Association Between Hematocrit- and Lymphocyte-Adjusted Tacrolimus Concentration and Clinical Outcomes in Dermatomyositis-Associated Interstitial Lung Disease: A Short Communication

BACKGROUND: Tacrolimus (TAC) is extensively distributed in blood cells, and the total blood concentration (Ctot) may overestimate pharmacologically active exposure, particularly in inflammatory conditions. We explored the association between TAC concentration adjusted for hematocrit (%) and lymphocyte count (Cadj) and clinical outcomes in patients with dermatomyositis-associated interstitial lung disease. METHODS: Patients in whom TAC therapy was initiated were stratified into 3 groups according to the Cadj/Ctot ratio. The association between exacerbation of ILD and acute kidney injury [AKI] was evaluated. RESULTS: A total of 23 patients were included, and 7, 7, and 9 were stratified into the low, intermediate, and high Cadj/Ctot ratio groups, respectively. There was exacerbation of ILD in 57% and 12.5% of patients in the low and intermediate/high Cadj/Ctot ratio groups, respectively (odds ratio, 8.2; 95% confidence interval, 0.78-134; P = 0.045). There was AKI in 44% and 28.5% of patients in the high and low/intermediate Cadj/Ctot ratio groups, respectively; however, the difference was not statistically significant. CONCLUSIONS: Cadj-based therapeutic drug monitoring may more accurately reflect clinical outcomes than conventional Ctot-based monitoring.