Quantification of isoniazid, pyrazinamide and ethambutol in serum using liquid chromatography-tandem mass spectrometry

Clinical studies on tuberculosis have shown a correlation between low drug exposure and treatment failure and acquired drug resistance. Objective was to develop a LC-MS/MS method for the quantification of isoniazid, pyrazinamide and ethambutol. Stable isotope-labelled isoniazid-D4 and ethambutol-D4 were used as internal standards. Protein binding of isoniazid, pyrazinamide and ethambutol was investigated and proved low. Therefore, sample preparation using ultrafiltration could be applied, resulting in linear calibration curves in the range of 0.2-8 mg/L for isoniazid and ethambutol and 2-80 mg/L for pyrazinamide. The method was validated according to the guidelines of the FDA. A fast, simple and reliable LC-MS/MS method has been developed for the simultaneous determination of isoniazid, pyrazinamide and ethambutol in human serum for therapeutic drug monitoring and pharmacokinetic studies.