Oral and IV Vancomycin Are Not Interchangeable for Dosing
There is no oral dosage equivalent of 1000 mg IV vancomycin because these routes serve completely different therapeutic purposes and have fundamentally different pharmacokinetics. Oral vancomycin is not absorbed systemically and remains in the gut lumen, while IV vancomycin achieves systemic concentrations but does not reach therapeutic levels in the colon 1, 2.
Why No Equivalence Exists
Pharmacokinetic Differences
Oral vancomycin is poorly absorbed from the gastrointestinal tract (typically <1% absorption) and remains concentrated in the gut lumen, which is precisely why it is effective for treating C. difficile infection 1, 2.
IV vancomycin does not reach the colon in therapeutic concentrations and has no effect on C. difficile infection unless there is severe colonic inflammation 1.
In a prospective study of 57 patients receiving oral vancomycin 125 mg four times daily, 98% had no detectable serum vancomycin concentrations, confirming minimal systemic absorption 2.
Different Clinical Indications
For C. difficile infection (oral route):
- Standard dosing is vancomycin 125 mg orally four times daily for 10 days, regardless of what IV dose might be used for other infections 3, 4.
- For severe CDI, the same 125 mg dose is recommended 3.
- For fulminant CDI, higher oral doses of 500 mg four times daily are used 3, 4.
For systemic infections (IV route):
- IV vancomycin dosing for endocarditis ranges from 40-60 mg/kg/day divided every 6-12 hours (up to 2 g daily in adults) 3.
- For prosthetic joint infections, 15 mg/kg IV every 12 hours is recommended 3.
Critical Clinical Pitfall
Do not attempt to convert IV to oral dosing or vice versa. The route must be selected based on the infection site:
Use oral vancomycin only for C. difficile colitis at standard doses (125-500 mg four times daily) 3, 4.
Use IV vancomycin for systemic infections (bacteremia, endocarditis, osteomyelitis, etc.) with dosing based on weight, renal function, and target trough levels 3.
Special Circumstances
When Oral Vancomycin May Be Absorbed
Rare cases of systemic absorption can occur with:
- Severe intestinal inflammation 5, 6, 7
- Renal failure 5, 7
- High doses (>500 mg/day) with prolonged exposure 7
- Combined oral and rectal administration 7
Even in these cases, absorption is unpredictable and should not be relied upon for systemic therapy 2, 5, 6.
Using IV Formulation Orally
Not all IV vancomycin formulations are approved for oral administration 3. When oral capsules are unavailable, IV vancomycin can be given orally for C. difficile infection, but the dose remains 125-500 mg four times daily—not based on any IV dosing calculation 3.