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A method for bioanalysis of pentoxifylline in human plasma was developed using liquid chromatography–tandem mass spectrometry, which is simple, specific, and sensitive. Pentoxifylline D5 was used as the internal standard. Employing only 100 µl of human plasma, processing was done with solid-phase extraction technique. The analyte and the internal standard were separated from endogenous components on Ace phenyl column using a mixture of 5 mM ammonium acetate buffer and high performance liquid chromatography grade acetonitrile (60:40, v/v) as mobile phase at a flow rate of 1 ml/min. The linearity of the method was in the range of 3–1200 ng/ml with r2 > 0.99. Positive ion MRM mode was used for the detection of the analyte and the internal standard. The method was validated as per the US Food and Drug Administration guidelines and the results were within the acceptance limits. The proposed method was applied for comparative pharmacokinetic study of pentoxifylline after oral administration of 400 and 600 mg tablets to South Indian male subjects under fed conditions.

A selective, sensitive and high-throughput liquid chromatography-tandem mass spectrometry bioanalytical method has been developed for the estimation of cycloserine in human plasma, employing cytosine as the internal standard. The extraction of the analyte was facilitated by solid-phase extraction using 100 μL of human plasma.The separation was carried out on a BDS Hypersil C 18 (150 × 4.6 mm, 5 μm) column using a mixture of 0.2% formic acid in HPLC-grade water, methanol and acetonitrile (70:15:15, v/v/v) as mobile phase at a flow rate of 1.0 mL/min. The method was linear over the range of 0.20-20 μg/mL with r 2 > 0.99. Complete validation of the method was performed as per US Food and Drug Administration guidelines and the results met acceptance criteria. Applying the present method, the clinical pharmacokinetics of cycloserine following oral administration of 250 mg cycloserine was studied under fasting conditions. Assay reproducibility was also verified by incurred sample reanalysis.

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