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Tolterodine is a nonselective muscarinic antagonist that is indicated for the overactive urinary bladder and other urinary difficulties. We developed and validated a simple, rapid and sensitive high-performance liquid chromatography analytical method utilizing tandem mass spectrometry (LC-MS/MS) for the quantitation of tolterodine and its major metabolites, 5-hydroxymethyltolterodine (5-HMT) and N-dealkyltolterodine (NDT), in human plasma. After liquid-liquid extraction with methyl t-butyl ether, chromatographic separation of the three analytes was achieved using a reversed-phase Luna Phenyl-hexyl column (100 × 2.0 mm, 3 μm particles) with a mobile phase of 10 mM ammonium formate buffer (pH 3.5)-methanol (10:90, v/v) and quantified by MS/MS detection in electrospray ionization (ESI) positive ion mode. The retention time of tolterodine, 5-HMT, NDT, and internal standard (IS) were 1.4, 1.24, 1.33, and 1.26 min, respectively. The calibration curves were linear over a range of 0.025-10 ng/ml for tolterodine and 5-HMT, and 0.05-10 ng/ml for NDT. The lower limit of quantifications using 200 μl of human plasma was 0.025 ng/ml for tolterodine and 5-HMT, and 0.05 ng/ml for NDT. The mean accuracy and precision for intra- and inter-run validation of tolterodine, 5-HMT, and NDT were all within acceptable limits. These results showed that a simple, rapid and sensitive LC-MS/MS method for the quantification of tolterodine and its major metabolites in human plasma was developed. This method was successfully applied to a pharmacokinetic study in humans.

Zolpidem (ZPD) is widely described for the short-term treatment of insomnia. We have developed and validated a simple and rapid liquid chromatography analytical method using tandem mass spectrometry (LC-MS/MS) for the quantification of ZPD in human plasma. Using dibucaine as an internal standard (IS), the analyte was extracted with methyl t-butyl ether (MTBE). Chromatographic separation of ZPD was performed on a reversed-phase Luna C18 column (50 mm × 2.0 mm i.d., 5 μm particles) with a mobile phase of 10mM ammonium formate buffer (pH 3.0)-methanol (15:85, v/v) at a flow rate of 250 μm/min. The total run-time was 2.5 min and the retention times of ZPD and IS were 0.66 and 0.74 min, respectively. The mass-to-charge transition monitored for quantification of ZPD and IS was 308.2→235.2 and 344.0→271.0, respectively. The lower limit of quantification (LLOQ) using 100 μL of human plasma was 0.05 ng/mL and the calibration curves were linear over a range of 0.05-200 ng/mL (r(2)>0.9964). The mean accuracy and precision for intra- and inter-run validation of ZPD were within acceptable limits. In the present LC-MS/MS method, we showed improved sensitivity for quantification of the ZPD in human plasma using lower volume of plasma compared with previously described analytical methods for ZPD. This validated method was successfully applied to a pharmacokinetic study in humans., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Flurbiprofen (FLB) is one of the phenylalkanoic acid derivatives of non-steroidal anti-inflammatory drugs used for the management of pain and inflammation in patients with arthritis. We developed and validated a rapid and sensitive high-performance liquid chromatography analytical method utilizing tandem mass spectrometry (HPLC-MS/MS) for the simultaneous determination of FLB and its major metabolite, 4'-hydroxyflurbiprofen (4'-OH-FLB), in human plasma. Probenecid was used as an internal standard (IS). After liquid-liquid extraction with methyl t-butyl ether, chromatographic separation of the two analytes was achieved using a reversed-phase Luna C18 column (2.0mm×50mm, 5μm particles) with a mobile phase of 10mM ammonium formate buffer (pH 3.5)-methanol (15:85, v/v) and quantified by MS/MS detection in ESI negative ion mode. The flow rate of the mobile phase was 250μl/min and the retention times of FLB, 4'-OH-FLB, and IS were 1.1, 0.8, and 0.9min, respectively. The calibration curves were linear over a range of 0.01-10μg/ml for FLB and 0.01-1μg/ml for 4'-OH-FLB. The lower limit of quantifications using 100μl of human plasma was 0.01μg/ml for both analytes. The mean accuracy and precision for intra- and inter-run validation of FLB and 4'-OH-FLB were all within acceptable limits. The present HPLC-MS/MS method showed improved sensitivity for quantification of the FLB and its major metabolite in human plasma compared with previously described analytical methods. The validated method was successfully applied to a pharmacokinetic study in humans., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Tamsulosin, a selective α₁-adrenoceptor antagonist, is used for the treatment of benign prostatic hyperplasia (BPH). We developed and validated a rapid, sensitive, and simplified liquid chromatography analytical method utilizing tandem mass spectrometry (LC-MS/MS) for the determination of tamsulosin in human plasma. After liquid-liquid extraction with methyl t-butyl ether, chromatographic separation of tamsulosin was achieved using a reversed-phase Luna C₁₈ column (2.0 mm × 50 mm, 5 μm particles) with a mobile phase of 10 mM ammonium formate buffer (pH 3.5)-methanol (25:75, v/v) and quantified by MS/MS detection in ESI positive ion mode. The flow rate of the mobile phase was 200 μL/min and the retention times of tamsulosin and the internal standard (IS, diphenhydramine) were 0.8 and 0.9 min, respectively. The calibration curves were linear over a range of 0.01-20 ng/mL (r>0.999). The lower limit of quantification using 500 μL of human plasma was 0.01 ng/mL. The mean accuracy and precision for intra- and inter-day validation of tamsulosin were both within acceptable limits. The present LC-MS/MS method showed improved sensitivity for quantification of tamsulosin in human plasma compared with previously described analytical methods. The validated method was successfully applied to a pharmacokinetic study in humans., (Copyright © 2012 Elsevier B.V. All rights reserved.)