DETERMINATION OF THE IMMUNOSUPPRESSIVE DRUG TACROLIMUS IN ITS DOSAGE FORMS BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A high-performance liquid chromatographic (HPLC) method has been devel oped and validated for the determination of FK506, a new immunosuppres sant, in bulk drug samples and dosage forms. Equilibration between FK5 06 (I) and its tautomeric compounds (II and III) was accomplished ''ar tificially'' in water-dehydrated alcohol (1:1) employed as an extracti on solvent. After reaching equilibrium, separation of I, treated as th e representative of equilibrated FK506, from its related substances wa s achieved by reversed-phase HPLC on a Cls column with water-isopropyl alcohol-tetrahydrofuran (5:2:2, v/v) as the mobile phase, and detecti on at 220 nm. Component I in dosage forms could be recovered satisfact orily and determined with good precision. The calibration graph was li near over the range 2-6 mu g for I.