Vitamin C pharmacokinetics: implications for oral and intravenous use

Padayatty SJ, Sun H, Wang Y, Riordan HD, Hewitt SM, Katz A, Wesley RA, Levine M · Annals of Internal Medicine

Puts a hard ceiling on what any oral dose can achieve. A 1.25 g oral dose produced a mean peak plasma concentration of 134.8 µmol/L; the same dose intravenously produced 885 µmol/L. Modelling the maximum tolerated oral regimen — 3 g every four hours — predicts a peak of only 220 µmol/L. Oral vitamin C is tightly controlled by absorption and renal clearance, so beyond about a gram the body, not the label, decides the exposure.

Population

Healthy hospitalized volunteers

Intervention

Oral and intravenous vitamin C from 0.015 to 1.25 g, with pharmacokinetic modelling out to 100 g

Limitations

Seventeen healthy volunteers, and the high-dose figures are modelled rather than measured. Written to address intravenous vitamin C in cancer, so the joint-relevant reading is a secondary use of the data. No tissue or clinical endpoint.