Background/Objectives: Given the crucial health benefits of vitamin D, addressing severe deficiencies is a pressing medical concern. This study aimed to evaluate the effectiveness and safety of two new weekly doses of calcifediol (100 µg and 125 µg) for long-term management in patients with severe vitamin D deficiency, defined as plasma 25(OH)D levels ≤10 ng/mL. Methods: This study was a randomized, two-cohort, controlled, double-blind, multicentre phase II-III trial. Subjects were randomized 2:2:1 to weekly calcifediol 100 µg, 125 µg or a placebo. The primary endpoint was the proportion of patients achieving plasma 25(OH)D levels of ≥20 ng/mL and/or ≥30 ng/mL by week 16. Results: A total of 276 patients (mean age: 55.2 years, SD 15.42) were randomized. By week 16, 92.3% and 91.8% of patients in the calcifediol 100 µg and 125 µg groups, respectively, reached ≥20 ng/mL, compared to 7.3% in the placebo group. Levels of ≥30 ng/mL were achieved by 49% (100 µg) and 76.4% (125 µg) of participants, with none in the placebo group. Calcifediol demonstrated superior efficacy at all response levels and time points (p < 0.0001). Plasma 25(OH)D concentrations increased by week 24 and remained stable. The incidence of adverse events was comparable across groups. Conclusions: A weekly calcifediol dose of 100 µg demonstrates the best profile of efficacy and tolerability, providing a reliable solution for achieving and maintaining adequate vitamin D levels in patients with severe deficiency.

• Keywords
• calcifediol, efficacy, safety, vitamin D deficiency, weekly treatment,
• MeSH
• Adult MeSH
• Double-Blind Method MeSH
• Calcifediol * administration & dosage   adverse effects   MeSH
• Middle Aged MeSH
• Humans MeSH
• Vitamin D Deficiency * blood   diagnosis   drug therapy   MeSH
• Drug Administration Schedule MeSH
• Aged MeSH
• Vitamin D blood   analogs & derivatives   MeSH
• Treatment Outcome MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Male MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Clinical Trial, Phase II MeSH
• Clinical Trial, Phase III MeSH
• Multicenter Study MeSH
• Randomized Controlled Trial MeSH
• Names of Substances
• Calcifediol * MeSH
• Vitamin D MeSH