The purpose of this study was to determine the intrapatient (within the same patient) variability of tacrolimus in adherent patients. Daily tacrolimus trough levels were obtained at home using dried blood spot technology in kidney and liver transplant recipients. Patients were randomized to receive 3 formulations of tacrolimus, each for two 1-week periods. Adherence was monitored by patient diary, pill counts, and use of the Medication Event Monitoring System (MEMS). Variability was quantified as the coefficient of variation (CV). Comparison of CV between groups was by independent t test or one-way ANOVA as appropriate. The population was found to be adherent with a rate of 99.9% with a mean interval between the evening and morning dose of tacrolimus of 11.86 hours. The median CV for the entire population was 15.2% (range 4.8%-110%). There were no differences in CV by allograft type or tacrolimus formulation. The multivariate analysis did not identify any demographic characteristics associated with a CV > 30%. In a highly adherent population, tacrolimus did not display high intrapatient variability. Given the association between IPV and poor allograft outcomes, future studies are needed to quantitate the influence of adherence and establish target IPV goals. K E Y W O R D S clinical research/practice, compliance/adherence, immunosuppressant -calcineurin inhibitor, immunosuppression/immune modulation, kidney transplantation/nephrology, liver transplantation/hepatology, tacrolimus | 1411 LEINO Et aL.

Cannabidiol (CBD), a major purified nonpsychoactive component of cannabis with anticonvulsant properties, was approved by the U.S. Food and Drug Administration (FDA) in June 2018 as an adjuvant treatment for refractory epilepsy (Epidiolex; GW Pharmaceuticals). CBD is metabolized by cytochrome P450 (CYP)3A4 and CYP2C19 with a growing body of evidence suggesting it is also a potent inhibitor of these pathways. We report for the first time a significant drug‐drug interaction between the purified CBD product and tacrolimus. A participant in a CBD clinical trial for epilepsy who was also receiving tacrolimus showed an approximately 3‐fold increase in dose‐normalized tacrolimus concentrations while receiving 2000‐2900 mg/day of CBD. Our report delineates an important concern for the transplant community with the increasing legalization of cannabis and advent of an FDA‐approved CBD product. Larger studies are needed to better understand the impact of this drug‐drug interaction in solid organ transplant recipients.

Background Tacrolimus therapy in solid organ transplant (SOT) recipients is challenging due to its narrow therapeutic window and pharmacokinetic variability both between patients and within a single patient. Intrapatient variability (IPV) of tacrolimus trough concentrations has become a novel marker of interest for predicting transplant outcomes. The purpose of this review is to evaluate the association of tacrolimus IPV with graft and patient outcomes and identify interventions to improve IPV in SOT recipients. Methods A systematic review of the literature was performed using PubMed and Embase from database inception to September 20, 2020. Studies were eligible only if they evaluated an association between tacrolimus IPV and transplant outcomes. Both pediatric and adult studies were included. Measures of variability were limited to standard deviation, coefficient of variation, and time in therapeutic range. Results Forty‐four studies met the inclusion criteria. Studies were published between 2008 and 2020 and were observational in nature. Majority of data were published in adult kidney transplant recipients and identified an association with rejection, de novo donor specific antibody (dnDSA) formation, graft loss, and patient survival. Evaluation of IPV‐directed interventions was limited to small preliminary studies. Conclusions High tacrolimus IPV has been associated with poor outcomes including acute rejection, dnDSA formation, graft loss, and patient mortality in SOT recipients. Future research should prospectively explore IPV‐directed interventions to improve transplant outcomes.

Starting in 2015, the American Society of Transplantation Psychosocial Community of Practice, with representatives of the Transplant Pharmacy Community of Practice, convened a taskforce to develop a white paper that focused on clinically practical, evidenced-based interventions that transplant centers could implement to increase adherence to medication and behavioral recommendations in adult solid organ transplant recipients. The group focused on what centers could do in their daily routines to implement best practices to increase adherence in adult transplant recipients. We developed a list of strategies using available resources, clinically feasible methods of screening and tracking adherence, and activities that ultimately empower patients to improve their own self-management. We limited the target population to adults because they predominate the research, and because adherence issues differ in pediatric patients, given the necessary involvement of parents/guardians. We also examined broader multilevel areas for intervention including provider and transplant program practices. Ultimately, the task force aims to foster greater recognition, discussion, and solutions required for implementing practical interventions targeted at improving adherence.

Dose modification of immunosuppressants post-LSG may not be necessary aside from standard therapeutic drug monitoring.