What is the Difference in Bioavailability of Oral and Intravenous Vitamin C?

There is a large variation in the bioavailability of oral and intravenous Vitamin C. This is because the transporting capability of the intestinal sodium ascorbate co-transporter, SVCT1, a surface glycoprotein that facilitates Vitamin C absorption, ¹ is limited and achieves maximal saturation around oral doses of 500-1000 mg. ² Intravenous administration of Vitamin C bypasses the limitations of SVCT1-induced bioavailability.

In a dose concentration and pharmacokinetic modeling study of healthy hospitalized volunteers, consumption of 5-9 servings of fruits and vegetables daily resulted in steady state Vitamin C plasma concentrations of 80 µmol/L or less and peak values did not exceed 220 µmol/L even after maximum oral administration of 3 grams, six times daily. In this same study, at a dose of 100 grams, intravenous administration of Vitamin C achieved peak plasma concentrations as high as 15,000 µmol/L, a plasma concentration 70 times higher than oral administration. ³

In another Vitamin C pharmacokinetics dosing study in healthy volunteers, the bioavailability of intravenous ascorbic acid was higher than oral ascorbic acid at single doses of 500 and 1250 mg but not at a dose of 200 mg. ² Doses of ascorbic acid injection higher than 200 mg daily have not been approved by the US FDA.

Savini, I., Rossi, A., Pierro, C. et al. SVCT1 and SVCT2: key proteins for vitamin C uptake. Amino Acids 34, 347–355 (2008), https://doi.org/10.1007/s00726-007-0555-7.
Levine, M., Conry-Cantilena, C., Wang, Y. et al. Vitamin C pharmacokinetics in healthy volunteers: Evidence for a recommended dietary allowance. Proc. Natl. Acad. Sci. USA 93:3704-3709 (1996), Vitamin C pharmacokinetics in healthy volunteers: evidence for a recommended dietary allowance. (nih.gov).
Padayatty, S., Sun, H., Wang, Y. et al. Vitamin C Pharmacokinetics: Implications for Oral and Intravenous Use. Ann Intern Med 140: 533-537 (2004).

Indication & Important Safety Information

ASCOR^® is vitamin C indicated for the short term (up to 1 week) treatment of scurvy in adult and pediatric patients age 5 months and older for whom oral administration is not possible, insufficient or contraindicated.

Limitations of Use:
ASCOR^® is not indicated for treatment of vitamin C deficiency that is not associated with signs and symptoms of scurvy.

Important Safety Information

Contraindications: None.

Administration site reactions include pain and swelling.

ASCOR^® should not be rapidly administered. Rapid intravenous administration (>250 mg/minute) of ASCOR^® may cause temporary faintness or nausea, lethargy, flushing, dizziness, and headache.

Acute and chronic oxalate nephropathy have occurred with prolonged administration of high doses of ascorbic acid. ASCOR^® is not indicated for prolonged administration. The maximum recommended duration is one week.

In patients with glucose-6-phosphate dehydrogenase deficiency severe hemolysis has occurred.

Ascorbic acid may interfere with laboratory tests based on oxidation-reduction reactions, including blood and urine glucose testing, nitrite and bilirubin levels, and leucocyte count testing. If possible, laboratory tests based on oxidation-reduction reactions should be delayed until 24 hours after infusion of ASCOR^®.

Please see accompanying Full Prescribing Information for ASCOR^®.