Abstract
It is well known that the serum Magnesium (Mg) level influences the parathyroid hormone (PTH) level: a low Mg level increases and a high Mg level decreases PTH. However, this relationship between Mg and PTH is controversial in uremic patients receiving hemodialysis. We studied the influence of hypermagnesemia on serum PTH levels in patients who were treated by hemodialysis.
We administered phosphate binders to 55 patients [28 males and 27 females, mean age 41.8±9.6 (SD)] for 48 months. The phosphate binders contained Mg (OH)2 and AI2O3. The daily dose of Mg was 300-500mg/day. We measured serum Ca, Mg and P once per month for 48 months. Serum c-terminal PTH (C-PTH) was measured every 6 months by radioimmunoassy.
The administration of phosphate binders increased serum Mg levels from 2.55±0.04mEq/l (mean±SEM) to 2.98±0.05mEq/l after 6 months; and these elevated Mg levels were maintained up to the end of the study. In 41 patients (74%), serum PTH levels significantly decreased within 12 months of Mg repletion from 2.50±0.34ng/ml to 1.47±1.20ng/ml (p<0.01: Responders). But this effect was transient. After 18 months, its levels increased again despite the elevated Mg levels. In the other patients, serum PTH levels did not decrease in spite of Mg repletion (Non-responders).
In both groups, however serum phosphorus levels decreased after the administration of phosphate binders, while serum Ca levels did not change significantly.
We have demonstrated that hypermagnesemia induced by phosphate binders decreases serum PTH levels; but the effect does not last more than 18 months.
