Brand Name
(contains 64 mg of elemental magnesium per tablet, 100 mg of
elemental magnesium per enteric-coated tablet, 64 mg of elemental magnesium per
E.R. tablet, and 200 mg of elemental magnesium per 1 ml of injection)
Chloromag, Mag-L-100, Slow-Mag
magnesium citrate (citrate of magnesia)
(contains 40.5 to 47 mg elemental magnesium per 5 ml oral
solution)
Citroma, Citro-Mag (CAN)
magnesium gluconate
(contains 54 mg elemental magnesium per 5 ml oral solution and 27
to 29.3 mg elemental magnesium per tablet)
Almora, Maglucate (CAN), Magonate, Magtrate
magnesium hydroxide (milk of magnesia)
(contains 135 mg elemental magnesium per tablet, 129 to 130 mg
elemental magnesium per chewable tablet, and 164 to 328 mg elemental magnesium
per 5 ml liquid, liquid concentrate, or oral solution)
Phillips’ Chewable Tablets, Phillips’ Magnesia Tablets (CAN),
Phillips’ Milk of Magnesia, Phillips’ Milk of Magnesia Concentrate
magnesium lactate
(contains 84 mg elemental magnesium per E.R. tablet)
Mag-Tab SR Caplets
magnesium oxide
(contains 84.5 mg elemental magnesium per capsule and 50 to 302 mg
elemental magnesium per tablet)
Mag-200, Mag-Ox 400, Maox, Uro-Mag
magnesium sulfate
(contains 100 to 500 mg elemental magnesium per 1 ml of injection,
1 to 5 g elemental magnesium per 10 ml of injection, and 40 mEq per 5 mg of
crystals)
Class and Category
Chemical class: Cation, electrolyte
Therapeutic class: Antacid, antiarrhythmic, anticonvulsant,
electrolyte replacement, laxative
Pregnancy category: A (parenteral magnesium sulfate),
Not rated (others)
Indications and Dosages
To correct magnesium deficiency caused by alcoholism,
magnesium-depleting drugs, malnutrition, or restricted diet; to prevent
magnesium deficiency based on U.S. and Canadian recommended daily allowances
CAPSULES, CHEWABLE TABLETS, CRYSTALS, ENTERIC-COATED TABLETS, E.R.
TABLETS, LIQUID, LIQUID CONCENTRATE, ORAL SOLUTION, TABLETS (MAGNESIUM
CHLORIDE, CITRATE, GLUCONATE, HYDROXIDE, LACTATE [EXCEPT IN CHILDREN], OXIDE,
SULFATE)
Dosage individualized based on severity of deficiency and normal
recommended daily allowances listed below.
Adult men and children over age 10. 270 to 400
mg daily (Canada: 130 to 250 mg daily).
Adult women and children over age 10. 280 to 300
mg daily (Canada: 135 to 210 mg daily).
Pregnant women. 320 mg daily (Canada: 195
to 245 mg daily).
Breast-feeding women. 340 to 355 mg daily (Canada: 245
to 265 mg daily).
Children ages 7 to 10. 170 mg daily (Canada: 100
to 135 mg daily).
Children ages 4 to 6. 120 mg daily (Canada: 65
mg daily).
Children from birth to age 3. 40 to 80 mg/ day (Canada:
20 to 50 mg daily).
To treat mild
magnesium deficiency
I.M. INJECTION (MAGNESIUM SULFATE)
Adults and adolescents. 1 g every 6 hr for 4 doses.
To treat severe hypomagnesemia
I.V. INFUSION (MAGNESIUM CHLORIDE)
Adults. 4 g diluted in 250 ml D5W and infused at no more than 3 ml/min.
Maximum: 40 g daily.
I.V. INFUSION (MAGNESIUM SULFATE)
Adults and adolescents. 5 g diluted in 1 L I.V. solution
and infused over 3 hr.
To provide supplemental magnesium in total parenteral
nutrition
I.V. INFUSION (MAGNESIUM SULFATE)
Adults. 1 to 3 g daily.
Children. 0.25 mg to 1.25 g daily.
DOSAGE ADJUSTMENT Adult dosage may be increased to
6 g daily for certain conditions, such as short-bowel syndrome.
I.M. INJECTION (MAGNESIUM SULFATE)
Adults and adolescents. Up to 250 mg/kg every 4 hr,
p.r.n.
To prevent and control seizures in preeclampsia or
eclampsia as well as seizures caused by epilepsy, glomerulonephritis, or
hypothyroidism
I.V. INFUSION OR INJECTION (MAGNESIUM SULFATE)
Adults. Loading: 4 g diluted in 250 ml
compatible solution and infused over 30 min. Maintenance: 1 to 2 g/hr by
continuous infusion.
