MAGNESIUM SULFATE

MAGNESIUM SULFATE
(mag-nes'i-um)
Epsom Salt
Classifications: saline cathartic; replacement agent; anticonvulsant;
Therapeutic: laxative
; electrolyte replacement; anticonvulsant
Prototype: Magnesium hydroxide
Pregnancy Category: A

Availability

0.8 mEq/mL, 1 mEq/mL, 4 mEq/mL injection

Action

Orally: Acts as a laxative by osmotic retention of fluid, which distends colon, increases water content of feces, and causes mechanical stimulation of bowel activity. Parenterally: Acts as a CNS depressant and also as a depressant of smooth, skeletal, and cardiac muscle function. Anticonvulsant properties thought to be produced by CNS depression, principally by decreasing the amount of acetylcholine liberated from motor nerve terminals, thus producing peripheral neuromuscular blockade.

Therapeutic Effect

Effective parenterally as a CNS depressant, smooth muscle relaxant and anticonvulsant in labor and delivery, and cardiac disorders. It is a laxative when taken orally.

Uses

Orally to relieve acute constipation and to evacuate bowel in preparation for x-ray of intestines. Parenterally to control seizures in toxemia of pregnancy, epilepsy, and acute nephritis and for prophylaxis and treatment of hypomagnesemia. Topically to reduce edema, inflammation, and itching.

Unlabeled Uses

To inhibit premature labor (tocolytic action) and as adjunct in hyperalimentation, to alleviate bronchospasm of acute asthma, to reduce mortality post-MI.

Contraindications

Myocardial damage; AV heart block; cardiac arrest except for certain arrhythmias; hypermagnesemia; GI obstruction; IV administration during the 2 h preceding delivery; PO use in patients with abdominal pain, nausea, vomiting, fecal impaction, or intestinal irritation, obstruction, or perforation.

Cautious Use

Renal disease; renal failture; renal impairment; acute MI; digitalized patients; concomitant use of other CNS depressants; neuromuscular blocking agents, or cardiac glycosides; children.

Route & Dosage

Laxative
Adult: PO 10–15 g once/d

Seizures
Adult: IV 1 g, may need to repeat dose

Preeclampsia, Eclampsia
Adult: IM/IV 4–5 g in 250 mL D5W infused slowly; simultaneously, 5 g IM in alternate buttocks q4h

Hypomagnesemia
Adult: IM/IV Mild, 1 g q6h for 4 doses; Severe, 5 g infused over 3 h
Child: IV 25–50 mg/kg q4–6h prn (max single dose: 2000 mg)

Total Parenteral Nutrition
Adult: IV 0.5–3 g/d

Administration

Oral
  • Give in the morning or mid-afternoon in a glass of water for laxative action. Disguise bitter, salty taste by chilling or flavoring with lemon or orange juice.
Intramuscular
  • Give deep using the 50% concentration for adults and the 20% concentration for children.
Intravenous
  • Note: Verify correct IV concentration and rate of infusion for administration to infants, children with physician.

PREPARE: Direct/IV Infusion: ??Give solutions with concentrations of ≤20% undiluted. ??Dilute more concentrated solutions to 20% (200 mg/mL) or less with D5W or NS. 

ADMINISTER: Direct: Give at a rate of 150 mg over at least 1 min. Note: 20% solution contains 200 mg/mL, 10% solution contains 100 mg/mL.  IV Infusion: Give required dose over 4 h. Do not exceed the direct rate.  

INCOMPATIBILITIES Solution/additive: 10% fat emulsion, amphotericin B, calcium, chlorpromazine, clindamycin, cyclosporine, dobutamine, hydralazine, polymyxin B sulfate, potassium, procaine, prochlorperazine, sodium bicarbonate. Y-site: Amiodarone, amphotericin B, cholesteryl, cefepime, ciprofloxacin, haloperidol.

Adverse Effects (≥1%)

Body as a Whole: Flushing, sweating, extreme thirst, sedation, confusion, depressed reflexes or no reflexes, muscle weakness, flaccid paralysis, hypothermia. CV: Hypotension, depressed cardiac function, complete heart block, circulatory collapse. Respiratory: Respiratory paralysis. Metabolic: Hypermagnesemia, hypocalcemia, dehydration, electrolyte imbalance including hypocalcemia with repeated laxative use.

Interactions

Drug: neuromuscular blocking agents add to respiratory depression and apnea.

Pharmacokinetics

Onset: 1–2 h PO; 1 h IM. Duration: 30 min IV; 3–4 h PO. Distribution: Crosses placenta; distributed into breast milk. Elimination: In kidneys.

Nursing Implications

Assessment & Drug Effects

  • Observe constantly when given IV. Check BP and pulse q10–15min or more often if indicated.
  • Lab tests: Monitor plasma magnesium levels in patients receiving drug parenterally (normal: 1.8–3.0 mEq/L). Plasma levels in excess of 4 mEq/L are reflected in depressed deep tendon reflexes and other symptoms of magnesium intoxication (see ADVERSE EFFECTS). Cardiac arrest occurs at levels in excess of 25 mEq/L. Monitor calcium and phosphorus levels also.
  • Early indicators of magnesium toxicity (hypermagnesemia) include cathartic effect, profound thirst, feeling of warmth, sedation, confusion, depressed deep tendon reflexes, and muscle weakness.
  • Monitor respiratory rate closely. Report immediately if rate falls below 12.
  • Test patellar reflex before each repeated parenteral dose. Depression or absence of reflexes is a useful index of early magnesium intoxication.
  • Check urinary output, especially in patients with impaired kidney function. Therapy is generally not continued if urinary output is less than 100 mL during the 4 h preceding each dose.
  • Observe newborns of mothers who received parenteral magnesium sulfate within a few hours of delivery for signs of toxicity, including respiratory and neuromuscular depression.
  • Observe patients receiving drug for hypomagnesemia for improvement in these signs of deficiency: Irritability, choreiform movements, tremors, tetany, twitching, muscle cramps, tachycardia, hypertension, psychotic behavior.
  • Have calcium gluconate readily available in case of magnesium sulfate toxicity.

Patient & Family Education

  • Drink sufficient water during the day when drug is administered orally to prevent net loss of body water.
  • Recommended daily allowances of magnesium are obtained in a normal diet. Rich sources are whole-grain cereals, legumes, nuts, meats, seafood, milk, most green leafy vegetables, and bananas.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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