Anders Åsberg

Background Reliable methods to detect and reduce medication nonadherence in solid organ‐transplanted (SOT) adolescents are warranted. We aimed to evaluate the feasibility of combining a medication‐manager application (TusenTac®‐app) with home‐sampling of tacrolimus (Tac) in young SOT recipients. Methods Kidney and combined SOT recipients between 14 and 25 years were included. During an 8‐week intervention period, the participants were instructed to use the transplant‐specific, age‐adapted TusenTac®‐app daily and to perform weekly at‐home Tac trough finger‐prick microsampling. Microsample Tac concentrations were controlled against timed venous samples twice. Medication implementation and persistence adherence were measured with BAASIS© questionnaires, TusenTac®‐registrations, Tac trough concentration coefficient of variation (CV%) and self‐reporting by interview. For comparison, venous Tac trough CV% were obtained from the year before and after the short‐term intervention. Results Twenty‐two recipients were included, two withdrawals, leaving 20; median age 17.9 (14.5–24.8) years, 12 females (60%). The participants registered their dosage intake 88% (1502/1703) of the expected times, and 90% (106/118) of the microsamples were obtained correctly. At inclusion, 11 recipients (55%) were nonadherent assessed with BAASIS© questionnaire, four of these (36%) turned adherent during the intervention period. At the end, 70% reported improved timing‐adherence at the interview. There was no significant change in TacCV% from the year before to the year after the short‐term intervention. Home‐sampling was reliable and measured Tac concentrations accurately. Conclusions Home‐monitoring, combining Tac finger‐prick microsampling and a medication‐manager app, is feasible in adolescent SOT recipients with 70% perceived improvement in medication timing‐adherence. There were no significant long‐term changes in TacCV% confirming the need for continuous use and individualized interventions.

In combination with Bayesian estimates based on a population pharmacokinetic model, limited sampling strategies (LSS) may reduce the number of samples required for individual pharmacokinetic parameter estimations. Such strategies reduce the burden when assessing the area under the concentration versus time curves (AUC) in therapeutic drug monitoring. However, it is not uncommon for the actual sample time to deviate from the optimal one. In this work, we evaluate the robustness of parameter estimations to such deviations in an LSS. A previously developed 4-point LSS for estimation of serum iohexol clearance (i.e., dose/AUC) was used to exemplify the effect of sample time deviations. Two parallel strategies were used: (a) shifting the exact sampling time by an empirical amount of time for each of the four individual sample points, and (b) introducing a random error across all sample points. The investigated iohexol LSS appeared robust to deviations from optimal sample times, both across individual and multiple sample points. The proportion of individuals with a relative error greater than 15% (P15) was 5.3% in the reference run with optimally timed sampling, which increased to a maximum of 8.3% following the introduction of random error in sample time across all four time points. We propose to apply the present method for the validation of LSS developed for clinical use.