Pharmacology: Pharmacokinetics: Vitamin C is readily absorbed from the gastrointestinal tract and is widely distributed in the body tissues. Plasma concentrations of Vitamin C rise as the dose of about 90 to 150 mg daily. Body stores of Vitamin C in health are about 1.5 g although more may be stored at intakes above 200 mg daily. The concentration is higher in leucocytes and platelets than in erythrocytes and plasma. In deficiency states the concentration in leucocytes declines later at a slower rate and has been considered to be better criterion for the evaluation of deficiency than the concentration in plasma.
Distribution: Widely distributed in body tissues with about 25% bound to plasma proteins. Large amounts are present in leucocytes and platelets. Ascorbic acid crosses the placenta.
Metabolism: Readily oxidized to dehydroascorbic acid where some is metabolised to oxalic acid and the inactive ascorbate-2-sulphate. Metabolic turnover appears to be greater in females than males.
Excretion: Large doses are rapidly excreted in the urine when in excess of the requirements of the body and after an intravenous dose, about 40% is excreted in 8 hours, which is increased to about 70% after tissue saturation. The amount of unchanged drug is dose dependent; in women the excretion of ascorbic acid appears to vary with the stage of the menstrual cycle and it is decreased when taking oral contraceptives.