For precautions that should be considered before administration of saline laxatives in patients susceptible to adverse effects, see Cautions: Saline Laxatives, in the Cathartics and Laxatives General Statement 56:12.
Magnesium-containing Saline Laxatives
Magnesium-containing saline laxatives are administered orally in the form of chewable tablets, suspensions, or solutions.215,216,217,218,222,223,224,225,232 A full (240 mL) glass of liquid should be ingested following administration of each dose.215,216,217,218,224,225,233
Magnesium citrate oral solution may be chilled prior to administration.222
Magnesium hydroxide suspension should be shaken well before each use.215,216,218 The fixed combination of magnesium hydroxide and mineral oil typically is administered at bedtime and should not be administered with meals.218
Magnesium sulfate oral solution may be prepared by dissolving an appropriate dose of the crystals in at least 240 mL of water; lemon juice may be added to improve taste.225 Each level teaspoonful of magnesium sulfate crystals provides approximately 5 g of the drug and 495 mg (40.7 mEq) of magnesium.225
Phosphate-containing laxatives are administered orally as solutions or tablets and rectally as enemas in combinations containing dibasic sodium phosphate and monobasic sodium phosphate;212,213,219,220,221,227,228,229,230 commercially available phosphate-containing laxatives intended for rectal use (i.e., enema solutions) are not intended for oral administration.219,227,228
When sodium phosphates are administered orally as solutions or tablets, a full (240 mL) glass of clear liquid (e.g., water) should be ingested following administration of each dose.275,283 Sodium phosphates tablets should be used with caution in patients with impaired gag reflex and those prone to regurgitation or aspiration; these patients should be observed during administration of sodium phosphates tablets.283
When sodium phosphates are administered rectally as enemas, additional liquid should be ingested during therapy to ensure adequate hydration.280
Phosphate-containing enemas should be administered at room temperature.219 The protective shield (if present) should be removed from the tip of the enema.219,228 For administration of the enema, patients should be advised to lie on their left side with knees bent or to kneel on the bed with the head and chest lowered and forward until the left side of the face is resting on the surface of the bed.219,228 The enema nozzle should be inserted into the rectum with steady pressure and a slight side-to-side movement; the nozzle should be pointed toward the navel.219,228 To ease insertion, the patient should be advised to bear down as if having a bowel movement.219,228 The nozzle should not be forced into the rectum as this can cause injury.219,228 The container should be squeezed until nearly all of the liquid is expelled;219,228 it is not necessary to empty the container as it contains more liquid than needed.228 The nozzle should then be removed from the rectum, and the patient should be advised to maintain the position until the urge to evacuate is strong (usually within 1-5 minutes).219,228
For children 2-4 years of age, an enema containing dibasic sodium phosphate 1.75 g and monobasic sodium phosphate 4.75 g in approximately 29 mL can be prepared for administration as follows.227 The cap of a pediatric-strength enema containing dibasic sodium phosphate 3.5 g and monobasic sodium phosphate 9.5 g in 59 mL (e.g., Fleet® Pedia-Lax® Enema) can be unscrewed and 30 mL of solution removed.227 The cap should then be replaced and the enema administered as directed.227
When used as a laxative for self-medication of occasional constipation, oral solutions of dibasic sodium phosphate and monobasic sodium phosphate should be diluted before administration by adding the appropriate dose of the solution to 240 mL of cool water.275
When used as a purgative in a bowel cleansing regimen prior to surgery or radiographic or endoscopic examination of the colon, oral solutions of dibasic sodium phosphate and monobasic sodium phosphate should be diluted before administration, as directed by a clinician. FDA states that nonprescription (over-the-counter, OTC) oral sodium phosphates preparations (e.g., oral solutions) should be used for bowel cleansing only when a prescription for such use has been issued by a clinician.239,240 (See Sodium Phosphates Oral Solution under Dosage: Bowel Cleansing, in Dosage and Administration.)
