Improvements in Serum 25(OH)D Following Stoss Dosing in People With Cystic Fibrosis and Variable Adherence to Maintenance Regimens: A Retrospective Chart Review.

Background and Aims: People with cystic fibrosis (pwCF) often have vitamin D deficiency and require vitamin D supplementation. The primary objective of this study was to evaluate the impact of ultrahigh dose cholecalciferol ("stoss dosing") in pwCF with variable adherence to maintenance cholecalciferol. Methods: Retrospective cohort study of pwCF who received initial stoss dose per protocol between January 2017 and November 2021 at University of Iowa Health Care adult and pediatric CF centers. Serum 25(OH)D concentrations were extracted from the EMR. The increase in serum 25(OH)D concentration associated with receiving stoss doses was evaluated using a longitudinal linear mixed effects regression model. Results: Fifty-eight patients were included in the final analysis. The mean baseline 25(OH)D concentration before stoss therapy was 20.1 ng/mL (standard deviation [SD] = 5.9). The mean serum 25(OH)D concentration following stoss therapy increased to 27.9 ng/mL (SD = 7.5) and was measured on average 116 days after stoss administration. For patients with self-reported non-adherence to vitamin regimens, 16 out of 20 (80%) achieved a serum 25(OH)D concentration of at least 30 ng/mL after stoss therapy. Conclusions: Our findings suggest that stoss dosing was associated with increased serum 25(OH)D concentrations. This benefit also existed for individuals with self-reported non-adherence to maintenance cholecalciferol regimens with most patients reaching concentration goals.