Magnesium citrate is a hyperosmotic saline laxative given orally as a bowel preparation prior to intestinal surgery/procedures or for intermittent relief of constipation. Magnesium citrate acts by osmotically drawing water into the intestinal lumen; the intestine then responds to the increase in volume with increased peristalsis and release of cholecystokinin. The onset of laxative effect is short (30 minutes-4 hours) for magnesium citrate and other saline laxatives. Because of the potential for serious magnesium toxicity in patients with renal impairment, polyethylene glycol (PEG) solution may be a preferred agent over magnesium citrate in these patients prior to GI procedures or surgery (see Polyethylene glycol; Electrolytes monograph). Magnesium citrate is also used for short-term, acute treatment of constipation, but is not recommended for routine use. The drug is only rarely used for magnesium supplementation, and is not normally recommended for this purpose. Magnesium citrate oral solutions have been used clinically for decades.
General Administration Information
For storage information, see the specific product information within the How Supplied section.
Route-Specific Administration
Oral Administration
-Administer orally in a fasting state, unless otherwise directed. Typically, for bowel catharsis, no solid food should be consumed until after the GI procedure is complete.
-Due to the short onset time for laxative effect (generally 30 minutes-4 hours), administration late in the day or at bedtime is not generally recommended.
Oral Liquid Formulations:
-Magnesium citrate has a bitter taste and is more palatable if chilled before administration. Lemon or other citrus juice may be added to the solution to reduce the bitter taste, if allowable given any dietary restrictions of the preparative regimen.
-Magnesium citrate oral solution should be taken with 1-2 glasses of water to assure stool passage into the intestine.
In general, saline laxatives such as oral magnesium citrate solution do not cause serious adverse reactions, unless used chronically or taken in overdose amounts. The most common adverse reaction with oral magnesium citrate is diarrhea, an expected side effect. Nausea and vomiting may occur in some patients due to the bitter taste of the citrate solution. Magnesium citrate can be chilled and mixed with lemon juice or other fruit juices to help mask the objectionable taste. Skin irritation in the rectal area has been reported following use.
Dehydration or electrolyte imbalance may occur with chronic use or abuse of saline laxatives. Electrolyte imbalance, including magnesium toxicity, may occur in patients with renal impairment. Hypermagnesemia symptoms such as flushing, diaphoresis, ECG changes, hypotension, sedation (drowsiness) and confusion may occur when plasma magnesium concentrations reach 1.5-2.2 mEq/L. At plasma magnesium concentrations >= 4.4 mEq/L deep tendon reflexes may become depressed, resulting in muscle weakness and hyporeflexia; patellar reflexes may disappear at magnesium concentrations > 8 mEq/ml. Respiratory depression or respiratory arrest may occur at concentrations > 12-14 mEq/L. AV block, complete heart block or cardiac arrest may occur at high concentrations, >= 15 mEq/L. Magnesium toxicity (conduction abnormalities or respiratory depression) can be reversed by discontinuation of therapy and the use of intravenous calcium gluconate. Dehydration, due to diarrhea or the hyperosmotic effects of magnesium citrate solution may be a factor; dehydration can further negatively impact fluid and electrolyte balance.
Magnesium citrate is contraindicated in any patient with a known hypersensitivity to the drug or any of its components.
Magnesium citrate solution contains 290 mg of magnesium and 80 mg of potassium per 1 fl oz (30 ml). Patients on a magnesium or potassium restricted diet should consult their healthcare provider before taking magnesium citrate cathartics. Magnesium citrate should not be used in any patient with hypermagnesemia. It should not be used in patients with severe renal impairment, renal failure, or renal disease leading to renal failure. Individuals with renal impairment should not be given more than 50 mEq/dose of magnesium unless under the specific direction of a health care professional equipped to monitor electrolytes. In patients with impaired renal function, oral administration of >/= 30 g (243 mEq) of magnesium has been fatal. Use with extreme caution, if at all, in patients with CrCl < 30 ml/min. Also, use magnesium citrate cautiously in patients taking digoxin or other cardiac glycosides, as altered magnesium levels may lead to cardiac conduction abnormalities and possible heart block. The risk of cardiotoxicity due to hypermagnesemia is also elevated in the presence of hypocalcemia, hyperkalemia, and metabolic acidosis. Monitor magnesium levels carefully if indicated in patients with cardiac disease.
