Long-Term Bioavailability Of Single Doses Of Intramuscular Vitamin D-2

Objective: We sought to determine the long-term bioavailability of single doses of intramuscular (IM) vitamin D-2 (D-2) in healthy adults.Methods: Forty healthy volunteers with hypovitaminosis D received a single dose of 200,000, 400,000, or 600,000 IU intramuscular D-2 or no treatment. Levels of 25-hydroxyvitamin D-2 (25[OH]D-2) and 25-hydroxyvitamin D-3 (25[OH]D-3) in serum were measured by liquid chromatography-tandem mass spectrometry. Vitamin D binding protein (DBP) and intact parathyroid hormone (iPTH), bone turnover markers (BTMs), and serum and urinary calcium were also measured.Results: After a single dose of D-2 injection, the level of 25(OH)D-2 increased slowly and reached a plateau at 8 weeks. The plateau remained stable for 12 weeks. The mean increase in 25(OH)D-2 was 6.8, 9.6, or 15.6 ng/mL after injection of 200,000 IU, 400,000 IU, or 600,000 IU D-2 . Although endogenous 25(OH)D levels were reduced by IM D-2, the total 25(OH)D levels increased by 5.0, 7.0, or 10.3 ng/mL in average after injection of 200,000 IU, 400,000 IU, or 600,000 IU D-2. The iPTH levels were also decreased by IM D-2. However, levels of serum calcium, BTMs, and DBP and urinary calcium were not altered by IM D-2.Conclusion: A single dose of 200,000 IU, 400,000 IU or 600,000 IU IM D-2 raises total 25-hydroxyvitamin D levels by 5.0, 7.0, or 10.3 ng/mL on average for at least 12 weeks and reduces iPTH and endogenous 25(OH)D-3 levels without affecting levels of serum calcium, BTMs, DBP, and urinary calcium.