title: Calcium bioavailability of calcium L-threonate in healthy Chinese subjects measured with stable isotopes (⁴⁴Ca and ⁴²Ca).
abstract: OBJECTIVE
  Calcium L-threonate is a novel drug that was developed for the treatment of osteoporosis and as a calcium supplement. However, calcium bioavailability of this drug is unknown due to lack of effective evaluation methods. In this study, we sought to measure the bioavailability of calcium L-threonate with a double-label stable isotope method.
  
  
  METHODS
  Fourteen healthy Chinese subjects were enrolled in the clinical study and were given 300 mg calcium L-threonate tablets containing 40 mg (44)Ca after an intravenous injection of 4 mg (42)Ca solution (as calcium chloride). Fractional urine samples were collected at the following time intervals: 0-3, 3-6, 6-9, 9-13, 13-24, 24-36 and 36-48 h. The abundance ratios of (44)Ca/(40)Ca and (42)Ca/(40)Ca in the urine were determined with thermal-ionization mass spectrometry (TI-MS). The calcium bioavailability was estimated by calculating the true fractional calcium absorption (TFCA) using the abundance ratios of (44)Ca/(40)Ca and (42)Ca/(40)Ca.
  
  
  RESULTS
  The bioavailability of calcium L-threonate in 14 healthy Chinese subjects was 26.49 ± 9.39 %. There was good agreement between TFCA from the 24 to 36 h and the 36 to 48 h urine pool, indicating that calcium balance was achieved at 24 h after dosing. The TFCA of the subjects did not statistically correlate with total urinary calcium excretion (0-48 h). There were no serious adverse events in this study.
  
  
  CONCLUSIONS
  The bioavailability of calcium L-threonate in humans was successfully determined by estimating TFCA with the double-label stable isotope method, thus providing a useful approach for the evaluation of bioavailability of calcium formulations.
authors.affiliation: Clinical Pharmacology Research Center, Peking Union Medical College Hospital, No.1 Shuai FuYuan, Dong Cheng District, Beijing 100730, People's Republic of China. wanghongyunpharm@yahoo.com
authors.forename: Hongyun
authors.initials: H
authors.lastname: Wang
authors.forename: Pei
authors.initials: P
authors.lastname: Hu
authors.forename: Ji
authors.initials: J
authors.lastname: Jiang
mesh_terms: D000328:Adult; D044466:Asian People; D001682:Biological Availability; D002087:Butyrates / Q000009:adverse effects / Q000493:pharmacokinetics*; D002118:Calcium / Q000652:urine*; D002127:Calcium Isotopes / Q000652:urine*; D005260:Female; D006801:Humans; D008297:Male
chemical_list: D002087:Butyrates; D002127:Calcium Isotopes; C011369:threonic acid; D002118:Calcium