Saline cathartics, such as magnesium citrate, should not be used in patients with a history of acute abdominal pain, appendicitis, colitis, colostomy, diabetes mellitus, diverticulitis, fecal impaction, GI obstruction, GI perforation, ileostomy, ileus, toxic megacolon, or vomiting. Magnesium citrate is contraindicated in the presence of rectal GI bleeding. Patients who develop GI bleeding while taking magnesium citrate should discontinue use of the product and seek medical attention. Likewise, patients should stop use and consult a physician if magnesium citrate fails to produce a bowel movement as this may be a sign of a more serious GI problem; a bowel movement should occur between 1/2 to 6 hours after the administration of magnesium citrate solution. Magnesium citrate solution should not be used to treat chronic constipation due to the potential for electrolyte imbalance and dehydration. When used for as a cathartic, magnesium citrate solution should be administered with plenty of fluids to avoid dehydration that may occur due to the hyperosmotic solution. In addition, advise patients to consult their healthcare professional before starting laxative treatment with magnesium citrate solution if they have experienced a sudden change in bowel habits lasting more than 2 weeks or if they have been using a different laxative for more than a week.
Due to age-related changes in renal function, magnesium citrate should be used cautiously in geriatric adults. It may be advisable to assess renal function prior to magnesium citrate administration.
Neonates, infants and children under 6 years should only be given hyperosmotic saline laxatives under the supervision of a physician.
Oral magnesium citrate is classified in FDA pregnancy risk category B. However, oral magnesium citrate solution should be used during pregnancy only if clearly needed. Occasional use is acceptable during pregnancy; however, indiscriminate or long-term use can result in hypermagnesemia, hyperphosphatemia, and dehydration. Magnesium is found in formulations of prenatal vitamins and when taken in normal dietary amounts is not considered harmful. However, use of magnesium containing medications should occur under medical supervision in pregnancy. Magnesium citrate, especially if it is being used as a laxative, should not be taken without a prescription during pregnancy; avoid non-prescription use. The safest first-line treatments to use for constipation during pregnancy are those that are not absorbed systemically (e.g., fiber, bulk-forming laxatives) or those with minimal risk, such as stool softeners.
Problems with magnesium citrate use during breast-feeding have not been demonstrated with normally recommended doses for occasional use. Intravenous magnesium therapy only increases magnesium concentrations in human milk slightly, and oral magnesium products should not raise human milk concentrations much at all, particularly if not used for extended periods.
Oral magnesium citrate solution contains 3.85 to 4.71 mEq of magnesium per 5 mL (roughly 250 mEq magnesium per 300 mL bottle).
For use intermittently as a laxative to treat acute constipation:
Oral dosage (Magnesium Citrate oral solution 1.745 grams/30 mL):
Adults: 150 to 300 mL PO as a single or divided dose. Max: 300 mL/24 hours. Routine use is not recommended. Use only intermittent single doses.
Children and Adolescents 12 to 17 years: 150 to 300 mL PO as a single or divided dose. Max: 300 mL/24 hours.
Children 6 to 11 years: 100 to 150 mL PO as a single or divided dose. Alternatively, administer 90 to 210 mL PO as a single or divided dose. Max: 210 mL/24 hours.
Children 2 to 5 years: 1 to 3 mL/kg/day PO as a single or divided dose. Alternatively, administer 60 to 90 mL PO as a single or divided dose. Max: 90 mL/24 hours. Children younger than 6 years should only be given saline laxatives under the supervision of the prescriber.
