DETERMINATION OF FK506 IN RAT BLOOD BY LC-MS/MS AND EFFECT OF SILYMARIN ON ITS PHARMACOKINETICS.

A simple and specific LC-MS/MS method for the determination of FK506 in blood was developed, validated, and successfully applied in pharmacokinetic studies of the effect of silymarin on FK506 in rats. Blood samples were extracted by liquid-liguid extraction with methyl tert-butyl ether and separated on an Eclipse plus-C18 column (150 × 2.1 mm, 3.5 µm) with the mobile phase of acetonitrile-10 mM ammonium acetate buffer solution (80:20, v/v). FK506 was detected without interference in the multiple-reaction monitoring mode with positive electrospray ionization. Good linearity was achieved over a range of 2.0–200 ng mL−1. The intra- and inter-day precisions were less than 13.5 % for all concentrations of quality control samples. The recoveries of FK506 were 74.2–85.3 %. Although the mean Cmax and AUC0 − ∞ of FK506 were increased to some extent, there was no significant difference in the pharmacokinetic profile of FK506 after oral administration to rats in the presence and absence of silymarin (200 mg kg−1, 2 times/d for 14 d). [ABSTRACT FROM AUTHOR]