I.M. INJECTION (MAGNESIUM SULFATE)
Adults. 4 to 5 g every 4 hr, p.r.n.
Children. 20 to 40 mg/kg, repeated p.r.n.
To relieve indigestion with hyperacidity
CHEWABLE TABLETS, LIQUID, LIQUID CONCENTRATE, ORAL SOLUTION
TABLETS (MAGNESIUM HYDROXIDE)
Adults and adolescents. 400 to 1,200 mg (5 to 15 ml
liquid or 2.5 to 7.5 ml liquid concentrate) up to 4 times daily with water, or
622 to 1,244 mg (tablets or chewable tablets) up to 4 times daily.
CAPSULES, TABLETS (MAGNESIUM OXIDE)
Adults and adolescents. 140 mg (capsules) t.i.d. or
q.i.d. with water or milk, or 400 to 800 mg daily (tablets).
To relieve constipation, to evacuate colon for rectal or
bowel examination
LIQUID, LIQUID CONCENTRATE (MAGNESIUM HYDROXIDE)
Adults and children age 12 and over. 2.4 to 4.8
g (30 to 60 ml) daily as single dose or divided doses.
Children ages 6 to 11. 1.2 to 2.4 g (15 to 30 ml)/day as
a single dose or in divided doses.
Children ages 2 to 5. 0.4 to 1.2 g (5 to 15 ml) daily
as single dose or divided doses.
ORAL SOLUTION (MAGNESIUM CITRATE)
Adults and children age 12 and over. 11 to 25 g
daily as single dose or divided doses.
Children ages 6 to 11. 5.5 to 12.5 g daily as single
dose or divided doses.
Children ages 2 to 5. 2.7 to 6.25 g daily as single
dose or divided doses.
CRYSTALS (MAGNESIUM SULFATE)
Adults and children age 12 and over. 10 to 30 g
daily as single dose or divided doses.
DOSAGE ADJUSTMENT
Dosage limited to 20 g of magnesium sulfate every 48 hr for patients
with severe renal impairment.
Children ages 6 to 11. 5 to 10 g daily as a single dose
or in divided doses.
Children ages 2 to 5. 2.5 to 5 g daily as a single dose
or in divided doses.
CAPSULES, TABLETS (MAGNESIUM OXIDE)
Adults. 2 to 4 g with a full glass of water or milk, usually at bedtime.
Route Onset
Peak Duration
P.O.* 0.5–3
hr Unknown Unknown
P.O.† 20
min Unknown 20–180 min
I.M.‡ 1
hr Unknown 3–4 hr
I.V.‡ Immediate
Unknown About 30min
Mechanism of Action
Assists all enzymes involved in phosphate transfer reactions that
use adenosine triphosphate (ATP).Magnesium is required for normal function of
the ATP-dependent sodium-potassium pump in muscle membranes. It may effectively
treat digitalis glycoside– induced arrhythmias because correction of
hypomagnesemia improves the sodium-potassium pump’s ability to distribute potassium
into intracellular spaces and because magnesium decreases calcium uptake and
potassium outflow through myocardial cell membranes. As a laxative, magnesium
exerts a hyperosmotic effect in the small intestine. It causes water retention
that distends the bowel and causes the duodenum to secrete cholecystokinin. This
substance stimulates fluid secretion and
intestinal motility. As an antacid, magnesium
reacts with water, converting magnesium oxide
to magnesium hydroxide.Magnesium hydroxide rapidly reacts with gastric acid to form water and magnesium chloride, which increases gastric pH. As
an anticonvulsant, magnesium depresses the CNS
and blocks peripheral neuromuscular impulse
transmission by decreasing available acetylcholine.
Incompatibilities
Don’t
combine magnesium sulfate with alkali carbonates and bicarbonates, alkali hydroxides,
arsenates, calcium, clindamycin phosphate, dobutamine, fat emulsions, heavy
metals, hydrocortisone sodium succinate, phosphates, polymyxin B, procaine hydrochloride,
salicylates, sodium bicarbonate, strontium, and tartrates.
