Purpose
Replicating the physiological cortisol secretion is key in the treatment of glucocorticoid insufficient individuals and optimization may enhance quality of life. The study investigates fatigue measured by ecological momentary assessments in patients treated with conventional hydrocortisone compared with once-daily dual-release hydrocortisone (Plenadren).

Methods
A 21-week open-label switch pilot trial included 30 patients with adrenal insufficiency due to hypopituitarism. Fatigue was assessed four times daily for 20 days using a momentary item version of the Multidimensional Fatigue Inventory on patients’ usual hydrocortisone regimen. Participants switched treatment to an identical daily dose of Plenadren for 16 weeks where fatigue assessments were repeated. Change in fatigue and diurnal variation of fatigue was analyzed using mixed models for repeated measurements.

Results
In four out of five fatigue subscales fatigue was significantly reduced 0.7–1.1 points (scales ranging from 4 to 20), when treated with Plenadren compared with conventional hydrocortisone, corresponding to small effect sizes below the scale-specific minimal important changes. However, 33% of the participants completing the study (9/27) experienced reductions in fatigue above the minimal important change. On Plenadren, we found larger between-person variances and smaller within-person variances. Finally, we identified diurnal fatigue curves for both treatments.

Conclusions
The Plenadren-related reduction in fatigue was significant but not necessarily of clinical importance when looking at a group level. However, there was a large interindividual variation in treatment effect, why patients with a large benefit in quality of life should be identified. Future RCTs should be powered to detect the effect magnitudes identified here.