High-performance liquid chromatographic determination of total thiamine in human plasma for oral bioavailability studies.

A high-performance liquid chromatographic method for the determination of total thiamine in plasma was developed for a relative bioavailability comparison of two oral thiamine preparations. After separation of thiamine mono- and diphosphates with the phosphatase enzyme, the total thiamine was subjected to reversed-phase high-performance liquid chromatography, postcolumn oxidized to thiochrome with K3[Fe(CN)6], and detected by fluorescence. In the bioavailability study, 16 human subjects were put on a low-thiamine diet for 3 days. On the 2nd and 3rd days, 14 blood samples per subject and day were taken at the same times each day. Drug administration did not take place until the 3rd day. After deduction of the native concentrations of total thiamine detected on the 2nd day (mean value of approximately 7 ng/mL), the post-treatment pharmacokinetic parameters were determined (two different preparations, each with 200 mg of thiamine.HCl).