[Determination of plasma drug concentration and bioavailability of indomethacin controlled release capsule by high...

A simple, rapid, sensitive and accurate reversed-phase high performance liquid chromatographic (RP-HPLC) method for the determination of indomethacin in plasma is established. To 1 mL of plasma were added 200 microL of amobarbitone solution (internal standard; 1 g/L), 100 microL of phosphate buffer solution (pH 7.0), 100-150 mg of sodium chloride and 2.5 mL of ethyl acetate. The mixture was vortex-mixed for 10 min and centrifuged at 3000 r/min for 5 min. The organic layer was evaporated to dryness at 50 degrees C on water-bath and the residue was dissolved in methanol (100 microL). A 20 microL portion of the resulting solution was analysed by HPLC on a column (25 cm x 4.6 mm) of micro-Bondapak C18 (10 microm) with 76% methanol in 0.035 mol/L phosphoric acid (pH 5.5) aq-solution as mobile phase (1 mL/min) and UV detection at 260 nm. The column temperature was 30 degrees C. Within the range of 0.125-50 mg/L of indomethacin there was a good linearity (r = 0.9996). The mean recovery of indomethacin was 100.4%. The detectable limit was 62.5 microg/L (S/N = 3:1). The within day and day-to-day RSD were less than 5% at three drug levels. This method has been used to determine plasma drug concentration and bioavailability of indomethacin controlled release capsule for healthy volunteers.