Summary.A sensitive validated high-performance liquid-chromatographic method for analysis of cilostazol in human plasma (in vitro) has been developed, and it was applied to determine pharmacokinetics of cilostazol in male albino rabbit. Cilostazol was extracted from human plasma (in vitro) by acetonitrile, and efficient chromatographic elution was achieved on a C18 column (250 × 4.60 mm i.d., 0.5 µm particle size) with an isocratic mobile phase [acetonitrile-50 mM acetate buffer (pH 5.0, glacial acetic acid)-water (50:20:30)] at flow rate of 1.5 mL min −1 . Quantification was carried out by photo-diode array (PDA) detection at 248 nm. The linearity of the method was excellent over the range 0.2-2 μg mL −1 with low limits of detection (0.005 μg mL −1 ) and quantification (0.05 μg mL −1 ). The extraction recovery of the drug from plasma was consistently good (73.45-78.64%), with low relative standard deviation (0.44-1.65%). Robustness studies confirmed that peak area was unaffected by small changes in temperature, mobile phase (composition and pH). The maximum concentration (C max ) in rabbit (in vivo) was determined 1.620 μg mL −1 at t max (0.51 h) with 0.63% RSD by validated bioanalytical method.

Background: Levothyroxine is a synthetic thyroid hormone that is chemically identical to Thyroxine (T4), which is secreted by the follicular cells of the thyroid gland. Levothyroxine is used to treat deficiency of thyroid hormone and to prevent the recurrence of thyroid cancer. Levothyroxine is present endogenously in human body. Method: It requires treated matrix for the preparation of calibration curve standard and quality control samples. The method was developed using LC-MS/MS and validated in human charcoal stripped serum. Charcoal stripped matrix was used for the preparation of Calibration curve standards and Quality control samples. Method involves Solid-Phase Extraction technique. Levothyroxine D3 used as an internal standard (ISTD). Result: Chromatographic separation was achieved using reversed phase analytical column Gemini NX-C18 110Å, 3µm (50x3.6) mm. Mobile phase consisted of acetonitrile and water in a ratio of 70:30 with 150µL of formic acid in 1000 mL of mobile phase. Mobile phase achieved shorter run-time of 0.9 minute due to use of Ultra-high performance liquid chromatography (UHPLC). Positive electro-spray ionization technique detected MRM ion pair transitions 777.60→731.65 for Levothyroxine and 780.70→734.6 for Levothyroxine- D3 (ISTD) were used. AB SCIEX Triple Quad™ API-4000 LC-MS/MS system and the bioanalytical method with 10ng/mL as limit of quantification has been applied successfully to pharmacokinetics studies. Conclusion: Chromatographic separation was achieved using reversed phase analytical column Gemini NX-C18 110Å, 3µm (50x3.6) mm. Mobile phase consisted of acetonitrile and water in a ratio of 70:30 with 150µL of formic acid in 1000 mL of mobile phase. Mobile phase achieved shorter run-time of 0.9 minute due to use of Ultra-high performance liquid chromatography (UHPLC). Positive electro-spray ionization technique detected MRM ion pair transitions 777.60→731.65 for Levothyroxine and 780.70→734.6 for Levothyroxine- D3 (ISTD) were used. AB SCIEX Triple Quad™ API-4000 LC-MS/MS system and the bioanalytical method with 10ng/mL as limit of quantification has been applied successfully to pharmacokinetics studies.