Magnesium status in chronically haemodialyzed patients: the role of dialysate magnesium concentration

Serum magnesium concentration (sMg) increases in advanced renal failure, and in patients on regular dialysis treatment Mg status mainly depends upon the dialysate Mg concentration (dMg). In fact in uraemia, whereas the intracellular (muscle and blood cell) Mg content seems similar to that of normals and not to be influenced by dMg, the extracellular fluid Mg level as well as Mg content in some organs (skin, bone, etc) parallel the dMg. In the present paper, Mg status and its clinical implications in patients on regular dialysis treatment were therefore reviewed in an attempt to define an optimal dMg. Up to now, dialysis patients have been kept hypermagnesaemic on the assumption that a high sMg suppresses parathyroid hormone secretion (PTH), although this hypothesis has not been confirmed in later papers. On the other hand, more recent clinical studies suggest the possibility of noxious effects of Mg overload on various organs. Therefore, future trends should be towards reducing dMg to such values as will allow sMg to fluctuate across the normal range both in the interdialytic and intradialytic period. The more widespread use of Mg-containing phosphate binders implies the need of a further reduction of dMg which, however, carries the risk of symptomatic postdialytic hypomagnesaemia. Thus, since Mg is retained in uraemia and should be removed by dialysis, it is difficult to associate the use of Mg-containing drugs with an optimal dMg while avoiding severe hypermagnesaemia and hypomagnesaemia.