Application of the isoniazid assay in dried blood spots using the ultra-performance liquid chromatography-tandem mass spectrometry

Therapeutic drug monitoring (TDM) of anti-tuberculosis (TB) drugs is important for proper treatment of TB. Dried blood spots (DBSs) are widely used for TDM because of their several advantages. Rifampicin and pyrazinamide assays with DBSs have already been developed. However, isoniazid (INH) assay for capillary DBSs have not been reported because of INH instability. We developed an ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for measuring INH concentrations in venous and capillary DBSs.Each DBS was analyzed on an UPLC system. INH and internal standard (IS) concentrations were determined by multiple-reaction monitoring in positive ion mode. Analytical performances, including precision, linearity, and comparison of different types of specimens were determined. Further, the stability of INH in venous DBSs was tested.INH and IS were clearly separated in the UPLC-MS/MS system without matrix effect. Within-run precision and between-day precision were 2.68-8.02% and 2.54-5.45%, respectively. INH concentrations in venous DBS showed proportional bias compared with those in plasma (Slope: 0.8704) with good correlation. INH concentration in capillary DBS was slightly but not significantly higher than that in venous DBS.The findings of our study show that the analytical performance of this novel method for capillary and venous DBSs was clinically acceptable for the TDM of INH.