Published: May 2009

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Phosphate containing laxatives - hyperphosphataemia and kidney damage

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Prescriber Update 30(2): 8
May 2009

Medsafe would like to draw prescribers attention to evidence of an increased risk of acute renal failure due to the use of oral phosphate containing laxatives prior to colonoscopy.

Adverse reaction reports include end stage renal failure (requiring dialysis) and renal failure resulting in death.

The Medicines Adverse Reactions Committee (MARC) reviewed this issue at its December 2008 meeting and considers that significant risks exist, particularly renal damage and electrolyte imbalances such as hyperphosphataemia, hypokalaemia and hypocalcaemia. The MARC noted that renal damage typically takes the form of phosphate nephropathy.

The Fleet Phospho-soda Bufffered Saline Mixture is the only phosphate containing oral laxative approved in New Zealand and its data sheet includes the following contraindications:

• Clinically significant impairment of renal function and potentially pre-existing fluid/electrolyte disturbances.
• Patients at risk of dehydration due to altered senses and/or poor fluid intake.

Risk factors for the development of renal damage following colonoscopy include prior dehydration and comorbid conditions such as hypertension, congestive cardiac failure, diabetes mellitus, liver and renal impairment. Medicines that may predispose patients to phosphate nephropathy include non-steroidal anti-inflammatory drugs (NSAIDs), angiotensin converting enzyme inhibitors (ACEI), angiotensin receptor blockers (ARB), and diuretics.

In order to reduce the risk of dehydration and hyperphosphataemia patients should be encouraged to drink large quantities of fluid during bowel preparation (approximately 750 mL of clear liquid per 45 mL dose followed by 750 mL over the next 10-12 hours).

Products containing alternative active ingredients should be considered for bowel preparation in patients at risk, the elderly and others unlikely to be able to maintain hydration.

Prescribers should consider steps to maintain hydration in at risk patients and may need to monitor renal function and electrolytes.

This risk is discussed in more detail by Markowitz et al (2005)¹.

Reference

1. Markowitz et al. 2005.Acute Phosphate Nephropathy following Oral Sodium Phosphate Bowel Purgative: An Underrecognized Cause of Chronic Renal Failure.2005.Journal of the American Society of Nephrology, 16:3389-96