For use as a bowel preparation* prior to colonoscopy:
Oral dosage (Magnesium Citrate 1.745 grams/30 mL):
Adults: Not FDA-approved; expert recommendations do not recommend use for routine colonoscopy preparation due to limited efficacy data and potential toxicity. Usual dosage: 300 to 450 mL the day before procedure and 300 to 450 mL the day of procedure. The patient should ingest at least 2 L of water during this preparatory regimen. Not to be used in the elderly or in patients with renal dysfunction.
Therapeutic Drug Monitoring:
-Normal serum magnesium 1.4-2 mEq/L; may vary depending upon laboratory standards.
-Laboratory monitoring: serum magnesium, serum potassium, and serum creatinine.
-Other: deep tendon reflexes, respirations, and urinary output.
Maximum Dosage Limits:
-Adults
300 mL/24 hours PO as a laxative.
-Geriatric
300 mL/24 hours PO as a laxative.
-Adolescents
300 mL/24 hours PO as a laxative.
-Children
12 years: 300 mL/24 hours PO as a laxative.
6 to 11 years: 210 mL/24 hours PO as a laxative.
2 to 5 years: 3 mL/kg/day or 90 mL/24 hours PO as a laxative.
younger than 2 years: Safety and efficacy have not been established.
-Infants
Safety and efficacy have not been established.
Patients with Hepatic Impairment Dosing
Specific guidelines for dosage adjustments in hepatic impairment are not available; it appears that no dosage adjustments are needed.
Patients with Renal Impairment Dosing
Dosage should be modified depending on clinical response and degree of renal impairment, but no quantitative recommendations are available. Individuals with renal impairment should not be given more than 50 mEq/dose of magnesium unless under the specific direction of a health care professional equipped to monitor electrolytes. In patients with impaired renal function, oral administration of >= 243 mEq of magnesium has been fatal.
CrCl >= 25 ml/min: Patients with renal impairment may be at risk of accumulating magnesium. However, no dosage guidelines are available.
CrCl 10-25 ml/min: Patients with renal impairment may be at risk of accumulating magnesium. However, no dosage guidelines are available; serum magnesium monitoring is recommended if magnesium citrate must be used.
CrCl < 10 ml/min: Avoid use in renal failure. If use is necessary, monitor serum magnesium levels. Dosage should be modified depending on clinical response and degree of renal impairment.
*non-FDA-approved indication
Abacavir; Dolutegravir; Lamivudine: (Moderate) Administer dolutegravir 2 hours before or 6 hours after taking cation-containing laxatives such as magnesium citrate. The chemical structure contains polyvalent cations which can bind dolutegravir in the GI tract. Taking magnesium citrate simultaneously may result in reduced bioavailability of dolutegravir.
Acetaminophen; Hydrocodone: (Minor) Concurrent use of hydrocodone with strong laxatives that rapidly increase gastrointestinal motility, such as magnesium citrate, may decrease hydrocodone absorption. Closely monitor patients for changing analgesic requirements or adverse events.
Alendronate: (Moderate) Separate administration of alendronate and magnesium-containing supplements by at least 30 minutes. Magnesium will interfere with the absorption of alendronate.
Alendronate; Cholecalciferol: (Major) Avoid vitamin D coadministration with magnesium citrate in persons on chronic hemodialysis due to the risk for hypermagnesemia. (Moderate) Separate administration of alendronate and magnesium-containing supplements by at least 30 minutes. Magnesium will interfere with the absorption of alendronate.
Atropine; Difenoxin: (Moderate) Diphenoxylate can decrease GI motility. Drugs used to treat constipation, such as laxatives, would counteract the effect of antidiarrheals. In general, it would be illogical to concurrently administer these drugs at the same time. If an antidiarrheal medication is needed, it would be wise to temporarily discontinue use of agents with laxative effects.
Baloxavir Marboxil: (Major) Do not administer baloxavir with products that contain magnesium citrate. Polyvalent cations, such as magnesium, can chelate with baloxavir, reducing its absorption.
