What are the oral counterparts, including doses and frequency, of intravenous (IV) antibiotics?

Oral Counterparts of IV Antibiotics: Doses and Frequencies

For many intravenous (IV) antibiotics, there are oral equivalents that can be used when patients achieve clinical stability, with similar bioavailability and efficacy for most infections. 1, 2

Common IV to Oral Antibiotic Conversions

Antibiotics with High Bioavailability (≥90%)

These medications achieve comparable serum/tissue concentrations when given orally as their IV counterparts:

• Linezolid

  • IV: 600 mg every 12 hours
  • Oral: 600 mg every 12 hours 3

• Trimethoprim-Sulfamethoxazole (TMP-SMX)

  • IV: Based on TMP component 8-10 mg/kg/day divided every 8-12 hours
  • Oral: 160-320 mg TMP/800-1600 mg SMX every 12 hours 3

• Metronidazole

  • IV: 500 mg every 8 hours
  • Oral: 500 mg every 8 hours 3, 2

• Fluoroquinolones

  • Levofloxacin
    • IV: 750 mg daily
    • Oral: 750 mg daily 4, 2
  • Ciprofloxacin
    • IV: 400 mg every 12 hours
    • Oral: 750 mg every 12 hours 3

• Doxycycline/Minocycline

  • IV: 100 mg every 12 hours
  • Oral: 100 mg every 12 hours 3, 2

Antibiotics with Moderate Bioavailability

These require dose adjustments when switching from IV to oral:

• Penicillins

  • Ampicillin
    • IV: 200-300 mg/kg/day divided every 4-6 hours (up to 12g daily)
    • Oral: Amoxicillin 500-875 mg every 8 hours 3

• Cephalosporins

  • Ceftriaxone
    • IV: 1-2g every 24 hours or 50-100 mg/kg/day divided every 12-24 hours
    • Oral: Cefuroxime 500 mg twice daily or cefpodoxime 200 mg twice daily 3
  • Cefazolin
    • IV: 1-2g every 8 hours or 100 mg/kg/day divided every 8 hours
    • Oral: Cephalexin 500 mg every 6 hours 3

• Clindamycin

  • IV: 600-900 mg every 8 hours
  • Oral: 300-450 mg every 6-8 hours 3, 2

Special Considerations

Switching Criteria

Switch from IV to oral therapy when:

• Patient is hemodynamically stable
• Patient is afebrile for 24-48 hours
• Patient can tolerate oral medications
• No evidence of gastrointestinal malabsorption 2, 5

Infections Suitable for Early IV to Oral Switch

• Community-acquired pneumonia (after 3-5 days)
• Complicated urinary tract infections
• Skin and soft tissue infections
• Uncomplicated bacteremia 5, 6

Infections Requiring Extended IV Therapy

• Complicated bacteremia
• Infective endocarditis
• Bone and joint infections (though recent evidence suggests earlier switch may be possible) 3, 5

Cautions and Contraindications

• Not appropriate for:

  • Critically ill patients
  • Patients with malabsorption syndromes
  • Patients with severe sepsis/septic shock
  • Patients unable to take oral medications 2, 5

• Vancomycin considerations:

  • No direct oral equivalent for systemic infections
  • Linezolid may be used as oral alternative for MRSA infections 3

• Carbapenem considerations:

  • No direct oral equivalent
  • May require combination oral therapy to provide equivalent coverage 2

Benefits of IV to Oral Switch

• Reduced risk of catheter-related complications
• Decreased hospital length of stay
• Lower healthcare costs
• Improved patient comfort and mobility 1, 2, 6

Early transition to oral antibiotics has been shown to be non-inferior to continued IV therapy for many infections, including certain types of bacteremia, when patients have achieved clinical stability 6, 7.