What are the typical dosages of antibiotics for adults?

Adult Antibiotic Dosing Guidelines

For adult patients requiring antibiotic therapy, dosing should follow standardized regimens based on the specific antibiotic class, with adjustments made for infection severity, site of infection, and patient factors.

Common Antibiotic Classes and Standard Adult Dosages

β-lactam/β-lactamase Inhibitor Combinations

• Piperacillin-tazobactam: 3.375 g IV every 6 hours (can increase to 4.5 g every 6 hours for Pseudomonas infections) 1
• Amoxicillin-clavulanate:
  • 875/125 mg PO twice daily for more severe infections
  • 500/125 mg PO every 8 hours for moderate infections 2

Carbapenems

• Ertapenem: 1 g IV every 24 hours
• Imipenem/cilastatin: 500 mg IV every 6 hours or 1 g every 8 hours
• Meropenem: 1 g IV every 8 hours 1

Cephalosporins

• Cefazolin: 1-2 g IV every 8 hours
• Cefepime: 2 g IV every 8-12 hours
• Ceftriaxone: 1-2 g IV every 12-24 hours
• Cefuroxime: 1.5 g IV every 8 hours or 500 mg PO twice daily 1

Macrolides

• Azithromycin:
  • 500 mg PO on day 1, then 250 mg once daily for 4 days
  • Alternative: 500 mg PO once daily for 3 days 3
  • For certain infections (e.g., chlamydia): 1 g PO as a single dose 4

Tetracyclines

• Doxycycline: 100 mg PO twice daily (200 mg on first day, then 100 mg daily for maintenance) 5

Fluoroquinolones

• Ciprofloxacin: 400 mg IV every 12 hours or 500-750 mg PO twice daily
• Levofloxacin: 750 mg IV/PO every 24 hours 1

Other Important Antibiotics

• Vancomycin: 15-20 mg/kg IV every 8-12 hours (based on total body weight, with serum level monitoring) 1
• Clindamycin: 600 mg IV every 8 hours or 300-450 mg PO three times daily 1
• Metronidazole: 500 mg IV/PO every 8-12 hours 1
• Aminoglycosides (e.g., gentamicin): 5-7 mg/kg IV once daily (with drug level monitoring) 1

Infection-Specific Dosing Considerations

Skin and Soft Tissue Infections

• MSSA infections: Dicloxacillin 500 mg PO four times daily or cephalexin 500 mg PO four times daily
• MRSA infections: Vancomycin 30 mg/kg/day IV in 2 divided doses or linezolid 600 mg IV/PO every 12 hours 1

Intra-abdominal Infections

• Duration: Limit antimicrobial therapy to 4-7 days unless source control is difficult to achieve 1
• Regimen selection: Based on severity, with broader coverage for healthcare-associated infections 1

Babesiosis

• First-line: Atovaquone 750 mg PO every 12 hours plus azithromycin 500-1000 mg PO on day 1, then 250 mg once daily
• Severe disease: Clindamycin 300-600 mg IV every 6 hours (or 600 mg PO every 8 hours) plus quinine 650 mg PO every 6-8 hours 1

Important Clinical Considerations

Dosage Adjustments

• Renal impairment: Dose adjustments required for many antibiotics, particularly aminoglycosides, vancomycin, and some β-lactams
• Hepatic impairment: May require dose adjustments for certain antibiotics metabolized by the liver

Duration of Therapy

• Uncomplicated infections: Often 5-7 days is sufficient
• Complicated infections: May require 10-14 days or longer based on clinical response
• Specific infections: Follow guideline-recommended durations (e.g., 7-10 days for babesiosis) 1

Monitoring

• Clinical response: Assess within 48-72 hours of initiating therapy
• Drug levels: Monitor for vancomycin, aminoglycosides
• Adverse effects: Monitor for gastrointestinal symptoms, allergic reactions, and organ toxicity

Common Pitfalls to Avoid

• Underdosing: Particularly problematic in severe infections or with resistant organisms
• Excessive duration: Extending antibiotics beyond recommended duration increases resistance risk without improving outcomes
• Ignoring culture results: Adjust therapy based on culture and susceptibility when available
• Failing to consider local resistance patterns: Local antibiograms should guide empiric therapy choices

Remember that these dosages are for adults with normal renal and hepatic function. Always consider patient-specific factors such as allergies, comorbidities, and potential drug interactions when selecting antibiotic regimens.