Carbon Dioxide-releasing Laxatives
Carbon dioxide-releasing suppositories (e.g., CEO-TWO®) are administered rectally.214 Prior to insertion into the rectum, the wrapper should be removed, and the suppository should be moistened under a warm-water tap for 30 seconds or in a cup of water for at least 10 seconds.214,231,234 Mineral oil or petroleum jelly should not be used to lubricate these suppositories.214,231,234
Saline laxatives should be administered only at infrequent intervals. Most studies suggest that the minimum effective oral laxative dose of magnesium is 80 mEq. The usual dosages of the various saline laxatives are below; for dosages in children younger than the ages listed, a physician should be consulted.
The manufacturers state that laxatives should not be used for self-medication of constipation for longer than 7 days without consulting a clinician.214,215,216,217,218,219,220,221,223,225,231,232,234 FDA states that sodium phosphates preparations should not be used for self-medication of occasional constipation for longer than 3 days.279
The recommended oral dosage of magnesium citrate for self-medication of occasional constipation in adults and children 12 years of age and older is 8.75-25 g (usually 150-300 mL [8.75-17.5 g] of a 291-mg/5-mL oral solution224 ) daily given as a single dose or in divided doses.234 The recommended oral dosage for self-medication in children 6-11 years of age is 5.5-12.5 g (usually 90-150 mL [5.25-8.75 g] of a 291-mg/5-mL oral solution224 ) daily given as a single dose or in divided doses.234 The recommended oral dosage for self-medication in children 2-5 years of age is 2.7-6.25 g (usually 60-90 mL [3.5-5.25 g] of a 291-mg/5-mL oral solution224 ) daily given as a single dose or in divided doses.234
The usual oral dosage of magnesium hydroxide for self-medication of occasional constipation is 2.4-4.8 g daily in adults and children 12 years of age and older,215,216,217,218,233,234 1.2-2.4 g daily in children 6-11 years of age,215,216,217,218,233,234,235 and 0.4-1.2 g daily in children 2-5 years of age.217,233,234,235 The usual dosage should be given as a single dose (preferably at bedtime), in divided doses, or as directed by a clinician.215,216,217,218,233,234
The usual oral dosage of magnesium sulfate for self-medication of occasional constipation is 10-30 g daily in adults and children 12 years of age and older, 5-10 g daily in children 6-11 years of age, and 2.5-5 g daily in children 2-5 years of age.225,234 The usual dosage may be given as a single dose or in divided doses.225,234
When administered as an oral solution for self-medication of occasional constipation, the usual oral dosage in adults and children 12 years of age and older is dibasic sodium phosphate 2.7 g and monobasic sodium phosphate 7.2 g given as a single daily dose; the maximum dosage is dibasic sodium phosphate 8.1 g and monobasic sodium phosphate 21.6 g given as a single daily dose.275 The usual and maximum oral dosage for self-medication in children 10-11 years of age is dibasic sodium phosphate 2.7 g and monobasic sodium phosphate 7.2 g given as a single daily dose.275 The usual and maximum oral dosage for self-medication in children 5-9 years of age is dibasic sodium phosphate 1.35 g and monobasic sodium phosphate 3.6 g given as a single daily dose.275 The manufacturer states that nonprescription oral sodium phosphates preparations (e.g., oral solutions) should not be used for self-medication of occasional constipation in children 5 years of age or younger;275 FDA states that clinicians should be cautious in recommending use of these preparations in this patient population.279 FDA also states that nonprescription sodium phosphates preparations should not be used for self-medication of occasional constipation for longer than 3 days.279
