Inclusion Criteria:

• Male or female subjects on active haemodialysis, aged 18 years or over who are able to comply with study procedures
• Written informed consent given
• On a stable haemodialysis regimen (three times per week) for at least 3 months and be unlikely to change their dialysis prescription during the study period
• On a stable dose of phosphate binder for at least 1 month prior to screening
• Willing to abstain from taking any phosphate binder or oral magnesium-, aluminium- or iron-containing products and preparations, other than the study medication
• Willing to avoid any intentional changes in diet such as fasting, dieting or overeating
• On a dialysate magnesium ion concentration of ≤1.0 mmol/L for at least 1 month prior to screening

Exclusion Criteria:

• Received a cardiac transplant
• Heart failure according to New York Heart Association (NYHA) Functional IV Classification
• Participation in any other clinical trial using an investigational product or device within the previous 4 weeks
• A significant history of alcohol, drug or solvent abuse in the opinion of the investigator
• Any disease or condition, physical or psychological, which in the opinion of the investigator would compromise the safety of the subject or increase the likelihood of the subject being withdrawn
• Clinically significant laboratory findings (at screening for this subject population) in the opinion of the investigator
• Any history of recent clinically significant malignancy
• A significant illness (excluding renal disease) in the 4 weeks before screening
• A history of poorly controlled epilepsy
• Female subjects who are lactating or pregnant. Women of childbearing potential (pre-menopausal and not surgically sterilised) unless they are using a reliable contraceptive method, that is, barrier methods, hormones or intrauterine device
• Allergy to magnesium iron hydroxycarbonate or sevelamer or any component of the formulations
• Any condition that affects the reliability of measuring QT interval, for example, an irregular heart rhythm such as atrial fibrillation or frequent ectopic activity