Bismuth Subcitrate Potassium; Metronidazole; Tetracycline: (Moderate) Administer magnesium citrate at least 3 hours before or 3 hours after orally administered tetracyclines. Tetracycline absorption may be reduced as tetracycline antibiotics can chelate with divalent or trivalent cations.
Bismuth Subsalicylate; Metronidazole; Tetracycline: (Moderate) Administer magnesium citrate at least 3 hours before or 3 hours after orally administered tetracyclines. Tetracycline absorption may be reduced as tetracycline antibiotics can chelate with divalent or trivalent cations.
Bumetanide: (Moderate) Monitor potassium concentration before and during concomitant laxative, such as magnesium citrate, and loop diuretic use due to risk for additive hypokalemia; potassium supplementation may be necessary.
Cabotegravir: (Moderate) Administer oral magnesium citrate at least two hours before or four hours after taking oral cabotegravir. Magnesium is a polyvalent cation that can bind cabotegravir in the GI tract. Taking these drugs simultaneously may result in reduced oral bioavailability of cabotegravir.
Cabotegravir; Rilpivirine: (Moderate) Administer oral magnesium citrate at least two hours before or four hours after taking oral cabotegravir. Magnesium is a polyvalent cation that can bind cabotegravir in the GI tract. Taking these drugs simultaneously may result in reduced oral bioavailability of cabotegravir.
Calcifediol: (Major) Avoid vitamin D analog coadministration with magnesium citrate in persons on chronic hemodialysis due to the risk for hypermagnesemia.
Calcitriol: (Major) Avoid vitamin D analog coadministration with magnesium citrate in persons on chronic hemodialysis due to the risk for hypermagnesemia.
Calcium Phosphate, Supersaturated: (Moderate) Sodium phosphate monobasic monohydrate; sodium phosphate dibasic anhydrous should not be combined with additional laxatives or purgatives when being used to evacuate the bowel prior to colonic radiologic examinations or surgery.
Calcium; Vitamin D: (Major) Avoid vitamin D coadministration with magnesium citrate in persons on chronic hemodialysis due to the risk for hypermagnesemia.
Calcium; Vitamin D: (Major) Avoid vitamin D coadministration with magnesium citrate in persons on chronic hemodialysis due to the risk for hypermagnesemia.
Chlorpheniramine; Hydrocodone: (Minor) Concurrent use of hydrocodone with strong laxatives that rapidly increase gastrointestinal motility, such as magnesium citrate, may decrease hydrocodone absorption. Closely monitor patients for changing analgesic requirements or adverse events.
Ciprofloxacin: (Moderate) Administer oral ciprofloxacin at least 2 hours before or 6 hours after magnesium citrate. Ciprofloxacin absorption may be reduced as quinolone antibiotics can chelate with divalent or trivalent cations.
Cod Liver Oil: (Major) Avoid vitamin D coadministration with magnesium citrate in persons on chronic hemodialysis due to the risk for hypermagnesemia.
Delafloxacin: (Major) Administer oral delafloxacin at least 2 hours before or 6 hours after products that contain magnesium citrate. Delafloxacin absorption may be reduced as quinolone antibiotics can chelate with divalent or trivalent cations.
Demeclocycline: (Moderate) Administer magnesium citrate at least 3 hours before or 3 hours after orally administered tetracyclines. Tetracycline absorption may be reduced as tetracycline antibiotics can chelate with divalent or trivalent cations.
Dichlorphenamide: (Moderate) Use dichlorphenamide and magnesium citrate together with caution. Dichlorphenamide increases potassium excretion and can cause hypokalemia and should be used cautiously with other drugs that may cause hypokalemia including laxatives. Measure potassium concentrations at baseline and periodically during dichlorphenamide treatment. If hypokalemia occurs or persists, consider reducing the dichlorphenamide dose or discontinuing dichlorphenamide therapy.
