Effects of a magnesium-free dialysate on magnesium metabolism during continuous ambulatory peritoneal dialysis

Hypomagnesemia in Continuous Ambulatory Peritoneal Dialysis Patients Dialyzed with a Low-Magnesium Peritoneal Dialysis Solution

Objective

Previous studies have shown a decrease in serum magnesium (Mg) concentration when continuous ambulatory peritoneal dialysis (CAPD) patients previously maintained on a 1.0 –1.2 mEq/L Mg peritoneal dialysis solution (PDS) were dialyzed with a 0.5 mEq/L Mg PDS. However, the prevalence of hypomagnesemia in CAPD patients dialyzed with low-Mg PDS is unknown.

Design

A retrospective study to determine the prevalence of hypomagnesemia and the factors associated with its occurrence in CAPD patients dialyzed using a 0.5 mEq/L Mg PDS.

Setting

A CAPD unit in a large Veterans Affairs Hospital.

Patients

All our CAPD patients (33) enrolled over a 52month period.

Results

All patients had serum magnesium levels higher than 1.25 mEq/L prior to use of low-Mg PDS. Hypomagnesemia (serum Mg < 1.25 mEq/L) developed in 21/33 patients (64%) when a 0.5 mEq/L Mg PDS was employed. Hypomagnesemia developed a mean of 8.2 months after beginning treatments. The duration of dialysis and the number of episodes of peritonitis did not differ between patients with and those without hypomagnesemia. Serum albumin levels were significantly lower in patients with hypomagnesemia (2.5±0.12 g/dL vs 3.2±0.12, p < 0.01). Magnesium supplements were given to 13 patients; following this therapy, serum magnesium values became normal.

Conclusions

CAPD patients dialyzed with a 0.5 mEq/L Mg PDS may develop a considerable fall in serum magnesium level and may require magnesium supplements in order to restore normal serum values.

Measurement of Serum Ionized Magnesium in Capd Patients

Objective

To evaluate the magnesium status of continuous ambulatory peritoneal dialysis (CAPD) patients using a new method for assessing the level of the ionized fraction a serume magnesiumy.

Design

Serum ionized magnesium was measured in CAPD patients using the ion-selective electrode for Mg2+.

Setting

The Dialysis Unit of Tampere University Hospital.

Patients

Twenty -six patients on CAPD (age: 21 -81 years, mean 54 ± 16 years; duration of CAPD: 3 -52 months, mean 13 months), and 26 sex and age-matched healthy controls.

Results

Both serum ionized magnesium (0.73 ± 0.11 mmol/L vs 0.56 ± 0.07 mmol/L, p < 0.001) and total magnesium (1.11 ± 0.22 vs 0.81 ± 0.08 mmol/L, p < 0.01) were higher in CAPD patients than in sex and agematched controls. The ionized magnesium fraction of total magnesium was slightly lower in dialysis patients in spite of the fact that 16/26 patients had serum albumin less than 36 g/L. Hypermagnesemia (mean serum ionized magnesium 0.78± 0.10 mmol/L) was observed in the 13 of 26 patients with 0.75 mmol/L Mg2+ dialysate; those with lower magnesium dialysate (Mg2+ 0.50 mmol/L in 10/26 and Mg2+ 0.25 mmol/L in 3/26) had mean serum ionized magnesium at the upper normal margin (0.69 ± 0.10 mmol/L).

Conclusion

In CAPD patients with Mg2+ 0.5 0.75 mmol/L in their dialysis fluid, both serum ionized and total magnesium concentrations were higher but the ionized/total magnesium ratio was lower than in healthy control subjects. Use of ion-selective electrodes to measure ionized magnesium may be a more useful methodology than measuring total magnesium in the evaluation of magnesium status of CAPD patients, because it is not infuenced by hypoalbuminemia or increased complexed fraction of magnesium often present in dialysis patients.

