What antibiotic should I use for a bacterial infection?

Antibiotic Selection for Bacterial Infections

Direct Answer

The choice of antibiotic depends critically on the specific infection site and severity, but for common bacterial infections, amoxicillin-clavulanate remains the first-line choice for most respiratory and skin infections, while specific pathogens and infection sites require targeted therapy. 1

Infection-Specific Recommendations

Respiratory Tract Infections

For acute bacterial rhinosinusitis in adults with mild disease and no recent antibiotic use (past 4-6 weeks):

• First-line: Amoxicillin-clavulanate (1.75-4 g/250 mg per day) or amoxicillin (1.5-4 g/day) 2
• Alternative options: Cefpodoxime proxetil, cefuroxime axetil, or cefdinir 2
• For β-lactam allergies: TMP/SMX, doxycycline, azithromycin, clarithromycin, or erythromycin, though bacterial failure rates of 20-25% are possible 2

For adults with moderate disease or recent antibiotic use (past 4-6 weeks):

• Respiratory fluoroquinolone (gatifloxacin, levofloxacin, moxifloxacin) or high-dose amoxicillin-clavulanate (4 g/250 mg per day) 2
• Alternative: Ceftriaxone (1-2 g/day IV/IM for 5 days) 2
• Combination therapy options: High-dose amoxicillin or clindamycin plus cefixime, or high-dose amoxicillin or clindamycin plus rifampin 2

For pediatric acute bacterial rhinosinusitis with mild disease and no recent antibiotic use:

• High-dose amoxicillin-clavulanate (90 mg/6.4 mg per kg per day) or high-dose amoxicillin (90 mg/kg per day) 2
• Alternative options: Cefpodoxime proxetil, cefuroxime axetil, or cefdinir 2
• For β-lactam allergies: TMP/SMX, azithromycin, clarithromycin, or erythromycin (with 20-25% bacterial failure rates) 2

For children with moderate disease or recent antibiotic use:

• High-dose amoxicillin-clavulanate (90 mg/6.4 mg per kg per day) or ceftriaxone 2

Skin and Soft Tissue Infections

For non-neutropenic patients:

• Beta-lactams (penicillins, cephalosporins), clindamycin, or TMP-SMX for community-acquired infections 1
• For MRSA coverage: Linezolid, daptomycin, or ceftaroline 2, 1
• Duration: 7-14 days for most bacterial SSTIs 2

For neutropenic patients with suspected or confirmed SSTI:

• Broad-spectrum monotherapy: Carbapenems, antipseudomonal cephalosporins, or piperacillin/tazobactam 2
• Add vancomycin if gram-positive infection suspected or patient hemodynamically unstable 2
• If vancomycin not an option: Daptomycin, ceftaroline, or linezolid 2

Urological Infections

For gonococcal urethritis:

• Ceftriaxone 1 g IM or IV single dose PLUS azithromycin 1 g PO single dose 2
• Alternative for cephalosporin allergy: Gentamicin 240 mg IM single dose plus azithromycin 2 g PO single dose 2

For chlamydial urethritis:

• Azithromycin 1.0-1.5 g PO single dose OR doxycycline 100 mg twice daily for 7 days 2

For non-gonococcal urethritis (unidentified pathogen):

• Doxycycline 100 mg twice daily for 7 days 2

Critical Decision Points

Recent Antibiotic Use

Recent antibiotic exposure (within 4-6 weeks) is a major risk factor for resistant pathogens and necessitates broader-spectrum coverage. 2 This shifts recommendations from amoxicillin alone to amoxicillin-clavulanate or respiratory fluoroquinolones.

Disease Severity Assessment

• Mild disease: Patients more likely to tolerate treatment failure and achieve spontaneous resolution 2
• Moderate disease: Patients require more aggressive therapy and are less likely to tolerate failures 2
• The distinction guides antibiotic selection, not the presence/absence of resistance 2

Failure to Respond at 72 Hours

If no improvement or worsening after 72 hours, either switch to alternate antimicrobial therapy or reevaluate the patient. 2 When switching antibiotics, consider the limitations in coverage of the initial agent 2.

Important Caveats

Beta-Lactam Allergies

• Cephalosporins can be used for penicillin intolerance/non-Type I hypersensitivity reactions (e.g., rash) 2
• For true Type I hypersensitivity reactions, use TMP/SMX, macrolides, or fluoroquinolones, accepting 20-25% bacterial failure rates 2

Fluoroquinolone Stewardship

Widespread use of respiratory fluoroquinolones for milder disease may promote resistance across a wide spectrum of organisms. 2 Reserve these agents for moderate disease or recent antibiotic use.

Rifampin Precautions

Rifampin should never be used as monotherapy, casually, or for longer than 10-14 days, as resistance develops rapidly. 2 It is also a potent cytochrome P450 inducer with high drug interaction potential 2.

Administration Considerations

Amoxicillin-clavulanate should be taken with meals or snacks to reduce gastrointestinal upset. 3 Complete the full course even if symptoms improve early to prevent resistance development 3.