What are phosphate agents used in bowel preparation for colonoscopy?

Phosphate Agents Used in Bowel Preparation for Colonoscopy

Phosphate agents for bowel preparation include sodium phosphate solutions, sodium phosphate tablets, and oral sulfate solutions, though sodium phosphate products have significant safety concerns and are no longer first-line options due to risks of acute phosphate nephropathy.

Types of Phosphate Agents

Sodium Phosphate (NaP) Products

• Sodium phosphate solution (Fleet Phospho-Soda): Withdrawn from US over-the-counter market in 2008 due to concerns about phosphate-induced renal disease 1
• Sodium phosphate tablets (Osmo-Prep): Still available by prescription but carries a boxed warning about the risk of acute phosphate nephropathy 1

Oral Sulfate Solution (OSS)

• SUPREP: FDA-approved low-volume phosphate-containing preparation 1
• SUCLEAR: Combination of PEG-ELS and OSS 1

Efficacy of Phosphate Agents

• Sodium phosphate preparations are hyperosmotic cleansing agents that draw water into the bowel lumen to promote evacuation 1
• Studies show that sodium phosphate does not increase bowel cleanliness compared to PEG-ELS (OR, 1.02; 95% CI, 0.77–1.36) but patients are more willing to repeat the regimen (OR, 2.61; 95% CI, 1.48–4.59) 1
• Split-dose regimens of sodium phosphate show better cleansing than single-dose regimens (OR, 2.35; 95% CI, 1.27–4.34) 1
• Ultra-low-volume (<1 L) sodium phosphate regimens have an inadequate bowel preparation rate (82% adequacy rate) 1

Safety Considerations

Major Contraindications for Sodium Phosphate

• Renal insufficiency (creatinine clearance <60 mL/min/1.73 m²) 1
• Pre-existing electrolyte disturbances 1
• Congestive heart failure (New York Heart Association class III or IV or ejection fraction <50%) 1
• Advanced liver disease 2

Adverse Effects

• Electrolyte abnormalities (hypocalcemia, hypokalemia, hyperphosphatemia) 3
• Acute phosphate nephropathy (kidney injury) 1
• Fluid shifts that can exacerbate underlying conditions 1, 4

Alternative Bowel Preparation Agents

Polyethylene Glycol-Electrolyte Lavage Solution (PEG-ELS)

• High-volume (4L): GoLYTELY, Colyte, Gavilyte, NuLYTELY 1
• Low-volume (2L): MoviPrep (PEG-ELS with ascorbate) 1
• Safer option for patients with comorbidities as it is iso-osmolar and isotonic 1

Sodium Picosulfate

• Often combined with magnesium citrate (Prepopik) 1
• Not superior to sodium phosphate in efficacy (OR, 0.60; 95% CI, 0.22–1.65) 1

Recommendations for Clinical Practice

1. For most patients: PEG-ELS preparations are preferred due to their safety profile, particularly in split-dose regimens 1

2. For patients with good renal function and no contraindications: Oral sulfate solution (SUPREP) can be considered as it shows good efficacy in split-dose regimens with a 92% rate of adequate bowel preparation 1

3. Avoid sodium phosphate preparations in:

   • Patients with renal insufficiency 1
   • Patients with electrolyte disturbances 1
   • Patients with heart failure 1
   • Elderly patients (higher risk of adverse events) 1

Important Clinical Pearls

• Always assess renal function before prescribing phosphate-based bowel preparations 1
• Ensure adequate hydration before, during, and after phosphate-based preparations to reduce risk of renal injury 5
• Monitor electrolytes in high-risk patients receiving phosphate preparations 4
• Split-dose regimens provide superior bowel cleansing compared to day-before regimens for all preparation types 1

Despite their efficacy and patient preference, sodium phosphate agents should not be used as first-line bowel preparation agents due to safety concerns. PEG-based preparations remain the safest option for most patients, especially those with comorbidities.