Relationship between Serum Magnesium, Parathyroid Hormone, and Vascular Calcification in Patients on Dialysis: A Literature Review

Secondary hyperparathyroidism is present in most patients with end-stage renal disease and has been linked to uremic bone disease, vascular calcification, and mortality. Current literature suggests an association between hypomagnesemia and cardiovascular disease in the general population. We reviewed all published studies on the relationship between serum magnesium and parathyroid hormone and the relationship between serum Mg and vascular calcification in dialysis patients. Of these, 10 of 12 studies of patients on hemodialysis and 4 of 5 studies of patients on peritoneal dialysis showed a significant inverse relationship between serum Mg and serum intact parathyroid hormone. Hyperparathyroidism develops in peritoneal dialysis patients dialyzed with a solution containing normal calcium (1.25 mmol/L) and low Mg (0.25 mmol/L), even though serum calcium is maintained at a normal level. Four of the hemodialysis studies and one of the peritoneal dialysis studies indicated that there is an inverse relationship between serum Mg and vascular calcification in these patients. Potential benefits have been attributed to magnesium carbonate as a phosphate binder and it may possibly be an effective, less toxic, less expensive phosphate binder. We believe that the role of Mg in secondary hyperparathyroidism and vascular calcification merits further investigation.

Serum magnesium and cardiovascular mortality in peritoneal dialysis patients: a 5-year prospective cohort study

The aim of this study was to explore the association between serum Mg and cardiovascular mortality in the peritoneal dialysis (PD) population. This prospective cohort study included prevalent PD patients from a single centre. The primary outcome of this study was cardiovascular mortality. Serum Mg was assessed at baseline. A total of 402 patients (57 % male; mean age 49·3±14·9 years) were included. After a median of 49·9 months (interquartile range: 25·9-68·3) of follow-up, sixty-two patients (25·4 %) died of CVD. After adjustment for conventional confounders in multivariate Cox regression models, being in the lower quartile for serum Mg level was independently associated with a higher risk of cardiovascular mortality, with hazards ratios of 2·28 (95 % CI 1·04, 5·01), 1·41 (95 % CI 0·63, 3·16) and 1·62 (95 % CI 0·75, 3·51) for the lowest, second and third quartiles, respectively. A similar trend was observed when all-cause mortality was used as the study endpoint. Further analysis showed that the relationships between lower serum Mg and higher risk of cardiovascular and all-cause mortality were present only in the female subgroup, and not among male patients. The test for interaction indicated that the associations between lower serum Mg and cardiovascular and all-cause mortality differed by sex (P=0·008 and P=0·011, respectively). In conclusion, lower serum Mg was associated with a higher risk of cardiovascular and all-cause mortality in the PD population, especially among female patients.

Drug-induced alterations in Mg2+ homoeostasis

Magnesium (Mg2+) balance is tightly regulated by the concerted actions of the intestine, bone and kidneys. This balance can be disturbed by a broad variety of drugs. Diuretics, modulators of the EGFR (epidermal growth factor receptor), proton pump inhibitors, antimicrobials, calcineurin inhibitors and cytostatics may all cause hypomagnesaemia, potentially leading to tetany, seizures and cardiac arrhythmias. Conversely, high doses of Mg2+ salts, frequently administered as an antacid or a laxative, may lead to hypermagnesaemia causing various cardiovascular and neuromuscular abnormalities. A better understanding of the molecular mechanisms underlying the adverse effects of these medications on Mg2+ balance will indicate ways of prevention and treatment of these adverse effects and could potentially provide more insight into Mg2+ homoeostasis.

Magnesium carbonate for phosphate control in patients on hemodialysis. A randomized controlled trial

Background

Magnesium salts bind dietary phosphorus, but their use in renal patients is limited due to their potential for causing side effects. The aim of this study was to evaluate the efficacy and safety of magnesium carbonate (MgCO₃) as a phosphate-binder in hemodialysis patients.

Methods

Forty-six stable hemodialysis patients were randomly allocated to receive either MgCO₃ (n = 25) or calcium carbonate (CaCO₃), (n = 21) for 6 months. The concentration of Mg in the dialysate bath was 0.30 mmol/l in the MgCO₃ group and 0.48 mmol/l in the CaCO₃ group.

