Oral Counterparts of IV Antibiotics
For most serious infections, oral antibiotics with high bioavailability can effectively replace IV antibiotics after initial clinical improvement, allowing for completion of therapy without compromising patient outcomes.
Key Principles of IV to Oral Conversion
- Oral antibiotics with high bioavailability (≥90%) achieve serum/tissue concentrations comparable to IV antibiotics at the same dose 1
- IV-to-oral switch therapy is now considered standard practice for most infections after initial clinical improvement 2
- Oral therapy avoids complications associated with IV administration while reducing healthcare costs 3
Criteria for IV to Oral Switch
- Patient should be clinically stable with improvement in symptoms 4
- Patient should have functioning gastrointestinal tract with ability to absorb oral medications 5
- Not appropriate for critically ill patients or those with malabsorptive disorders 2
- Can typically be considered after 2-3 days of IV therapy when clinical improvement is observed 2
Antibiotics with Excellent Oral Bioavailability (≥90%)
- Fluoroquinolones: Levofloxacin, moxifloxacin, ciprofloxacin 6, 7
- Oxazolidinones: Linezolid, tedizolid 4
- Other high-bioavailability agents: Trimethoprim-sulfamethoxazole, metronidazole, clindamycin 5
Antibiotics with Moderate Oral Bioavailability
- Beta-lactams: Amoxicillin, amoxicillin-clavulanate, cephalexin 5
- Macrolides: Azithromycin, clarithromycin 5
- Tetracyclines: Doxycycline, minocycline 4
Common IV-to-Oral Conversions by Antibiotic Class
Beta-lactams
- IV ampicillin → Oral amoxicillin 8
- IV oxacillin/nafcillin → Oral dicloxacillin 4
- IV cefazolin → Oral cephalexin 4
- IV ceftriaxone → Oral cefuroxime or cefpodoxime 8
- IV piperacillin-tazobactam → Oral amoxicillin-clavulanate (for less severe infections) 8
Anti-MRSA Agents
- IV vancomycin → Oral linezolid, trimethoprim-sulfamethoxazole, or doxycycline 4
- IV daptomycin → Oral linezolid or tedizolid 4
- IV ceftaroline → Oral linezolid or trimethoprim-sulfamethoxazole 4
Fluoroquinolones
- IV ciprofloxacin → Oral ciprofloxacin 6
- IV levofloxacin → Oral levofloxacin 6
- IV moxifloxacin → Oral moxifloxacin 7
Other Agents
- IV clindamycin → Oral clindamycin 4
- IV metronidazole → Oral metronidazole 5
- IV trimethoprim-sulfamethoxazole → Oral trimethoprim-sulfamethoxazole 5
Special Considerations
- For antibiotics without oral formulations (e.g., carbapenems), equivalent coverage must be provided with an oral antibiotic from a different class 5
- Oral therapy is not appropriate for certain serious infections requiring prolonged IV therapy, such as endocarditis, though research is examining earlier switch options 3
- Bioavailability of oral antibiotics is near normal in all but the most critically ill patients 5
- The trend toward treating serious systemic infections entirely with oral antimicrobial therapy continues to grow as more evidence supports its efficacy 1