Quantifying human calcium absorption using pharmacokinetic methods

Calcium absorption was measured simultaneously by tracer and pharmacokinetic methods in 12 men. The purpose of the study was to calibrate the area under the curve (AUC) for absorptive calcemia to permit comparison or pooling of pharmacokinetic data with tracer-derived estimates. Each subject was studied twice during intake of 500 mg calcium loads (as the carbonate salt), once without excipients, and once with a binder that impeded dissolution of the salt, reducing its absorbability and thereby providing a broad range of absorption values over which to calibrate the method. Various time periods were evaluated, with the best prediction being given by the AUC for the increment in serum calcium calculated over 9 h (AUC₉). For net absorbed calcium (mmol) the relationship was given by 4.358 × AUC₉ ± 0.820. The empirical regression coefficient was significant and the error of the estimate (0.820 mmol) acceptably small.