A highly sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the determination of tadalafil (TAD) in human plasma. TAD and its deuterated internal standard (IS), tadalafil-d3, were extracted from 200 µL plasma using Phenomenex Strata-X-C 33 µ extraction cartridges. Chromatographic analysis was carried out on Synergi™ Hydro-RP C18 (100 mm × 4.6 mm, 4 µm) column with a mobile phase consisting of methanol and 10 mM ammonium formate, pH 4.0 (90:10, v/v), delivered at a flow rate of 0.9 mL/min. Quantitation of the protonated analyte was done on a triple quadrupole mass spectrometer using multiple reaction monitoring via electrospray ionization. The precursor to product ions transitions monitored for TAD and TAD-d3 were m/z 390.3 → 268.2 and m/z 393.1 → 271.2, respectively. The calibration curve was linear over the concentration range of 0.50–500 ng/mL with correlation coefficient, r2 ≥ 0.9994. Acceptable intra-batch and inter-batch precision (≤ 3.7%) and accuracy (97.8% to 104.1%) were obtained at five concentration levels. The recovery of TAD from spiked plasma was highly precise and quantitative (98.95% to 100.61%). Further, the effect of endogenous matrix components was minimal. TAD was found to be stable under different storage conditions in human plasma and also in whole blood samples. The validated method was successfully used to determine TAD plasma concentration in a bioequivalence study with 20 mg TAD tablets in 24 healthy volunteers. Method performance was evaluated by reanalyzing 115 study samples.

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A rapid, specific and sensitive ultra-performance liquid chromatography tandem mass spectrometry method was developed for the determination of fenofibric acid in human plasma. The method involves simple, one-step liquid-liquid extraction procedure coupled with an Acquity UPLC(TM) BEH C(18) column (50 x 2.1 mm, i.d., 1.7 microm) with isocratic elution at a flow-rate of 0.2 mL/min and mefenamic acid was used as the internal standard. The Quattro Premier XE mass spectrometry was operated under the multiple reaction-monitoring mode using the electrospray ionization technique. Using 250 microL plasma, the methods were validated over the concentration rang 0.05-7.129 microg/mL, with a lower limit of quantification of 0.05 microg/mL. The intra- and inter-day precision and accuracy were within 9.3%. The recovery was 66.7% and 52.6% for fenofibric acid, and mefenamic acid, respectively. Total run time was 1.8 min only for each sample, which makes it possible to analyze more than 350 samples per day.

A rapid, sensitive and rugged solid-phase extraction ultraperformance liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed for determination of oseltamivir phosphate (OP) and oseltamivir carboxylate (OC) in human plasma. The procedure for sample preparation includes a simple SPE extraction procedure coupled with a Chromatopack C(18) column (50 × 3.0 mm, i.d., 3.0 µm) with isocratic elution at a flow-rate of 0.600 mL /min and acyclovir was used as the internal standard. The analysis was performed on a triple-quadrupole tandem mass spectrometer by multiple reaction monitoring mode via electrospray ionization. Using 500 µL plasma, the methods were validated over the concentration ranges 0.92-745.98 and 5.22-497.49 ng/mL for OP and OC, with a lower limit of quantification of 0.92 and 5.22 ng/mL. The intra- and inter-day precision and accuracy of the quality control samples were within 10.1%. The recovery was 68.72, 70.66 and 71.59% for OP, OC and IS, respectively. Total run time was only 1.0 min. The method was highly reproducible with excellent chromatography properties.

A rapid, specific and sensitive liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed for the determination of penciclovir in human plasma. The method involved simple, one-step SPE procedure coupled with a C(18) , 75 × 4.mm, 3 µm column with a flow-rate of 0.5 mL/min, and acyclovir was used as the internal standard. The Quattro Micro mass spectrometry was operated under the multiple reaction-monitoring mode using the electrospray ionization technique. Using 250 µL plasma, the methods were validated over the concentration range 52.555-6626.181 ng/mL, with a lower limit of quantification of 52.55 ng/mL. The intra- and inter-day precision and accuracy values were found to be within the assay variability limits as per the FDA guidelines. The developed assay method was applied to a clinical pharmacokinetic study in human volunteers.