Diphenoxylate; Atropine: (Moderate) Diphenoxylate can decrease GI motility. Drugs used to treat constipation, such as laxatives, would counteract the effect of antidiarrheals. In general, it would be illogical to concurrently administer these drugs at the same time. If an antidiarrheal medication is needed, it would be wise to temporarily discontinue use of agents with laxative effects.
Dolutegravir: (Moderate) Administer dolutegravir 2 hours before or 6 hours after taking cation-containing laxatives such as magnesium citrate. The chemical structure contains polyvalent cations which can bind dolutegravir in the GI tract. Taking magnesium citrate simultaneously may result in reduced bioavailability of dolutegravir.
Dolutegravir; Lamivudine: (Moderate) Administer dolutegravir 2 hours before or 6 hours after taking cation-containing laxatives such as magnesium citrate. The chemical structure contains polyvalent cations which can bind dolutegravir in the GI tract. Taking magnesium citrate simultaneously may result in reduced bioavailability of dolutegravir.
Dolutegravir; Rilpivirine: (Moderate) Administer dolutegravir 2 hours before or 6 hours after taking cation-containing laxatives such as magnesium citrate. The chemical structure contains polyvalent cations which can bind dolutegravir in the GI tract. Taking magnesium citrate simultaneously may result in reduced bioavailability of dolutegravir.
Doxercalciferol: (Major) Avoid vitamin D analog coadministration with magnesium citrate in persons on chronic hemodialysis due to the risk for hypermagnesemia.
Doxycycline: (Moderate) Administer magnesium citrate at least 3 hours before or 3 hours after orally administered tetracyclines. Tetracycline absorption may be reduced as tetracycline antibiotics can chelate with divalent or trivalent cations.
Edetate Calcium Disodium, Calcium EDTA: (Major) Administration of oral magnesium citrate with edetate disodium, disodium EDTA may result in binding of magnesium. Do not administer oral magnesium salts within 1 hour of edetate disodium, EDTA.
Ethacrynic Acid: (Moderate) Monitor potassium concentration before and during concomitant laxative, such as magnesium citrate, and loop diuretic use due to risk for additive hypokalemia; potassium supplementation may be necessary.
Etidronate: (Moderate) Do not administer oral magnesium-containing products within 2 hours of oral bisphosphonates; oral magnesium may significantly reduce the absorption of the oral bisphosphonates (e.g., alendronate, etidronate, ibandronate, risedronate, or tiludronate). All medications should be administered at least 30 minutes after an alendronate or risedronate dose, and at least 1 hour after an ibandronate dose to help prevent absorption interactions. Some recommend that divalent cation-containing products should preferentially be taken at least 2 hours after these drugs or at a different time of day.
Furosemide: (Moderate) Monitor potassium concentration before and during concomitant laxative, such as magnesium citrate, and loop diuretic use due to risk for additive hypokalemia; potassium supplementation may be necessary.
Gemifloxacin: (Major) Administer magnesium citrate at least 3 hours before or 2 hours after gemifloxacin. Gemifloxacin absorption may be reduced as quinolone antibiotics can chelate with divalent or trivalent cations.
Homatropine; Hydrocodone: (Minor) Concurrent use of hydrocodone with strong laxatives that rapidly increase gastrointestinal motility, such as magnesium citrate, may decrease hydrocodone absorption. Closely monitor patients for changing analgesic requirements or adverse events.
Hydrocodone: (Minor) Concurrent use of hydrocodone with strong laxatives that rapidly increase gastrointestinal motility, such as magnesium citrate, may decrease hydrocodone absorption. Closely monitor patients for changing analgesic requirements or adverse events.
Hydrocodone; Ibuprofen: (Minor) Concurrent use of hydrocodone with strong laxatives that rapidly increase gastrointestinal motility, such as magnesium citrate, may decrease hydrocodone absorption. Closely monitor patients for changing analgesic requirements or adverse events.
