line antibiotics should be selected based on the specific infection type, likely pathogens, and local resistance patterns, with preference for narrow-spectrum agents when appropriate.

Urinary Tract Infections

Uncomplicated Cystitis in Women

• First-line options:
  • Nitrofurantoin for 5 days
  • Trimethoprim-sulfamethoxazole (TMP-SMX) for 3 days
  • Fosfomycin as a single dose 1
• Fluoroquinolones should be reserved for patients with resistant organisms due to their high propensity for adverse effects 1
• E. coli accounts for >75% of bacterial cystitis cases, making it the primary target for empiric therapy 1

Uncomplicated Pyelonephritis

• First-line options:
  • Fluoroquinolones for 5-7 days (if susceptible)
  • TMP-SMX for 14 days (based on susceptibility testing) 1
• Recent studies show 5-day courses of fluoroquinolones are as effective as 10-day courses, with clinical cure rates >93% 1
• TMP-SMX should not be used empirically without culture and susceptibility testing due to resistance concerns 1

Skin and Soft Tissue Infections

Nonpurulent Cellulitis

• Recommended treatment: 5-6 day course of antibiotics active against streptococci 1
• Common options include cephalosporins, penicillins, or clindamycin 1
• For MRSA concerns (penetrating trauma, prior MRSA infection, injection drug use), add coverage effective against both MRSA and streptococci 1

Impetigo and Other Skin Infections

• First-line options:
  • Dicloxacillin, cefalexin, erythromycin, clindamycin, or amoxicillin-clavulanic acid 1
• For MRSA infections: vancomycin, linezolid, clindamycin, daptomycin, ceftaroline, doxycycline, or TMP-SMX 1
• For animal or human bites: amoxicillin-clavulanic acid is preferred 1

Respiratory Tract Infections

Sinusitis

• First-line options for maxillary sinusitis:
  • Amoxicillin-clavulanate
  • Second and third generation cephalosporins (cefuroxime-axetil, cefpodoxime-proxetil, cefotiam-hexetil)
  • Pristinamycin (for penicillin allergy) 1
• For frontal, ethmoidal, or sphenoidal sinusitis:
  • Same as above, or
  • Fluoroquinolones active against pneumococci (levofloxacin, moxifloxacin) 1
• Treatment duration is typically 7-10 days, though some cephalosporins have shown efficacy in 5 days 1

Acute Otitis Media and Pharyngotonsillitis

• First-line options:
  • Amoxicillin/clavulanic acid
  • Cefaclor
  • Azithromycin (3-day course has shown comparable efficacy to longer courses) 2, 3

Special Considerations

Methicillin-Resistant Staphylococcus aureus (MRSA)

• For complicated MRSA infections:
  • Vancomycin (30-60 mg/kg/day IV in 2-4 divided doses)
  • Teicoplanin (loading dose followed by daily maintenance)
  • Linezolid (600 mg IV/PO q12h)
  • Daptomycin (4-6 mg/kg/dose IV daily) 1
• For outpatient MRSA skin infections:
  • TMP-SMX (160-320/800-1600 mg PO q12h)
  • Doxycycline (100 mg PO q12h)
  • Minocycline (200 mg loading, then 100 mg PO q12h)
  • Fusidic acid (500 mg PO q8-12h or 750 mg q12h) 1

Doxycycline Indications

• Effective for respiratory infections caused by Mycoplasma pneumoniae
• Treatment of choice for many rickettsial infections (Rocky Mountain spotted fever, typhus)
• Useful for Chlamydia infections, including trachoma and urethritis
• Effective against certain gram-negative infections including Haemophilus influenzae respiratory infections 4

Antibiotic Stewardship Principles

AWaRe Classification

• Access antibiotics: First-line options with good activity against common pathogens and lower resistance potential; should be widely available
• Watch antibiotics: Higher risk for selecting resistant bacteria; targets for monitoring and stewardship
• Reserve antibiotics: Last-resort options for multidrug-resistant infections 1

Duration of Therapy

• Shorter courses (when evidence-supported) decrease overall antibiotic exposure, reducing selection pressure for resistant organisms and risk of adverse effects 1
• Contrary to common belief, taking antibiotics beyond symptom resolution does not reduce antibiotic resistance; prolonged use actually increases resistance due to selection pressure 1

Common Pitfalls to Avoid

• Overuse of fluoroquinolones: Despite efficacy, fluoroquinolones should be reserved for specific indications due to adverse effects and resistance concerns 1
• Defaulting to 10-day courses: Many infections can be effectively treated with shorter courses, which reduces adverse effects and resistance development 1
• Empiric broad-spectrum therapy without culture: When possible, obtain cultures before starting antibiotics, especially for severe infections 1
• Ignoring local resistance patterns: Local epidemiology should guide empiric therapy choices, particularly for UTIs and skin infections 1