A New Phototherapy Regimen Coupled with Oral Vitamin D Supplementation, for the Long-Term Control of Atopic Dermatitis: A French Multicenter, Randomized, Crossover, Pragmatic Trial

The global burden of atopic dermatitis (AD) will continue to rise in the coming two decades, underscoring the need for affordable and globally accessible therapies given restricted access to high-cost medications in many regions. The study aimed to evaluate the efficacy of a novel phototherapy-based regimen as an add-on therapy, together with vitamin D supplementation, on long-term disease control in AD. The PRADA trial combined two independent randomizations within the same population: an open-label, crossover comparison of narrowband ultraviolet B (NB-UVB) phototherapy versus observation, and a double-blind, parallel-group comparison of vitamin D versus placebo, both superimposed on standard topical anti-inflammatory treatments (TAT). It was conducted between 2015 and 2023 across 16 French hospital centers. The trial included patients aged ≥ 15 years with moderate-to-severe (IGA > 2) AD and with fewer than 100 lifetime phototherapy sessions. The primary outcome was a hierarchical composite endpoint based on: (1) repeated measures of Patient-Oriented SCORing Atopic Dermatitis (PO-SCORAD) severity score over 1 year; and (2) the cumulative use of TAT from October to March. A total of 53 participants were allocated to the vitamin D (26 received NB-UVB during the first period), and 57 to the placebo (27 received NB-UVB during the first period). A total of 93 participants were available for the main analysis for the primary endpoint. Vitamin D was significantly associated with lower PO-SCORAD scores compared with placebo (mean [95% CI] difference −5.6 [−12.1 to −1.78]), however, this effect size remained below the prespecified minimum clinically important difference (nine points). NB-UVB showed no significant effect on PO-SCORAD scores (mean difference: 1.25 [−3.90 to 1.40]). Adverse event incidence was 0.33 per 100 patient-months, mainly nonserious photosensitivity reactions ( n = 38). In the PRADA trial (underpowered due to a recruitment short fall), NB-UVB phototherapy showed no clinically meaningful benefit on the long-term control of moderate-to-severe AD. The observed benefit of vitamin D supplementation on PO-SCORAD, although statistically significant, did not reach the threshold for clinical relevance. ClinicalTrials.gov Identifier: NCT02537509.