Vitamin C pharmacokinetics differ significantly between oral and intravenous administration. A study in 17 healthy volunteers found that intravenous vitamin C produced plasma concentrations 30-70 times higher than the maximum tolerated oral dose. Intravenous administration achieved peak plasma concentrations of 885 ± 201.2 μmol/L, compared to 134.8 ± 20.6 μmol/L for oral administration of 1.25 g. Pharmacokinetic modeling predicted that a 50-g intravenous dose would result in peak plasma concentrations of 13,400 μmol/L, while oral doses of 3 g every 4 hours produced 220 μmol/L. Intravenous administration also resulted in urine concentrations 140 times higher than oral doses. Oral vitamin C concentrations are tightly controlled, with steady-state values around 70-85 μmol/L. Intravenous administration bypasses this control, achieving much higher plasma and urine concentrations. These higher concentrations may have antitumor activity, as in vitro studies show vitamin C is toxic to cancer cells at concentrations above 1000 μmol/L. However, clinical trials have shown no benefit from oral vitamin C at 10 g/day, while intravenous administration was not tested in these trials. The study highlights the importance of route of administration in determining vitamin C concentrations. While oral vitamin C is safe and effective for general health, intravenous administration may offer higher concentrations that could be beneficial in cancer treatment. However, the role of vitamin C in cancer treatment should be re-evaluated due to the lack of evidence for clinical benefit from oral dosing. The study also notes that vitamin C supplements do not significantly increase plasma concentrations beyond those from food, suggesting that dietary intake may be more effective for general health. The findings emphasize the need for further research into the potential of intravenous vitamin C in cancer treatment.Vitamin C pharmacokinetics differ significantly between oral and intravenous administration. A study in 17 healthy volunteers found that intravenous vitamin C produced plasma concentrations 30-70 times higher than the maximum tolerated oral dose. Intravenous administration achieved peak plasma concentrations of 885 ± 201.2 μmol/L, compared to 134.8 ± 20.6 μmol/L for oral administration of 1.25 g. Pharmacokinetic modeling predicted that a 50-g intravenous dose would result in peak plasma concentrations of 13,400 μmol/L, while oral doses of 3 g every 4 hours produced 220 μmol/L. Intravenous administration also resulted in urine concentrations 140 times higher than oral doses. Oral vitamin C concentrations are tightly controlled, with steady-state values around 70-85 μmol/L. Intravenous administration bypasses this control, achieving much higher plasma and urine concentrations. These higher concentrations may have antitumor activity, as in vitro studies show vitamin C is toxic to cancer cells at concentrations above 1000 μmol/L. However, clinical trials have shown no benefit from oral vitamin C at 10 g/day, while intravenous administration was not tested in these trials. The study highlights the importance of route of administration in determining vitamin C concentrations. While oral vitamin C is safe and effective for general health, intravenous administration may offer higher concentrations that could be beneficial in cancer treatment. However, the role of vitamin C in cancer treatment should be re-evaluated due to the lack of evidence for clinical benefit from oral dosing. The study also notes that vitamin C supplements do not significantly increase plasma concentrations beyond those from food, suggesting that dietary intake may be more effective for general health. The findings emphasize the need for further research into the potential of intravenous vitamin C in cancer treatment.