What are the most common doses for bacterial infections?

Common Antibiotic Doses for Bacterial Infections

For most common bacterial infections, use amoxicillin-clavulanate 875/125 mg PO every 12 hours for adults, or 45 mg/kg/day divided every 12 hours for children, as this provides broad-spectrum coverage with optimal dosing convenience and reduced gastrointestinal side effects. 1

Respiratory Tract Infections

Community-Acquired Pneumonia

Streptococcus pneumoniae (Penicillin MIC <2 mg/L):

• Preferred: Amoxicillin 1 g PO every 8 hours, or Amoxicillin-clavulanate 1.2 g IV/PO every 12 hours 2
• Alternative: Ceftriaxone 1-2 g IV every 12 hours, Levofloxacin 750 mg IV/PO daily, or Moxifloxacin 400 mg IV/PO daily 2
• Duration: 5-7 days for uncomplicated cases 2

Atypical Pathogens (Mycoplasma, Chlamydophila):

• Mycoplasma: Doxycycline 100 mg IV/PO every 12 hours for 7-14 days (preferred), or Azithromycin 500 mg PO day 1, then 250 mg daily for 4 days 2
• Chlamydophila: Azithromycin 500 mg PO day 1, then 250 mg daily for 4 days, or Levofloxacin 500-750 mg PO/IV daily for 7-10 days 2

Legionella species:

• Levofloxacin 750 mg IV/PO daily or Moxifloxacin 400 mg IV/PO daily 2

Haemophilus influenzae

• β-lactamase negative: Amoxicillin 1 g PO every 8 hours 2
• β-lactamase positive: Amoxicillin-clavulanate 1.2 g IV/PO every 12 hours, or Ceftriaxone 2 g IV daily 2

Skin and Soft Tissue Infections

Methicillin-Susceptible Staphylococcus aureus (MSSA)

• Parenteral: Nafcillin or Oxacillin 1-2 g IV every 4 hours, or Cefazolin 1-2 g IV every 8 hours 2
• Oral: Dicloxacillin 500 mg PO 4 times daily, or Cephalexin 500 mg PO 4 times daily 2
• Duration: 5-10 days depending on severity 2

Methicillin-Resistant Staphylococcus aureus (MRSA)

Outpatient SSTI:

• TMP-SMX 160-320/800-1600 mg PO every 12 hours, or Doxycycline 100 mg PO every 12 hours 2
• Linezolid 600 mg PO every 12 hours for more severe cases 2

Inpatient/Complicated SSTI:

• Vancomycin 30-60 mg/kg/day IV divided every 6-12 hours (target trough 15-20 mcg/mL), with a loading dose of 25-30 mg/kg for seriously ill patients 2, 3
• Alternative: Teicoplanin 6-12 mg/kg IV every 12 hours for 3 doses, then daily; or Linezolid 600 mg IV/PO every 12 hours 2
• Duration: 7-14 days 2

Necrotizing Infections (Mixed)

• Piperacillin-tazobactam 3.375 g IV every 6-8 hours PLUS Vancomycin 30-60 mg/kg/day IV divided 2
• Alternative: Meropenem 1 g IV every 8 hours, or Imipenem-cilastatin 1 g IV every 6-8 hours 2

Streptococcal Necrotizing Fasciitis

• Penicillin G 2-4 million units IV every 4-6 hours PLUS Clindamycin 600-900 mg IV every 8 hours 2

Intra-Abdominal Infections

Empiric Therapy:

• Piperacillin-tazobactam 3.375 g IV every 6 hours (or 4.5 g every 6 hours for Pseudomonas coverage) 2
• Alternative: Meropenem 1 g IV every 8 hours, Imipenem-cilastatin 500 mg IV every 6 hours, or Ertapenem 1 g IV daily 2
• For less severe community-acquired: Cefotaxime 1-2 g IV every 6-8 hours PLUS Metronidazole 500 mg IV every 8-12 hours 2
• Duration: 4-7 days unless source control is inadequate 2

