Fingerprick Microsampling Methods Can Replace Venepuncture for Simultaneous Therapeutic Drug Monitoring of Tacrolimus, Mycophenolic Acid, and Prednisolone Concentrations in Adult Kidney Transplant Patients

Background: Kidney transplant patients undergo repeated and frequent venepunctures during allograft management. Microsampling methods that use a fingerprick draw of capillary blood, such as dried blood spots (DBS) and volumetric absorptive microsamplers (VAMS), have the potential to reduce the burden and volume of blood loss with venepuncture. Methods: This study aimed to examine microsampling approaches for the simultaneous measurement of tacrolimus, mycophenolic acid, mycophenolic acid glucuronide (MPAG), and prednisolone drug concentrations compared with standard venepuncture in adult kidney transplant patients. DBS and VAMS were simultaneously collected with venepuncture samples from 40 adult kidney transplant patients immediately before and 2 hours after immunosuppressant dosing. Method comparison was performed using Passing-Bablok regression, and bias was assessed using Bland-Altman analysis. Drug concentrations measured through microsampling and venepuncture were also compared by estimating the median prediction error (MPE) and median absolute percentage prediction error (MAPE). Results: Passing-Bablok regression showed a systematic difference between tacrolimus DBS and venepuncture [slope of 1.06 (1.01-1.13)] and between tacrolimus VAMS and venepuncture [slope of 1.08 (1.03-1.13)]. Tacrolimus values were adjusted for this difference, and the corrected values showed no systematic differences. Moreover, no systematic differences were observed when comparing DBS or VAMS with venepuncture for mycophenolic acid and prednisolone. Tacrolimus (corrected), mycophenolic acid, and prednisolone microsampling values met the MPE and MAPE predefined acceptability limits of