Vitamin D deficiency is frequent in the general population and both subjects and health professionals could benefit from a broader range of vitamin D3 formulations. We conducted a single-dose, open-label, parallel-group, randomized bioequivalence study to compare a single dose of a newly developed vitamin D3 100,000 IU in a soft capsule (Group 1) with the reference drug vitamin D3 100,000 IU oral solution in ampoule (Group 2) in healthy volunteers over a four-month period. The primary endpoint was the area under the curve (AUC) of serum 25-hydroxyvitamin-D (25(OH)D) concentrations on Day 112. This study was conducted in France from February to June 2014 in 53 young adults with a mean age of 26.9 years. At baseline, low mean serum 25(OH)D levels were observed in both groups (10.6 ng/mL in Group 1 and 9.0 ng/mL in Group 2). On Day 112, the AUC of serum 25(OH)D concentration was 2499.4 ± 463.8 nmol/mL (7.8 ± 0.2 for LogAUC) for Group 1 and 2152.3 ± 479.8 nmol/mL (7.6 ± 0.2 for LogAUC) for Group 2. Bioequivalence of the two treatments was not demonstrated. Superiority of vitamin D3 100,000 IU soft capsule was observed with p = 0.029 for AUC and p = 0.03 for LogAUC using a non-parametric Wilcoxon test. The profile of the serum 25(OH)D concentration showed a significant difference in favor of Group 1 on Days 1, 3, 7, 14 and 90. Mean serum 25(OH)D concentrations in Group 1 were between 20 and 30 ng/mL during the four-month period and under 20 ng/mL throughout the study in Group 2, except on Day 112. Mean Cmax for Group 1 was significantly higher (p = 0.002). Fourteen days were needed to reach Tmax by more than half the subjects in Group 1 compared to 45 days in Group 2. Both treatments were well tolerated, with no severe or related adverse events reported. In conclusion, the pharmacokinetic profile of the new formulation of vitamin D3 100,000 IU soft capsule is superior to that of the oral solution in ampoule. The new formulation increased serum 25(OH)D levels to above 20 ng/mL and maintained levels from 20 ng/mL to 30 ng/mL for four months in late winter and spring.
Keywords: 100,000 IU soft capsule; 25(OH)D; oral supplementation; pharmacokinetics; single dose; vitamin D.