Bacteremia and Endocarditis

MRSA Bacteremia

• Uncomplicated: Vancomycin 30-60 mg/kg/day IV divided every 6-12 hours for 7-14 days 2
• Complicated: Vancomycin 30-60 mg/kg/day IV divided, or Daptomycin 6-10 mg/kg IV daily for 4-6 weeks 2
• Critical pitfall: Never add gentamicin or rifampin to vancomycin for uncomplicated bacteremia 2, 3

Endocarditis

• MRSA native valve: Vancomycin 30-60 mg/kg/day IV divided for 4-6 weeks 2
• MRSA prosthetic valve: Vancomycin 30-60 mg/kg/day IV divided PLUS Rifampin 300 mg PO every 8 hours PLUS Gentamicin 1 mg/kg IV every 8 hours for 6 weeks 2
• Streptococcal (highly susceptible): Penicillin G 200,000-300,000 U/kg/day IV divided every 4 hours, or Ceftriaxone 100 mg/kg/day IV divided every 12 hours 2

Urinary Tract Infections

Complicated UTI (Carbapenem-Resistant Enterobacterales)

• Ceftazidime-avibactam 2.5 g IV every 8 hours for 5-7 days 2
• Alternative: Meropenem-vaborbactam 4 g IV every 8 hours, or Aminoglycosides (Gentamicin 5-7 mg/kg IV daily or Amikacin 15 mg/kg IV daily) 2

VRE UTI

• Complicated: Linezolid 600 mg IV every 12 hours for 5-7 days 2
• Uncomplicated: Fosfomycin 3 g PO single dose, or Nitrofurantoin 100 mg PO 4 times daily for 3-7 days 2

Animal/Human Bites

Amoxicillin-clavulanate 875/125 mg PO every 12 hours is the oral agent of choice 2

• Parenteral: Ampicillin-sulbactam 1.5-3 g IV every 6-8 hours, or Piperacillin-tazobactam 3.375 g IV every 6-8 hours 2
• Alternative: Doxycycline 100 mg PO every 12 hours (excellent for Pasteurella) 2

Multidrug-Resistant Organisms

Pan-Resistant Staphylococcus

Vancomycin 30-60 mg/kg/day IV divided (with 25-30 mg/kg loading dose if seriously ill) PLUS Rifampin 600 mg daily or 300-450 mg twice daily 3

• Critical pitfall: Never use rifampin as monotherapy—resistance emerges within 48-72 hours 3
• Alternative when vancomycin MIC >1 mg/L: High-dose Daptomycin 8-10 mg/kg IV daily PLUS Rifampin 3

Carbapenem-Resistant Enterobacterales (CRE)

• Bloodstream: Ceftazidime-avibactam 2.5 g IV every 8 hours for 7-14 days 2
• Alternative: Polymyxin-based combinations: Colistin 5 mg CBA/kg IV loading, then 2.5 mg CBA × (1.5 × CrCl + 30) IV every 12 hours PLUS Tigecycline 100 mg IV loading, then 50 mg IV every 12 hours 2

Key Dosing Principles

Aminoglycosides should be dosed once daily based on lean body weight: Gentamicin/Tobramycin 5-7 mg/kg IV every 24 hours, Amikacin 15-20 mg/kg IV every 24 hours, with serum monitoring for individualization 2

Vancomycin requires a loading dose of 25-30 mg/kg in seriously ill patients, followed by 30-60 mg/kg/day divided every 6-12 hours, targeting trough levels of 15-20 mcg/mL 2, 3

Amoxicillin-clavulanate should be taken at the start of meals to enhance clavulanate absorption and minimize gastrointestinal intolerance 1

The every-12-hour regimen of amoxicillin-clavulanate (875/125 mg for adults, 45 mg/kg/day for children) is preferred over every-8-hour dosing because it significantly reduces diarrhea incidence (14% vs 34%) while maintaining equivalent efficacy 1