sodium acid phosphate (OsmoPrep, Phospho Soda, sodium biphosphate, sodium phosphate, Visicol)
Classes: Laxatives, Saline
Dosing and uses of OsmoPrep, Phospho Soda (sodium acid phosphate)
Adult dosage forms and strengths
aqueous solution
- Na2HPO4/NaH2PO4
- (48g/18g)/100mL
tablet
- Na2HPO4/NaH2PO4
- 0.398g/1.102g
enema
- Na2HPO4/NaH2PO4
- (7g/19g)/118mL
Bowel Preparation for Colonoscopy
OsmoPrep: 4 tablets with 8 oz of water PO q15min (total 20 tablets) evening before procedure, & repeat regimen (12 tablets) next day 3-5 hours before procedure
Visicol: 3 tablets with 8 oz of water PO q15min (last dose 2 tablets, total 20 tablets) evening before procedure, & repeat same regimen next day 3-5 hours before procedure
Aqueous: 30-45 mL (of 48 g Na2HPO4-18 g NaH2PO4/100 mL) PO x2 10-12 hours apart; each dose with at least 8 oz liquid; each dose followed by additional minimum 16 oz liquid; 2nd dose at least 3 hours before procedure
Laxative
PR: Administer contents of 4.5 oz enema rectally as single dose
PO: Administer 15 mL as single dose qDay; not to exceed 45 mL/day
Pediatric dosage forms and strengths
aqueous solution
- Na2HPO4/NaH2PO4
- (48g/18g)/100mL
tablet
- Na2HPO4/NaH2PO4
- 0.398g/1.102g
enema
- Na2HPO4/NaH2PO4
- (7g/19g)/118mL
pediatric enema
- Na2HPO4/NaH2PO4
- (3.5g/9.5g)/59mL
Bowel Preparation for Colonoscopy (No Standard Regimen; One Recommended)
<15 kg: 22.5 mL aqueous PO afternoon & evening before colonoscopy
≥15 kg: 45 mL aqueous PO afternoon & evening before colonoscopy
Laxative (Rectal)
<2 years: Safety & efficacy not established
2-4 years: Administer one half content of 2.25 oz pediatric enema as single dose
4-12 years: Administer contents of 2.25 oz pediatric enema as single dose
≥12 years: Administer contents of 4.5 oz enema rectally as single dose
Laxative (Oral)
<5 years: Safety and efficacy not established
5-10 years: 7.5 mL as single dose; not to exceed 7.5 mL/day
10-12 years: 15 mL as single dose; not to exceed 15 mL/day
≥12 years: 15 mL as single dose qDay; not to exceed 45 mL/day
OsmoPrep, Phospho Soda (sodium acid phosphate) adverse (side) effects
Frequency not defined
Possible QT interval prolongation due to electrolyte imbalance
Aspiration
Dizziness
Headache
Abdominal pain
Vomiting
Mucosal bleeding
Bloating
Colonic mucosal ulceration
Nausea
Electrolyte imbalance: hyperphosphatemia, hypocalcemia, hypernatremia, hypokalemia
Metabolic acidosis, dehydration
Acute phosphate nephropathy
Cardiac arrythmia
Facial edema
Warnings
Black box warnings
Rare reports of acute phosphate nephropathy with oral sodium phosphate products used for colon cleansing before colonoscopy
Some cases have resulted in permanent renal function impairment requiring long-term hemodialysis
Risk factors for acute phosphate nephropathy include age >55 yr, hypovolemia, baseline kidney disease, bowel obstruction, active colitis, and those using medicines that affect renal perfusion or function (eg, diuretics, ACE inhibitors, ARBs, NSAIDs)
Carefully follow dosing regimen as recommended (pm/am split dose) with adequate hydration
Contraindications
Enema: Renal failure, CHF, ascites, obstruction, megacolon, perforated bowel, ulcerative colitis, fecal impaction
IV: Hyperphosphatemia, hypocalcemia, hypernatremia
Oral: Bowel obstruction, bowel perforation, gastric bypass, toxic colitis, toxic megacolon, acute phosphate nephropathy
Cautions
Should not be readministered for at least 7 days
Risk of acute phosphate nephropathy
Osmotic laxative products may produce colonic mucosal ulcerations, and there have been reports of more serious cases of ischemic colitis requiring hospitalization
QT interval prolongation reported
Use caution in heart failure, unstable angina, cardiomyopathy, patients at risk for arrhythmias, patients with pre-existing electrolyte disturbances, gastric retention or hypomotility, severe chronic constipation, colitis, or ileus, chronic inflammatory bowel disease, or history of seizures
Severe dehydration and electrolyte abnormalities associated with serious complications (eg, acute kidney injury, arrhythmias, and death) have occurred in adults and children who overdosed using oral or rectal over-the-counter (OTC) sodium phosphate solutions to treat constipation
Pregnancy and lactation
Pregnancy category: C
Lactation: Use caution
Pregnancy categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA: Information not available.
Pharmacology of OsmoPrep, Phospho Soda (sodium acid phosphate)
Mechanism of action
Draws water into the lumen of the gut where it causes osmotic effect; causes abdominal distention and promotes peristalsis and evacuation of the boweL
Pharmacokinetics
Onset: 2-5 min (rectal); 3-6 hr (cathartic)
Absorption: 1-20%
Excretion: Urine: 90%