Results

Only two of 25 patients (8%) discontinued ingestion of MgCO₃ due to complications: one (4%) because of persistent diarrhea, and the other (4%) because of recurrent hypermagnesemia. In the MgCO₃ and CaCO₃ groups, respectively, time-averaged (months 1–6) serum concentrations were: phosphate (P), 5.47 vs. 5.29 mg/dl, P = ns; Ca, 9.13 vs. 9.60 mg/dl, P < 0.001; Ca × P product, 50.35 vs. 50.70 (mg/dl)², P = ns; Mg, 2.57 vs. 2.41 mg/dl, P = ns; intact parathyroid hormone (iPTH), 285 vs. 235 pg/ml, P < 0.01. At month 6, iPTH levels did not differ between groups: 251 vs. 212 pg/ml, P = ns. At month 6 the percentages of patients with serum levels of phosphate, Ca × P product and iPTH that fell within the Kidney Disease Outcomes Quality Initiative (K/DOQI) guidelines were similar in both groups, whereas more patients in the MgCO₃ group (17/23; 73.91%) than in the CaCO₃ group (5/20, 25%) had serum Ca levels that fell within these guidelines, with the difference being significant at P < 0.01.

Conclusion

Our study shows that MgCO₃ administered for a period of 6 months is an effective and inexpensive agent to control serum phosphate levels in hemodialysis patients. The administration of MgCO₃ in combination with a low dialysate Mg concentration avoids the risk of severe hypermagnesemia.

Inverse correlation between serum magnesium and parathyroid hormone in peritoneal dialysis patients: a contributing factor to adynamic bone disease?

BACKGROUND

Secondary hyperparathyroidism (SHPTH) is present in many patients with end-stage renal disease (ESRD) and has been linked to uremic bone disease. Parathyroid hormone (PTH) levels are affected by calcium, vitamin D, and phosphorus. Recent data suggests that serum magnesium may also modulate PTH levels.

OBJECTIVE

The aim of this retrospective study was to investigate the impact of different calcium (Ca) and magnesium (Mg) concentrations of dialysis solutions on serum Mg and serum PTH levels in peritoneal dialysis (PD) patients.

PATIENTS AND METHODS

Two groups of PD patients-group A (n = 17) on "standard" Ca and Mg dialysis solution (SCa-MgD) (Ca: 1.62 mmol/l, Mg: 0.75 mmol/l and Lactate 35 mmol/l), and group B (n = 29) on "low" Ca and Mg dialysis solution (LCa-MgD) (Ca: 1.25 mmol/l, Mg: 0.25 mmol/l and Lactate 40 mmol/l), on PD for more than 6 months, were studied. Calcium carbonate (CaCO3) was used as the phosphate (P) binder in 87% (40/46) of the patients. Biochemical parameters were evaluated every 1-2 months over 6 months and the mean values were computed.

RESULTS

No significant differences were found between the two groups in all parameters except for serum Mg and PTH. Serum Mg was higher in SCa-MgD group compared to those in the LCa-MgD group (1.05 +/- 0.19 vs 0.90 +/- 0.23 mmol/l, respectively) and serum PTH was higher in LCa-MgD group compared to those in SCa-MgD group (72.3 +/- 64.2 vs 31.1 +/- 39.0 pmol/l, respectively) even though serum Ca was not different. There was a statistically significant inverse correlation between serum Mg and PTH levels (r = -0.357, p < 0.05).

CONCLUSION

Serum Mg is lower and serum PTH higher in patients dialyzed with lower Mg concentration dialysis solution compared to those with higher Mg concentration dialysis solution. Our study confirms previous reports that serum Mg may have a suppressive role on PTH synthesis and/or secretion, and thus may play a role in pathogenesis of adynamic bone disease that often develops in patients on chronic PD with high calcium and high magnesium concentrations.