Ibandronate: (Moderate) Do not administer oral magnesium-containing products within 2 hours of oral bisphosphonates; oral magnesium may significantly reduce the absorption of the oral bisphosphonates (e.g., alendronate, etidronate, ibandronate, risedronate, or tiludronate). All medications should be administered at least 30 minutes after an alendronate or risedronate dose, and at least 1 hour after an ibandronate dose to help prevent absorption interactions. Some recommend that divalent cation-containing products should preferentially be taken at least 2 hours after these drugs or at a different time of day.
Lactulose: (Major) In general, other laxatives, such as magnesium citrate, should not be used concurrently with lactulose, especially during the initial phase of therapy for portal-systemic encephalopathy, because the loose stools resulting from their use may falsely suggest that adequate lactulose dosage has been achieved.
Levofloxacin: (Moderate) Administer magnesium citrate at least 2 hours before or 2 hours after orally administered levofloxacin. Levofloxacin absorption may be reduced as quinolone antibiotics can chelate with divalent or trivalent cations. Chelation of divalent cations with levofloxacin is less than with other quinolones.
Loop diuretics: (Moderate) Monitor potassium concentration before and during concomitant laxative, such as magnesium citrate, and loop diuretic use due to risk for additive hypokalemia; potassium supplementation may be necessary.
Minocycline: (Moderate) Administer magnesium citrate at least 3 hours before or 3 hours after orally administered tetracyclines. Tetracycline absorption may be reduced as tetracycline antibiotics can chelate with divalent or trivalent cations.
Moxifloxacin: (Major) Administer oral moxifloxacin at least 4 hours before or 8 hours after magnesium citrate. Moxifloxacin absorption may be reduced as quinolone antibiotics can chelate with divalent or trivalent cations.
Ofloxacin: (Moderate) Administer magnesium citrate at least 2 hours before or 2 hours after ofloxacin. Ofloxacin absorption may be reduced as quinolone antibiotics can chelate with divalent or trivalent cations.
Omadacycline: (Moderate) Administer magnesium citrate at least 3 hours before or 3 hours after orally administered tetracyclines. Tetracycline absorption may be reduced as tetracycline antibiotics can chelate with divalent or trivalent cations.
Paricalcitol: (Major) Avoid vitamin D analog coadministration with magnesium citrate in persons on chronic hemodialysis due to the risk for hypermagnesemia.
Pimozide: (Moderate) According to the manufacturer of pimozide, the drug should not be coadministered with drugs known to cause electrolyte imbalances, such as magnesium citrate when used to cleanse the bowel, except when medically necessary. Pimozide is associated with a well-established risk of QT prolongation and torsade de pointes (TdP), and electrolyte imbalances (e.g., hypokalemia, hypocalcemia, hypomagnesemia) may increase the risk of life-threatening arrhythmias. Pimozide is contraindicated in patients with known hypokalemia or hypomagnesemia.
Risedronate: (Moderate) Do not administer oral magnesium-containing products within 2 hours of oral bisphosphonates; oral magnesium may significantly reduce the absorption of the oral bisphosphonates (e.g., alendronate, etidronate, ibandronate, risedronate, or tiludronate). All medications should be administered at least 30 minutes after an alendronate or risedronate dose, and at least 1 hour after an ibandronate dose to help prevent absorption interactions. Some recommend that divalent cation-containing products should preferentially be taken at least 2 hours after these drugs or at a different time of day.
Sarecycline: (Moderate) Administer magnesium citrate at least 3 hours before or 3 hours after orally administered tetracyclines. Tetracycline absorption may be reduced as tetracycline antibiotics can chelate with divalent or trivalent cations.
Sodium Phosphate Monobasic Monohydrate; Sodium Phosphate Dibasic Anhydrous: (Moderate) Sodium phosphate monobasic monohydrate; sodium phosphate dibasic anhydrous should not be combined with additional laxatives or purgatives when being used to evacuate the bowel prior to colonic radiologic examinations or surgery.
