The use of a nonlinear absorption model in the study of ascorbic acid bioavailability in man

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Abstract
A two‐compartment disposition model of ascorbic acid (AA) pharmacokinetics with saturable and time‐constrained intestinal absorption was developed. The model was fitted to pharmacokinetic data obtained after oral administration to nine healthy volunteers of two effervescent dosage forms differing in AA content: Celaskon 60 mg (CK60) and Celaskon 500 mg (CK500). It was demonstrated that in the case of CK500 less than 30% of the dose was absorbed as compared with CK60. Parameters of the AA nonlinear absorption kinetics were assessed by simultaneous fitting of mean concentration—time data for both doses and placebo. The relatively short duration of absorption found (3.2 h) can explain the failure of past attempts to increase the AA bioavailability using sustained‐release dosage forms. Model simulation showed that the ingestion of 60 mg with 3–4 h intervals is optimal for maximal bioavailability of AA.

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