When administered as an enema for self-medication of occasional constipation, the usual rectal dosage in adults and children 12 years of age and older is dibasic sodium phosphate 7 g and monobasic sodium phosphate 19 g (one bottle of Fleet® Enema [approximately 118 mL] or Fleet® Enema Extra [approximately 197 mL]) daily given as a single dose.219,228 The usual rectal dosage for self-medication in children 5-11 years of age is dibasic sodium phosphate 3.5 g and monobasic sodium phosphate 9.5 g (one bottle [approximately 59 mL] of Fleet® Pedia-Lax® Enema) daily given as a single dose, or as directed by a clinician.227 The usual rectal dosage for self-medication in children 2-4 years of age is dibasic sodium phosphate 1.75 g and monobasic sodium phosphate 4.75 g (one-half of a bottle [approximately 29 mL] of Fleet® Pedia-Lax® Enema) daily given as a single dose.227 The manufacturer and FDA state that nonprescription rectal sodium phosphates preparations should not be used for self-medication of occasional constipation in children younger than 2 years of age.279 FDA also states that these preparations should not be used for self-medication of occasional constipation for longer than 3 days.279 Caution should be exercised when selecting phosphate-containing enemas since the commercially available enemas are available in various volumes (i.e., adult and pediatric); use of preparations with volumes appropriate for age should be ensured in order to minimize the risk of overdosage.219,227,228
Severe dehydration, electrolyte abnormalities (e.g., hypernatremia, hyperphosphatemia, hypocalcemia), acute kidney injury, cardiac arrhythmias, and/or death have been reported rarely in adults and children receiving nonprescription sodium phosphates preparations (i.e., oral solution, enema) for self-medication of occasional constipation.279 The majority of reported adverse events occurred in patients who received higher than recommended dosages in a 24-hour period (i.e., a single dose that was larger than recommended or more than one dose in a day) or in patients at increased risk of developing sodium phosphate-induced toxicity.279 Therefore, FDA states that the maximum recommended oral or rectal dosage of nonprescription sodium phosphates preparations should not be exceeded, and that additional doses are not recommended within 24 hours, even in patients who do not have a bowel movement after receiving a dose.279 FDA also states that clinicians should be cautious in recommending use of nonprescription sodium phosphates preparations in patients older than 55 years of a patients with hypovolemia, decreased intravascular volume, kidney disease, decreased bowel transit time, or active colitis; and patients receiving drugs that affect renal perfusion or function (e.g., diuretics, angiotensin converting-enzyme [ACE] inhibitors, angiotensin II receptor antagonists, nonsteroidal anti-inflammatory agents [NSAIAs]).279 FDA recommends that serum electrolytes and renal function be assessed in patients who may be at increased risk of serious adverse effects, including those who have retained a rectal dose for more than 30 minutes, who are vomiting, or who may have signs of dehydration.279 Patients should be advised to discontinue sodium phosphates therapy and to immediately seek medical attention if symptoms of kidney injury (e.g., drowsiness; sluggishness; decreased urine; swelling of the ankles, feet, or legs) occur.279 Nonprescription sodium phosphates preparations should not be used concomitantly with other laxatives containing sodium phosphate.279 For further information on adverse effects associated with sodium phosphates preparations, see Cautions: Saline Laxatives in the Cathartics and Laxatives General Statement 56:12.
Carbon Dioxide-releasing Laxatives
The usual rectal dosage for self-medication of occasional constipation in adults and children 12 years of age and older is 1 suppository (0.9 g of potassium bitartrate and 0.6 g of sodium bicarbonate) daily given as a single dose.214,231,234
When the fixed-combination oral tablets (OsmoPrep®) containing 0.398 g of dibasic sodium phosphate and 1.102 g of monobasic sodium phosphate are used to empty the bowel prior to colonoscopy, tablets should be taken in 2 regimens, one on the night before and one on the day of the procedure.
On the night before the procedure, 1.592 g of dibasic sodium phosphate and 4.408 g of monobasic sodium phosphate (4 tablets) should be taken with at least 240 mL of a clear liquid every 15 minutes until a total dose of 7.96 g of dibasic sodium phosphate and 22.04 g of monobasic sodium phosphate (total of 20 tablets) has been ingested. On the day of the procedure (starting 3-5 hours before the procedure), 1.592 g of dibasic sodium phosphate and 4.408 g of monobasic sodium phosphate (4 tablets) should be taken with at least 240 mL of a clear liquid every 15 minutes until a total dose of 4.776 g of dibasic sodium phosphate and 13.224 g of monobasic sodium phosphate (total of 12 tablets) has been ingested. Total dosage of the 2 regimens is 12.736 g of dibasic sodium phosphate and 35.264 g of monobasic sodium phosphate (32 tablets).
