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Publication:

Author Interview: Jerzy Chudek & Andrzej Wiecek
Daily Magnesium Intake and Hypermagnesemia in Hemodialysis Patients With Chronic Kidney Disease.
Wyskida K, Witkowicz J, Chudek J, Wi?cek A.
J Ren Nutr. 2011 May 25.
Department of Nephrology, Endocrinology and Metabolic Diseases, Medical University of Silesia, Katowice, Poland.

We have demonstrated that magnesium consumption is the most important determinant of serum magnesium concentration in hemodialysis patients with chronic kidney diseases. In univariate analysis, there was a strong positive correlation between magnesium intake and serum concentration in the whole group (r=0.870, p< 0.001). Moreover, we demonstrated that hypermagnesemia was observed in patients ingesting more than 281 mg of magnesium daily. Thus, the described in other studies decreased magnesium absorption in chronic kidney disease is insufficient to prevent the risk of hypermagnesemia.
In the majority of patients, hypermagnesemia was very modest and clinically insignificant. It should be also stressed that in our series of patients, there were no values above 2.0 mmol/L. It has to be emphasized that such hypermagnesemia is usually asymptomatic.

Somehow yes. We expected that residual kidney function and hemodialysis efficacy might be important for magnesium homeostasis. However no correlation between Kt/V or residual diuresis and serum magnesium concentration was found. The lack of correlation between residual diuresis and serum magnesium concentration suggests that magnesium excretion by cirrhotic kidneys is not important for magnesium elimination. The effectiveness of magnesium elimination during HD session is limited due to its slow diffusion from intracellular space, similar to phosphates. Thus, the only way to increase magnesium removal in HD patients is by lowering magnesium concentration in the dialysate fluid.

The use of magnesium-containing phosphate binders in HD patients with poor dietary compliance should be restricted until the reduction of magnesium concentration in dialysate fluid. The recommended dietary intake of magnesium for patients on HD therapy is 200 to 300 mg/day. It seems important to take into consideration that the upper recommended limit of daily magnesium intake should be diminished for HD patients treated with magnesium-containing binders.

Additional ingestion of magnesium-containing phosphate binders should be taken into consideration after measuring magnesium serum concentration in the majority of HD patients. This offers an alternative option in the therapy of hyperphosphatemia in HD patients already receiving calcium binders. Such a therapy is cost effective as has been recently demonstrated by CALMAG study. The use of magnesium containing phosphate binder in CALMAG study was followed by 0.26 mmol/L increase of serum magnesium concentration in mean. The administration of 7 tablets containing 60 mg of elementary magnesium per tablet was shown to be safe, however it should be stressed that patients with even moderate hypermagnesemia (>1.5 mmol/L) were excluded from the study to dampen the risk of significant hypermagnesemia occurrence.

OBJECTIVE:
The aim of this study was to evaluate daily magnesium intake and the relation to its serum concentration in hemodialysis (HD) patients with chronic kidney disease (CKD).
DESIGN:
This is a prospective, open-label, cross-sectional clinical study analyzing daily magnesium intake based on nutritional questionnaire.
PARTICIPANTS:
A total of 101 HD patients with CKD were screened for hypermagnesemia. All patients with serum magnesium >1.5 mmol/L were asked to fill in the standard 3-day nutritional questionnaire. The control group consisted of twice as many randomly selected HD patients with serum magnesium concentration <1.5 mmol/L and 20 subjects with normal kidney function on usual diet.
RESULTS:
Mean (±standard deviation) serum magnesium concentration in HD patients was 1.32 ± 0.18 mmol/L. Hypermagnesemia >1.5 mmol/L was found in 17 (16.8%) patients. There was no one case of severe hypermagnesemia (>2.0 mmol/L). The daily intake of magnesium was higher by 31.7% in the group with serum magnesium >1.5 mmol/L. Hypermagnesemia was observed in patients ingesting >281 mg of magnesium daily. In univariate analysis, there was a strong positive correlation between magnesium intake and serum concentration in the whole group (r = 0.870, P < .001). No correlation between Kt/V or residual diuresis and serum magnesium concentration was found.
CONCLUSIONS:
Magnesium consumption is the most important determinant of serum magnesium concentration in HD patients with CKD. Magnesium-containing phosphate binders can be considered in the therapy of hyperphosphatemia in HD patients without hypermagnesemia.