Elexacaftor/tezacaftor/ivacaftor in liver or kidney transplanted people with cystic fibrosis using tacrolimus, a drug-drug interaction study

•The drug-drug interaction between tacrolimus and elexacaftor/tezacaftor/ivacaftor resulted in an increased exposure of tacrolimus in all subjects.•No adverse events were reported during the study period.•Close monitoring of tacrolimus trough levels is recommended in patients who start ETI treatment. The use of elexacaftor/tezacaftor/ivacaftor (ETI) in people with cystic fibrosis (pwCF) after solid organ transplantation is controversial because of potential drug-drug interactions (DDI) with tacrolimus. We aimed to improve insight into the safety and clinical benefits of co-administration of ETI and tacrolimus in liver or kidney transplanted adult pwCF. In 5 pwCF, tacrolimus concentrations were monitored during 2 weeks before and 4 weeks after starting ETI treatment. Trough levels, area under the curve (AUC) and clinical effect of ETI were investigated. During the study (6 weeks in total) adverse events were monitored. The DDI between tacrolimus and ETI resulted in an increased exposure of tacrolimus in all subjects, the dose adjusted AUC0-24h was 1.79 (median) times higher at the end of the study. Five dose adjustments were performed in 4 subjects in order to attain tacrolimus target range. No adverse events were reported and all subjects showed clinical improvement during ETI treatment. The clinical value of ETI treatment in kidney and liver transplanted pwCF is clear. The use of ETI may increase tacrolimus levels moderately. Therefore, we recommend close monitoring of tacrolimus trough levels in patients who start ETI.