sodium acid phosphate (OsmoPrep, Phospho Soda, sodium biphosphate, sodium phosphate, Visicol): Dosing and Uses

Dosing and uses of OsmoPrep, Phospho Soda (sodium acid phosphate)

• Adult
• Pediatric

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%