Analytical and clinical validation of a volumetric absorptive microsampling (VAMS) - Ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the analysis of Clofazimine in whole blood.

Monitoring clofazimine blood concentrations is crucial for preventing treatment failure in patients with Multidrug-resistant Tuberculosis (MDR-TB). Volumetric Absorptive Microsampling (VAMS) offers a practical alternative to Conventional Venous Sampling (CVS), enabling remote sampling. Samples collected via VAMS can be conveniently transported to laboratories via courier, enhancing accessibility and patient compliance. In this study, we developed and validated an analytical method for quantifying clofazimine in whole blood collected using VAMS. The study compared the performance and cost-effectiveness of VAMS with CVS. A total of 55 matched finger-prick VAMS and CVS samples were obtained from 39 MDR-TB patients and analyzed using validated UPLC-MS/MS assays. Clofazimine concentrations collected via VAMS and CVS were compared using Passing-Bablok regression, while bias and overall agreement were evaluated through Bland-Altman analysis. Passing-Bablok regression revealed no significant constant difference between VAMS and CVS (95% CI slope: 0.7627-0.9573; 95% CI intercept: -0.02141-0.06482), but systematic difference of 13% lower clofazimine concentrations was observed in VAMS compared to plasma. Bland-Altman analysis demonstrated moderate agreement, with mean plasma/VAMS ratio of 0.9457 (95% CI: 0.88358-1.00775) and 95% Limits of Agreement (LoA) ranging from 0.4956 (95% CI: 0.38881-0.60230) to 1.3858 (95% CI: 1.28903-1.50252). Although statistically significant bias was identified, applying correction factors could improve interchangeability between the two techniques. Furthermore, VAMS was more cost-effective than CVS, with approximate cost difference of 4.45 USD per sample. These findings suggest that VAMS sampling has the potential to replace CVS for routine clinical monitoring of clofazimine, offering a more accessible and economical approach.