When sodium phosphates is administered rectally as an enema for bowel cleansing prior to rectal examinations, the usual dosage for self-medication in adults and children 12 years of age and older is dibasic sodium phosphate 7 g and monobasic sodium phosphate 19 g (one bottle of Fleet® Enema [approximately 118 mL] or Fleet® Enema Extra [approximately 197 mL]) daily given as a single dose.219,228,281 The usual rectal dosage for self-medication in children 5-11 years of age is dibasic sodium phosphate 3.5 g and monobasic sodium phosphate 9.5 g (one bottle [approximately 59 mL] of Fleet® Pedia-Lax® Enema) daily given as a single dose, or as directed by a clinician.227,281 The usual rectal dosage for self-medication in children 2-4 years of age is dibasic sodium phosphate 1.75 g and monobasic sodium phosphate 4.75 g (one-half bottle [approximately 29 mL] of Fleet® Pedia-Lax® Enema) daily given as a single dose.227,281
Sodium Phosphates Oral Solution
When sodium phosphates oral solution is used as a purgative in a bowel cleansing regimen prior to surgery or radiographic or endoscopic examination of the colon, dosage of the oral solution should be prepared and administered as directed by a clinician.
Use of sodium phosphates oral solution for self-medication for bowel cleansing prior to surgery or radiographic or endoscopic rectal examinations221,229,230 rarely has resulted in fluid shifts, severe electrolyte abnormalities, cardiac arrhythmias, renal failure, acute phosphate nephropathy, generalized tonic-clonic seizures, loss of consciousness, and/or death.212,213 Therefore, in December 2008, FDA stated that oral sodium phosphates preparations should be used for bowel cleansing only when a prescription for such use has been issued by a clinician.239,240 FDA and some manufacturers of oral sodium phosphates preparations recommended that baseline and postprocedural (e.g., postcolonoscopy) laboratory measurements (i.e., serum concentrations of calcium, phosphate, potassium, sodium, creatinine, and BUN) be obtained in patients who may be at increased risk of serious adverse effects, including those with a history of renal impairment, history of acute phosphate nephropathy, known or suspected electrolyte disorders, seizures, arrhythmias, cardiomyopathy, prolonged QT interval, recent myocardial infarction, or known or suspected hyperphosphatemia, hypocalcemia, hypokalemia, or hypernatremia.212,213,236,237,238,239 In addition, postprocedural laboratory measurements should be obtained in patients with vomiting or signs of dehydration.212,213 FDA also recommended monitoring of the glomerular filtration rate in smaller, frail patients.239 Baseline and postprocedural ECGs should be considered in patients at high risk for serious cardiac arrhythmias.212,213
Despite efforts to inform healthcare professionals and consumers about the risks associated with the use of sodium phosphates oral solution for bowel cleansing, FDA continued to receive reports of acute kidney injury (some resulting in kidney transplantation, dialysis, long-term renal failure, and, rarely, death) following administration of usual recommended dosages of the drugs for self-medication for bowel cleansing (approximately 60 g of sodium phosphates [dibasic sodium phosphate and monobasic sodium phosphate salts] administered as two 45-mL doses given 12 hours apart or approximately 50 g of sodium phosphates administered as a 45-mL dose initially, followed by a 30-mL dose 10-12 hours later).239,282 Therefore, as part of its ongoing review of over-the-counter drug products, FDA has tentatively concluded that the usual recommended dosage of nonprescription oral sodium phosphates for self-medication for bowel cleansing based on professional labeling in an OTC monograph poses an unacceptable risk of serious adverse events.282 In February 2011, the agency issued a proposed rule amending the tentative final monograph on nonprescription laxative drug products to classify the individual sodium phosphate salts (i.e., dibasic sodium phosphate, monobasic sodium phosphate) as not generally recognized as safe (GRAS) for bowel cleansing.282 In the proposed rule, FDA also suggested that the professional labeling for sodium phosphates (which discusses use of the drugs as part of a bowel cleansing regimen) be removed from the 1985 tentative final monograph for over-the-counter laxative drug products.282 In response to FDA's proposed rule, some manufacturers have removed the indication for bowel cleansing from labeling of nonprescription sodium phosphates preparations.275 For further information on adverse effects associated with sodium phosphates preparations, see Sodium Phosphates Preparations under Cautions: Saline Laxatives in the Cathartics and Laxatives General Statement 56:12.