Analysis of 47Ca Kinetics in Normal Subjects by Means of a Compartmental Model with a Non-Exchangeable Plasma Calcium Fraction

Abstract

1. 47Ca kinetic studies were performed in eight normal young adult males. Plasma, urinary and faecal stable and radioactive calcium and whole-body radioactivity were measured for up to 40 days after intravenous administration of the tracer. 2. The plasma radioactivity data could be fitted to the sum of four exponentials corresponding to a four-compartment model, but this model did not account for the consistently greater 47Ca specific radioactivities in plasma relative to those in urine at the same time in five of the subjects. 3. A non-exchangeable fraction of plasma calcium estimated as 5% of the mass in the plasma compartment was postulated to account for this finding. 4. An estimate of the insensible losses of calcium was obtained from the whole-body radioactivity counting data.

Population Pharmacokinetics and Pharmacodynamics of the Calcimimetic Etelcalcetide in Chronic Kidney Disease and Secondary Hyperparathyroidism Receiving Hemodialysis

“…A linear threecompartment model with an additional on-HD clearance adequately described the PK of etelcalcetide in patients with SHPT who received etelcalcetide at the end of TIW HD. 11 A number of model-based approaches for describing PTH, 12,13 Ca dynamics, [14][15][16][17][18][19] and the PTH-Ca axis [20][21][22][23][24][25][26] have been proposed. The models vary in degree of complexity and address different mechanisms of action.…”

“…A number of model‐based approaches for describing PTH, Ca dynamics, and the PTH‐Ca axis have been proposed. The models vary in degree of complexity and address different mechanisms of action.…”

A compartmental model of magnesium metabolism in healthy men based on two stable isotope tracers

“…This mathematical description of mineral distribution provides valuable insight into the metabolism of many nutrients in humans (41). Compartmental models have been developed for several essential minerals on the basis of stable isotope studies in humans, including calcium (37,42,43), zinc (13, 21, 31, 38 and 39), copper (6,30), and molybdenum (16,33,34). In addition, parameters deduced from the model can be used as markers of trace element nutritional status.…”

Measuring What Isn’t There

“…This meant that tracer uptake by bone could be used as a direct measure of new bone mineralization. Although various complicated kinetic models were developed (2,3 ), the mathematics were actually quite straightforward. The tracer content of a sample of bone calcium obtained days or weeks after an injection of a calcium isotope into an animal, divided by the average tracer concentration in ECF calcium, directly yields the mass of calcium deposited by bone formation during the interval between tracer injection and the time of the bone sampling.…”