Background Nilotinib (Tasigna) is a tyrosine kinase inhibitor (TKI) used in the treatment of chronic myeloid leukaemia (CML). Non-adherence to TKIs affects treatment efficacy and leads to higher morbidity and, possibly, mortality in patients with CML. Therapeutic drug monitoring (TDM) could be useful to identify unacceptably low concentrations resulting from non-adherence, pharmacokinetics or other reasons, or unacceptably high concentrations, possibly causing side effects. Compared to conventional venous blood sampling, dried blood spot (DBS) sampling is a convenient and simple sampling method with lower costs and better patient comfort.

Purpose To evaluate nilotinib concentrations in DBS versus venous blood samples in patients with CML for TDM and research purposes.

Materials and methods A cross-sectional validation study of nilotinib in DBS samples was conducted in VU University Medical Centre in Amsterdam, The Netherlands. DBS and venous blood samples were collected simultaneously from 40 patients. Nilotinib concentrations were analysed using a validated method with LC-MS/MS. Nilotinib concentrations in DBS were corrected for haematocrit.

Results Forty duplicate DBS and venous blood samples were collected from 20 patients (65% male, mean age 56 ± 14 years). Mean haematocrit of the venous blood samples was 0.41 ± 0.05 L/L. Nilotinib concentrations ranged from 233 to 2579 mcg/L in DBS samples corrected for haematocrit and from 376 to 2633 mcg/L in venous blood samples. Using the general Deming regression, the slope was 0.94 with a standard error of 0.07 (95% CI, 0.79–1.09).

Conclusions This study demonstrated that sampling nilotinib in DBS seems a valid alternative to sampling nilotinib in venous blood in patients with CML. DBS sampling may be applicable for TDM and research purposes.

No conflict of interest.