Acute effects of different concentrations of dialysate magnesium during high-efficiency dialysis

It has been suggested that magnesium carbonate (MgCO3) may be an effective and safe alternative to calcium carbonate in binding phosphorus in dialysis patients. In these studies, the concentration of magnesium in the dialysate was either very low or zero. To date, only patients undergoing conventional dialysis have been reported. The primary purpose of the present study was to determine the fluxes of magnesium using dialysate magnesium concentrations of 0 mg/dL, 0.6 mg/dL, and 1.8 mg/dL in eight patients undergoing high-efficiency hemodialysis. The net removal of magnesium was 486 +/- 44 mg, 306 +/- 69 mg, and 56 +/- 50 mg, with the use of dialysate magnesium concentrations of 0 mg/dL, 0.6 mg/dL, and 1.8 mg/dL, respectively (P = 0.001). Plasma magnesium levels significantly decreased from 3.3 +/- 0.2 mg/dL to 1.6 +/- 0.2 mg/dL and from 3.4 +/- 0.3 mg/dL to 2.1 +/- 0.2 mg/dL during the dialysis sessions using 0 mg/dL and 0.6 mg/dL magnesium dialysates, respectively. Plasma magnesium remained unchanged when 1.8 mg/dL dialysate magnesium was used. A significant independent correlation was found between the total magnesium removed and both the dialysate concentration used (P < 0.001) and the predialysis plasma magnesium level (P < 0.001). The measured magnesium removal exceeded the estimated predialysis extracellular fluid (ECF) magnesium pool with the use of magnesium-free dialysate. This was not found with dialysate magnesium concentrations of either 0.6 mg/dL or 1.8 mg/dL. A secondary purpose of the study was to determine the acute clinical tolerance of the low and magnesium-free dialysates.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperphosphatemia: its consequences and treatment in patients with chronic renal disease

Control of phosphorus accumulation in chronic renal insufficiency is crucial to the prevention of secondary hyperparathyroidism and metastatic calcification. In early renal failure, calcitriol levels are normal and parathyroid hormone levels are elevated. The phosphorus levels are maintained in the normal range by the phosphaturia induced by hyperparathyroidism. In this situation, dietary phosphorus restriction increases calcitriol levels and suppresses parathyroid hormone secretion. As renal failure progresses into late stages, hyperphosphatemia is evident along with low levels of calcitriol and worsening hyperparathyroidism. Phosphorus restriction will not affect calcitriol concentrations, yet parathyroid levels may decline. During long-term dialysis, urinary excretion of phosphorus is usually minimal. Therefore, phosphorus balance is determined primarily by the net amount absorbed by the bowel and the quantity removed during dialytic therapy. Given an adequate diet, no form of conventional dialysis is able to fully compensate for the gastrointestinal absorption of phosphorus. Hence, compounds that bind phosphorus in the bowel are often necessary. With the realization that the use of phosphorus binders containing aluminum leads to aluminum accumulation and its sequelae: osteomalacia, dementia, myopathy, and anemia, other phosphorus binders have been evaluated. Calcium carbonate has been investigated the most thoroughly and is in wide use. It is inexpensive and contains a high percent of elemental calcium. However, it is only modestly potent in the binding of phosphorus, and large doses are often necessary to attain satisfactory control of phosphorus. This may lead to hypercalcemia. One approach to this problem is to decrease the concentration of calcium in the dialysate. Alternatively, a more effective phosphorus binder may be used. Calcium acetate has been shown in acute studies to have twice the binding capacity of phosphorus per calcium absorbed than calcium carbonate. Whether use of this compound decreases the incidence of hypercalcemia is unproven. Calcium citrate increases the gastrointestinal absorption of aluminum and offers no advantage over calcium carbonate. Other compounds, such as calcium ketoacids and calcium alginate, have not been extensively studied and are not generally available. The use of phosphorus binders containing magnesium in conjunction with a dialysate low in magnesium may be efficacious. Large doses of magnesium will cause diarrhea and thus limit its use as a single agent. Reasons for failure to control hyperphosphatemia include poor compliance, improper prescription of binders, poor dissolution rates seen with some generic brands of calcium carbonate, and the presence of severe hyperparathyroidism. Optimal control of serum phosphorus in dialysis patients should always be viewed in the context of adequate nutrition and protein intake.

Colonic intussusception secondary to a calcium phosphate bezoar in a child receiving calcium carbonate for hyperphosphatemia

We report a case of a calcium phosphate bezoar resulting in colonic intussusception in a boy with chronic renal failure who received calcium carbonate to control hyperphosphatemia. Because of concerns about aluminum-related disease in patients receiving aluminum hydroxide phosphate binders, calcium carbonate is being used more frequently to manage phosphate retention in renal failure. The development of bezoars may complicate this new form of therapy.