RESUMO
Introduction: Isoniazid (INH) is one of the most effective and potent first-line anti-tubercular drug. INH is also effectively administered as a preventative monotherapy and has been shown to significantly reduce TB incidence. INH is primarily metabolised to acetyl-isoniazid (AcINH) in the liver. AcINH is mainly excreted in urine presenting as a target for monitoring adherence to INH therapy. Objective: The study aimed to develop and fully validate a bioanalytical method using liquid chromatography-tandem mass spectrometry for the quantification of INH and AcINH in human urine. Methods: The samples were prepared using solid phase extraction, with the internal standards isoniazid-d4 and acetyl-isoniazid-d4 being used. The extracts were chromatographed on an Atlantis T3 analytical column with an isocratic mobile phase. For detection, a AB Sciex™ API 5500 triple quadrupole mass spectrometer was used at unit resolution in the multiple reaction monitoring mode, following positive electrospray ionization. Results: The analytical method demonstrated sufficient sensitivity, as indicated by average signal-to-noise ratios of 7.07 and 6.23 at the lower limit of quantification for INH and AcINH, respectively. Validation was performed over three consecutive batches, demonstrating accuracy, precision, and overall robustness based on peak area ratios within the analytical range of 0.234-30.0 µg/mL for both INH and AcINH. All required validation experiments were assessed and met the acceptance criteria guidelines of the US Food and Drug Administration and European Medicines Agency. The validated method was utilized to measure concentrations of AcINH in urine as a means of assessing adherence to the intake of isoniazid in order to prevent TB infection during a phase III open-label multicenter trial. Conclusion: A bioanalytical method was developed and fully validated for quantifying isoniazid (INH) and acetyl-isoniazid (AcINH) in 100 µL of human urine.