Sodium Polystyrene Sulfonate: (Major) Concurrent use of oral magnesium citrate with sodium polystyrene sulfonate (Kayexalate) is not recommended. Sodium polystyrene sulfonate may bind with magnesium administered orally; however, the risk of binding with oral magnesium may be less with rectal administration of sodium polystyrene sulfonate.
Sulfacetamide; Sulfur: (Major) Administration of oral magnesium citrate with edetate disodium, disodium EDTA may result in binding of magnesium. Do not administer oral magnesium salts within 1 hour of edetate disodium, EDTA.
Tetracycline: (Moderate) Administer magnesium citrate at least 3 hours before or 3 hours after orally administered tetracyclines. Tetracycline absorption may be reduced as tetracycline antibiotics can chelate with divalent or trivalent cations.
Tetracyclines: (Moderate) Administer magnesium citrate at least 3 hours before or 3 hours after orally administered tetracyclines. Tetracycline absorption may be reduced as tetracycline antibiotics can chelate with divalent or trivalent cations.
Torsemide: (Moderate) Monitor potassium concentration before and during concomitant laxative, such as magnesium citrate, and loop diuretic use due to risk for additive hypokalemia; potassium supplementation may be necessary.
Vitamin D analogs: (Major) Avoid vitamin D analog coadministration with magnesium citrate in persons on chronic hemodialysis due to the risk for hypermagnesemia.
Vitamin D: (Major) Avoid vitamin D coadministration with magnesium citrate in persons on chronic hemodialysis due to the risk for hypermagnesemia.
Vitamin D: (Major) Avoid vitamin D coadministration with magnesium citrate in persons on chronic hemodialysis due to the risk for hypermagnesemia.
As a laxative, magnesium citrate exerts its action primarily in the small intestine. The accepted mechanisms include a hyperosmotic effect from magnesium in the small intestine and stimulation of stretch receptors and peristalsis through retention of water. Other evidence indicates, however, that hyperosmolarity does not occur and that cholecystokinin release or decreased transit time are potential contributory mechanisms.
Magnesium is necessary for binding of intracellular macromolecules to organelles and mRNA to ribosomes. Magnesium is also a cofactor to all enzymes involved in phosphate transfer reactions that use ATP and other nucleotides as substrates. Magnesium ions are a cofactor for the normal function of the ATP-dependent sodium-potassium 'pump' found in muscle membranes. Without magnesium, the efficiency of this pump is compromised. Magnesium exhibits the ability to decrease calcium uptake and decrease potassium efflux at the muscle membrane; calcium is a direct antagonist of magnesium.
Magnesium citrate is administered orally in solution. Magnesium is distributed throughout the body. Approximately one-half of the total magnesium in the body is present in soft tissue; most of the remaining magnesium is present in bone. Less than 1% of the total body magnesium is present the blood. Normal serum concentrations range 1.4-2 mEq/L in adults. Magnesium crosses the placenta and is excreted into breast milk; however, problems in humans have not been documented. Magnesium is not metabolized. Elimination occurs renally, but the rate of excretion varies. Approximately 1.5 g (12 mEq) of magnesium is excreted in the urine daily. Magnesium ions are reabsorbed in the thick ascending limb of the loop of Henle.
Affected cytochrome P450 isoenzymes and drug transporters: none
-Route-Specific Pharmacokinetics
Oral Route
Oral administration of magnesium salts results in about 15-30% of a dose being absorbed, probably through active transport. The drug remaining in the GI tract produces a watery stool within 3-6 hours, thereby producing a laxative effect.
-Special Populations
Renal Impairment
Patients with renal impairment exhibit a reduced ability to excrete magnesium. Magnesium accumulation and toxicity may occur in patients with significant renal impairment or renal failure. Magnesium is dialyzable.
Pediatrics
Normal serum concentrations of magnesium range 1.5-2 mEq/L in children, and 1.5-2.3 mEq/L in neonates and infants.