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Pharmacology: Pharmacokinetics: Absorption: Ascorbic acid is readily absorbed after oral administration; however, absorption involves an active process and may be limited after very large doses. In one study in healthy individuals, only 50% of a single 1.5 g oral dose of ascorbic acid was absorbed. GI absorption of ascorbic acid may be reduced in patients with diarrhea or GI diseases.
Normal plasma concentrations of ascorbic acid are about 10-20 mcg/ml. Total body stores of ascorbic acid have been estimated to be about 1.5 g with about a 30-45 mg daily turnover. Clinical signs of scurvy usually become evident after 3-5 months of deficient ascorbic acid intake.
Distribution: Ascorbic acid is widely distributed in body tissues. About 25% of the ascorbic acid in plasma is bound to proteins.
Elimination: Ascorbic acid is reversibly oxidized to dehydroascorbic acid. Some ascorbic acid is metabolized to inactive compounds including ascorbic acid-2-sulfate and oxalic acid which are excreted in the urine. When the body is saturated with ascorbic acid and blood concentrations exceed the threshold, unchanged ascorbic acid is excreted in the urine. Ascorbic acid is removed by hemodialysis.
