25-Hydroxyvitamin D Pharmacokinetic Study

Patients with a history of intestinal malabsorption (n=10) and healthy volunteers (n=10); (of both sexes and all ethnicities) will be recruited in this randomized double-blind crossover study. All subjects will be prescreened for 25(OH)D levels to include subjects with 25(OH)D\<30 ng/ml. The subjects will be randomized to receive a single oral dose of 900 µg of either vitamin D3 or 25(OH)D3. Blood samples will be taken at baseline and at 2,4,6,8,12 hours and days 1,2,3, 7 and 14. After a washout period of at least 14 days (2 weeks) the subjects will receive in a double blinded manner a single oral dose of 900 µg of either 25(OH)D3 or vitamin D3 (depending on which one they took in the randomization) any time after the washout. Blood samples will be taken at baseline and at 2,4,6,8,12 hours and days 1,2,3,7, 14. Serum levels of calcium, phosphorus, albumin, creatinine, intact parathyroid hormone (iPTH) will be obtained at baseline and at day 14 (or within a reasonable time if unable to come in on the exact day). Vitamin D and 25(OH)D will be determined on all the blood samples collected at the various times.