Quantification of isoniazid and acetylisoniazid in rat plasma and alveolar macrophages by liquid chromatography–tandem mass spectrometry with on-line extraction

To evaluate if pulmonary delivery of microparticles loaded with a prodrug of isoniazid (INH), isoniazid methanesulfonate (INHMS), can target alveolar macrophages (AM) and reduce metabolism of INH, an HPLC–MS/MS assay with automated online extraction for quantification of INH and its metabolite acetylisoniazid (AcINH) in plasma and AMs was developed and validated. Reproducibility in rat plasma and homogenate of a rat AM cell line, NR8383, for INH and AcINH showed excellent precision and accuracy with calibration curves exhibiting linearity within a range of 1–250 ng/ml of INH and 0.05–50 ng/ml of AcINH (r2 > 0.99). The validated methods were successfully applied to pharmacokinetic study of INHMS-loaded microparticles in rats, demonstrating efficient targeting of AMs and reduction of INH metabolism.