We investigated the safety and efficacy of magnesium hydroxide as a phosphate binder in patients with end-stage renal disease on maintenance hemodialysis. 9 volunteers participated in a four-phase study during which each ingested (1) no phosphate binders, (2) magnesium hydroxide (Mg(OH)₂) alone, (3) Mg(OH)₂ and aluminum hydroxide (Al (OH)₃) together and (4) Al(OH)₃ alone. Serum magnesium (SMg) concentrations were maintained at less than 4.5 mEq/l (2.3 mmol/l) in all subjects while they were ingesting 0.75–3 g Mg(OH)₂/day and no magnesium toxicity was noted. In individuals taking a constant daily dose, SMg remained stable over 8–12 weeks. Serum phosphorus (SP) decreased from 9.0 mg/dl (2.9 mmol/l) during the control period to 8.1 mg/dl (2.6 mmol/l) during the Mg(OH)₂ period (p < 0.05) and increased from 6.1 mg/dl (2.0 mmol/l) during the Mg(OH)₂ and Al(OH)₃ period to 7.0 mg/dl (2.3 mmol/l) during the Al(OH)₃ period (p < 0.05) indicating that Mg(OH)₂ could significantly lower SP. However, SP was best controlled (6.1 mg/dl; 2.0 mmol/l) when Al(OH)₃ and Mg(OH > 2 were used together and all participants preferred the combination therapy to either of the agents alone. These results indicate that Mg(OH)₂ is a potentially useful adjunct to Al(OH)₃ for managing hyperphosphatemia in patients on maintenance hemodialysis. In this short-term study Mg(OH)₂ was well tolerated and with appropriate monitoring did not cause uncontrolled hypermagnesemia. Further studies are clearly required to determine whether long-term therapy with Mg-containing agents is safe in dialysis patients.

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