What are the typical antibiotics, dosages, and frequencies for common bacterial infections?

Antibiotic Selection, Dosing, and Frequency for Common Bacterial Infections

The optimal antibiotic selection, dosage, and frequency for bacterial infections should be based on the specific pathogen, infection site, severity, and patient factors, with treatment guided by local susceptibility patterns whenever possible. 1

General Principles for Antibiotic Selection

• Choose the narrowest effective agent to reduce resistance development
• Consider patient factors (age, pregnancy, renal function) when selecting antibiotics
• Obtain appropriate cultures before starting antibiotics when possible
• Use the shortest effective duration to minimize resistance development
• Adjust therapy based on culture results when available

Common Bacterial Infections and First-Line Treatments

Respiratory Tract Infections

Community-Acquired Pneumonia

• Streptococcus pneumoniae (penicillin-susceptible)

  • Penicillin G: 200,000-300,000 U/kg/day IV divided q4h (up to 12-24 million U daily)
  • Amoxicillin: 1g PO q8h for 5-7 days 2

• Atypical Pathogens (Mycoplasma, Chlamydophila)

  • Doxycycline: 100mg PO/IV q12h for 7-14 days
  • Alternative: Azithromycin 500mg PO day 1, then 250mg PO daily for 4 days 2

• MRSA Pneumonia

  • Vancomycin: 15-20 mg/kg/dose IV q8-12h (adults), 15 mg/kg/dose IV q6h (children)
  • Alternative: Linezolid 600mg PO/IV q12h (adults), 10 mg/kg/dose PO/IV q8h (children, not exceeding 600mg/dose) 2

Skin and Soft Tissue Infections

Uncomplicated Skin Infections

• Purulent cellulitis (likely MRSA)

  • TMP-SMX: 1-2 DS tablets PO q12h for 5-10 days
  • Clindamycin: 300-450mg PO q8h for 5-10 days 2, 3

• Non-purulent cellulitis (likely streptococcal)

  • Cephalexin: 500mg PO q6h for 5-10 days
  • Dicloxacillin: 500mg PO q6h for 5-10 days 2

Complicated Skin Infections

• Vancomycin: 15-20 mg/kg/dose IV q8-12h (adults), 15 mg/kg/dose IV q6h (children)
• Daptomycin: 4 mg/kg/dose IV daily (adults) 2

Urinary Tract Infections

Uncomplicated UTI

• TMP-SMX: 160/800mg (1 DS tablet) PO q12h for 3 days
• Ciprofloxacin: 250-500mg PO q12h for 3 days 4

Complicated UTI

• Ciprofloxacin: 500mg PO q12h for 7-14 days
• Ceftriaxone: 1-2g IV q24h for 7-14 days 4

Bloodstream Infections

• Vancomycin: 15-20 mg/kg/dose IV q8-12h (MRSA)
• Ceftriaxone: 2g IV q24h (gram-negative organisms)
• Duration: 7 days is as effective as 14 days for most uncomplicated bacteremia 5

Bone and Joint Infections

Osteomyelitis

• MSSA: Nafcillin/oxacillin 2g IV q4-6h for ≥6 weeks
• MRSA: Vancomycin 15-20 mg/kg/dose IV q8-12h for ≥6 weeks
• Alternative: Daptomycin 6 mg/kg/day IV daily for ≥6 weeks 2

Septic Arthritis

• MSSA: Nafcillin/oxacillin 2g IV q4-6h for 3-4 weeks
• MRSA: Vancomycin 15-20 mg/kg/dose IV q8-12h for 3-4 weeks 2

Infective Endocarditis

Native Valve (Streptococcal)

• Penicillin G: 200,000-300,000 U/kg/day IV divided q4h for 4 weeks
• Alternative: Ceftriaxone 2g IV daily for 4 weeks 2

Native Valve (MRSA)

• Vancomycin: 30-60 mg/kg/day IV in divided doses for 6 weeks 2

Prosthetic Valve

• Vancomycin + Rifampin + Gentamicin:
  • Vancomycin: 15-20 mg/kg/dose IV q8-12h
  • Rifampin: 300mg PO q8h
  • Gentamicin: 1 mg/kg/dose IV q8h for 2 weeks, then continue vancomycin and rifampin for 6 weeks 2

Special Considerations

Pediatric Dosing

• Doxycycline: For children >8 years, 2 mg/lb on first day divided in two doses, then 1 mg/lb daily 6
• Clindamycin: 8-16 mg/kg/day divided into 3-4 doses for serious infections; 16-20 mg/kg/day for severe infections 3
• Vancomycin: 15 mg/kg/dose IV q6h 2

Common Pitfalls to Avoid

• Using antibiotics for viral infections
• Selecting overly broad-spectrum agents when narrower options are appropriate
• Failing to adjust dosing for renal impairment
• Not completing the full treatment course for certain infections (e.g., streptococcal pharyngitis)
• Neglecting to de-escalate therapy once culture results are available

Duration of Therapy

• Respiratory infections: 5-7 days
• Skin and soft tissue infections: 5-10 days
• Urinary tract infections: 3-7 days
• Bloodstream infections: 7-14 days (7 days for uncomplicated)
• Bone/joint infections: ≥4-6 weeks
• Endocarditis: 4-6 weeks 2, 1

Antibiotic Selection Algorithm

1. Identify the likely pathogen based on infection site and clinical presentation
2. Consider local resistance patterns
3. Select the narrowest spectrum agent effective against the suspected pathogen
4. Adjust for patient factors (allergies, renal/hepatic function, pregnancy)
5. Optimize dosing based on pharmacokinetic/pharmacodynamic principles
6. Reassess therapy at 48-72 hours based on clinical response and culture results
7. De-escalate to targeted therapy when possible
8. Continue for the appropriate duration based on infection type and clinical response

Remember that antibiotic selection should always prioritize agents with the narrowest effective spectrum to minimize resistance development while ensuring adequate treatment of the infection.