Application of a Liquid Chromatography: Tandem Mass Spectrometry Based Method to Determine Plasma Cycloserine Concentrations in Indian MDR-TB Patients—A Pilot Study

Cycloserine is widely used for treatment of multidrug-resistant tuberculosis (MDR-TB) as a component of multidrug treatment regimens. There are limited reports on the pharmacokinetics of cycloserine in MDR-TB patients, especially from a high TB burden country like India. Despite longstanding clinical use, cycloserine has a narrow therapeutic index and its neuropsychiatric side effects warrant therapeutic drug monitoring to ensure safe and effective dosing. We aimed to develop a high-performance liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS)-based method for analysis of cycloserine in human plasma collected from MDR-TB patients and describe its pharmacokinetics in a pilot study. The method was developed on a reverse phase column using gradient mode and quantitated on the mass spectrometer using electron spray ionisation in a positive mode. The method linearity was obtained between 0.782 to 50 mg/L and all other method validation parameters passed the acceptability criteria as per the U.S. FDA Bioanalytical method validation guidelines. For the pharmacokinetic analysis, whole blood was collected at 6 time points over 8-h following observed ingestion after achieving steady state. The median maximum concentration (Cmax), observed 2 h after ingestion was found to be 16.0 (interquartile range, 11.7–20.8) mg/L and the area under curve until the 8-hour period was 121.17 mg.h/L. This LC-MS/MS method provides a simple, robust method to quantify cycloserine concentrations in human plasma and has been successfully applied for pilot pharmacokinetic study which may support dose optimization.