Sensitive Ultra-performance Liquid Chromatography Tandem Mass Spectrometry Method for Determination of Cycloserine in Plasma for a Pharmacokinetics Study.

A simple and sensitive ultra-performance liquid chromatography tandem mass spectrometry method has been developed and validated for the analysis of cycloserine in patients' plasma. Using methanol, cyloserine and propranolol (internal standard (IS)) was extracted from plasma by protein precipitation procedure. The chromatographic separation was successfully achieved on Phenomenex KinetexTM PFP C18 (2.1 mm × 100 mm, 2.6 μm) reversed-phase column. Acidified with 0.1% formic acid, water and acetonitrile were used as mobile phases for gradient elution. Cycloserine and IS were detected by Xevo® TQ MS triple quadrupole tandem mass spectrometer. The transition of protonated precursor to product ion were monitored at 103 → 75 m/z and 260.2 → 183 m/z for cycloserine and IS, respectively. The lower limit of quantification was 0.01 μg/mL. The method was linear over the concentration range 0.01-50 μg/mL with average coefficient of determination of 0.9994. The within-run and between-run precision and accuracy were in the range 3.7-19.3% (RSD) and 98.7-117.3%, respectively. Processed cycloserine sample was stable for 48 hours at 8°C and after three freeze-thaw cycles. The extraction efficiency ranged between 88.7 and 91.2%. The method was successfully applied in a pharmacokinetic study for the determination of cycloserine in plasma of patients with drug-resistant tuberculosis.