Contraindications
Hypersensitivity
to magnesium salts or any component of magnesium-containing preparations
For
magnesium chloride: Coma,
heart disease, renal impairment
For
magnesium sulfate: Heart
block, MI, preeclampsia 2 hours or less before delivery (I.V. form)
For
use as laxative: Acute
abdominal problem (as indicated by abdominal pain, nausea, or vomiting),
diverticulitis, fecal impaction, intestinal obstruction or perforation, colostomy
or ileostomy, severe renal impairment, ulcerative colitis
Interactions
DRUGS
amphotericin
B, cisplatin, cyclosporine, gentamicin: Possibly magnesium wasting and need
for magnesium dosage adjustment
anticholinergics:
Possibly
decreased absorption and therapeutic effects of these drugs
calcium
salts (I.V.): Possibly
neutralization of magnesium sulfate’s effects
cellulose
sodium phosphate: Possibly
binding with magnesium, possibly decreased therapeutic effectiveness of
cellulose
CNS
depressants: Increased
CNS depression
digoxin
(I.V.): Possibly
heart block and conduction changes, especially when calcium salts are also
administered
digoxin,
fluoroquinolones, folic acid, H2- receptor blockers, iron preparations,
isoniazid, ketoconazole, penicillamine, phenothiazines, phenytoin, phosphates
(oral), tetracyclines: Possibly decreased absorption and blood levels of
these drugs
diuretics
(loop or thiazide): Possibly
hypomagnesemia
edetate
sodium, sodium polystyrene sulfonate: Possibly binding with magnesium
enteric-coated
drugs: Possibly
quicker dissolution of these drugs and increased risk of adverse GI reactions
etidronate
(oral): Decreased
etidronate absorption
mecamylamine:
Possibly
prolonged effects of mecamylamine
methenamine,
streptomycin, sucralfate, tetracyclines, tobramycin (oral), urinary acidifiers:
Possibly
decreased therapeutic effects of these drugs
misoprostol:
Increased
misoprostol-induced diarrhea
neuromuscular
blockers: Possibly
increased neuromuscular blockade
nifedipine:
Possibly
increased hypotensive effects when taken with magnesium sulfate
potassium-sparing
diuretics: Increased
risk of hypermagnesemia
salicylates:
Possibly
increased excretion and lower blood levels of salicylates
sodium
polystyrene sulfonate resin: Possibly metabolic alkalosis
FOODS
high
glucose intake: Increased
urinary excretion of magnesium
ACTIVITIES
alcohol
use: Increased
urinary excretion of magnesium
Adverse
Reactions
CNS:
Confusion,
decreased reflexes, dizziness, syncope
CV:
Arrhythmias,
hypotension
GI:
Flatulence,
vomiting
MS:
Muscle
cramps
RESP:
Dyspnea,
respiratory depression or paralysis
SKIN:
Diaphoresis
Other:
Allergic
reaction, hypermagnesemia, injection site pain or irritation (I.M. form), laxative
dependence, magnesium toxicity
Nursing
Considerations
•
Be aware that magnesium sulfate is the elemental form
of magnesium. Oral preparations aren’t all equivalent.
• Be aware that drug isn’t metabolized. Drug remaining in the GI
tract produces watery stool within 30 minutes to 3 hours.
•Make sure patient chews chewable tablets thoroughly before
swallowing.
• Avoid giving other oral drugs within 2 hours of
magnesium-containing antacid.
• Before giving drug as laxative, shake oral solution, liquid, or
liquid concentrate well and give with a large amount of water.
WARNING Observe for and report early evidence of
hypermagnesemia: bradycardia, depressed deep tendon reflexes, diplopia, dyspnea,
flushing, hypotension, nausea, slurred speech, vomiting, and weakness.
WARNING Be aware that magnesium may precipitate
myasthenic crisis by decreasing patient’s sensitivity to acetylcholine.
• Frequently assess cardiac status of patient taking drugs that
lower heart rate, such as beta blockers, because magnesium may aggravate
symptoms of heart block.
WARNING Magnesium chloride for injection contains
the preservative benzyl alcohol, which may cause fatal toxic syndrome in neonates
and premature infants.
• Provide adequate diet, exercise, and fluids for patient being
treated for constipation.
•Monitor serum electrolyte levels in patients with renal
insufficiency because they’re at risk for magnesium toxicity.
• Be aware that magnesium salts aren’t intended for long-term use.
PATIENT TEACHING
• Advise patient to chew magnesium chewable tablets thoroughly
before swallowing then drink a full glass of water.Mention that tablets have a
chalky taste.
• Instruct patient to take magnesiumcontaining antacid between
meals and at bedtime. Urge him not to take other drugs within 2 hours of the
antacid.
• Tell patient to notify prescriber and avoid using
magnesium-containing laxative if he has abdominal pain, nausea, or vomiting.
• Instruct patient to refrigerate magnesium citrate solution.
• Caution patient about risk of dependence with long-term laxative
use.
• Teach patient to prevent constipation by increasing dietary
fiber and fluid intake and exercising regularly.
• Inform patient that magnesium supplements used to replace
electrolytes can cause diarrhea.
