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Pharmacologic class: Mineral
Therapeutic class: Electrolyte replacement, laxative, antacid, anticonvulsant
Pregnancy risk category A (magnesium sulfate), NR (magnesium citrate, hydroxide, oxide), unknown (magnesium chloride, gluconate)
Increases osmotic gradient in small intestine, which draws water into intestines and causes distention. These effects stimulate peristalsis and bowel evacuation. In antacid action, reacts with hydrochloric acid in stomach to form water and increase gastric pH. In anticonvulsant action, depresses CNS and blocks transmission of peripheral neuromuscular impulses.
Oral solution: 240-ml, 296-ml, and 300-ml bottles
Liquid: 1,000 mg/5 ml
Tablets: 500 mg
Liquid: 400 mg/5 ml
Liquid concentrate: 800 mg/5 ml
Tablets (chewable): 300 mg
Capsules: 140 mg
Tablets: 250 mg, 400 mg, 420 mg, 500 mg
Granules (for oral use): 120 g, 4 lb
Injection: 10%, 12.5%, 25%, 50%
Indications and dosages
➣ Mild magnesium deficiency
Adults: 1 g (2 ml of 50% sulfate solution) I.M. q 6 hours for four doses
➣ Severe hypomagnesemia
Adults: 250 mg (2 mEq)/kg (sulfate) I.M. within 4-hour period, or 5 g (approximately 40 mEq) in 1 liter 5% dextrose injection or 0.9% sodium chloride solution by I.V. infusion over 3 hours
➣ Hypomagnesemia treatment
Adults and children: Dosage individualized based on severity of deficiency; may give citrate, gluconate, hydroxide, oxide, or sulfate.
➣ Hypomagnesemia prophylaxis
Adults and children: Dosage based on normal recommended daily magnesium intake; may give citrate, gluconate, hydroxide, oxide, or sulfate.
➣ Supplemental magnesium in total parenteral nutrition (TPN)
Adults: 8 to 24 mEq/day (sulfate) by I.V. infusion, added to TPN solution
Adults and children ages 12 and older: 15 g (sulfate granules) in 240 ml water; or 30 to 60 ml/day P.O. (hydroxide) given with water; or a single dose of 10 to 30 ml P.O. (hydroxide concentrate); or one bottle of oral solution (citrate), as directed
Children ages 6 to 11: 5 to 10 g (sulfate granules) in 120 ml water; or a single dose of 2.5 to 5 ml P.O. (sulfate) in a half-glass of water; or 15 to 30 ml P.O. daily (hydroxide) given with water; or a single dose of 7.5 to 15 ml P.O. (hydroxide concentrate); or three to four tablets (hydroxide); or 50 to 100 ml, as directed, of oral solution (citrate)
Children ages 2 to 5: Single dose of 5 to 15 ml P.O. (hydroxide); or 2.5 to 7.5 ml P.O. daily (hydroxide concentrate); or one to two tablets (hydroxide); or 4 to 12 ml oral solution (citrate), as directed
Adults and children ages 12 and older: 5 to 15 ml P.O. (hydroxide liquid) up to q.i.d. with water; or 2.5 to 7.5 ml P.O. (hydroxide liquid concentrate) up to q.i.d. with water; or 622 to 1,244 mg P.O. (hydroxide tablets) up to q.i.d.; or 400 to 800 mg P.O. (oxide tablets) daily
➣ To prevent and control seizures in preeclampsia or eclampsia
Adults: 4 to 5 g 50% sulfate solution I.M. q 4 hours, as necessary; or 4 g 10% to 20% sulfate solution I.V., not to exceed 1.5 ml/minute of 10% solution; or 4 to 5 g I.V. infusion in 250 ml of 5% dextrose or sodium chloride solution, not to exceed 3 ml/minute
➣ Acute nephritis to control hypertension, encephalopathy, and seizures in children
Children: 100 mg/kg 50% sulfate solution I.M. q 4 to 6 hours as needed; or 20 to 40 mg/kg 20% solution I.M., repeated as necessary
• Bronchodilation in some asthmatic patients
• Post-myocardial infarction hypomagnesemia
• Heart block
• Myocardial damage
• Active labor or within 2 hours of delivery
Use cautiously in:
• renal insufficiency, abdominal pain, nausea and vomiting, rectal bleeding, anuria, hypocalcemia
• pregnant patients.
☞ Be aware that magnesium sulfate injection is a high-alert drug.
• Know that I.V. use is reserved for life-threatening seizures.
• When giving magnesium sulfate I.V., don't exceed concentration of 20% or infusion rate of 150 mg/minute, except in seizures caused by severe eclampsia. Too-rapid I.V. infusion may cause hypotension and asystole.
• When giving magnesium sulfate I.M. to adults, use concentration of 25% to 50%; when giving to infants and children, don't exceed 20%.
CNS (with I.V. use): confusion, decreased reflexes, dizziness, syncope, sedation, hypothermia, paralysis
CV (with I.V. use): hypotension, arrhythmias, circulatory collapse
GI: nausea, vomiting, cramps, flatulence, anorexia
Metabolic: hypermagnesemia, hypocalcemia
Musculoskeletal (with I.V. use): muscle weakness, flaccidity
Respiratory: respiratory paralysis Skin: diaphoresis
Other: allergic reaction, injection site reaction, laxative dependence (with repeated or prolonged use)
Drug-drug. Aminoquinolones, nitrofurantoin, penicillamine, tetracyclines: decreased absorption of these drugs (with oral magnesium)
CNS depressants: additive effects
Digoxin: heart block, conduction changes (with I.V. use)
Enteric-coated drugs: faster dissolution of these drugs
Neuromuscular blockers: increased effects of these drugs (with I.V. use)
Drug-diagnostic tests. Calcium, magnesium: increased levels (with I.V. use)
☞ When giving prolonged or repeated I.V. infusions, assess patellar reflex and monitor for respiratory rate of 16 breaths/minute or more.
☞ With I.V. use, monitor blood magnesium level (desired level is 3 to 6 mg/dl or 2.5 to 5 mEq/L). Check for signs and symptoms of magnesium toxicity (hypotension, nausea, vomiting, ECG changes, muscle weakness, mental or respiratory depression, coma). Keep injectable calcium on hand to counteract magnesium toxicity.
• Monitor urine output, which should measure 100 ml or more every 4 hours.
☞ If I.V. magnesium was given before delivery, assess neonate for signs and symptoms of magnesium toxicity, such as neuromuscular or respiratory depression.
• Monitor electrolyte levels and liver function tests.
☞ Teach patient about adverse reactions. Instruct him to report symptoms that occur during I.V. administration.
• Advise patient to consult prescriber before using magnesium if he's taking other drugs. Magnesium may delay or enhance absorption of other drugs.
• Inform patient that repeated or prolonged use of magnesium citrate, hydroxide, or sulfate may cause laxative dependence. Inform him that healthy diet and exercise can reduce need for laxatives.
• Tell pregnant female to make sure prescriber knows she is pregnant before taking drug.
• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs and tests mentioned above.