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For information on the use of oral magnesium hydroxide, refer to the monograph for Antacids, Oral. Magnesium oxide and oral magnesium sulfate are also detailed in the monograph for Saline/Hyperosmotic laxatives in the GI section.
Chemistry – Magnesium sulfate occurs as small, usually needle-like, colorless crystals with a cool, saline, bitter taste. It is freely soluble in water and sparingly soluble in alcohol. Magnesium sulfate injection has a pH of 5.5-7. One gram of magnesium sulfate hexahydrate contains 8.1 mEq of magnesium. Magnesium sulfate is also known as Epsom salts.
Storage/Stability/Compatibility – Magnesium sulfate for injection should be stored at room temperature (15-30°C); avoid freezing. Refrigeration may result in precipitation or crystallization.
Magnesium sulfate is reportedly compatible with the following intravenous solutions and drugs: dextrose 5%, calcium gluconate, cephalothin sodium, chloramphenicol sodium succinate, cisplatin, hydrocortisone sodium succinate, isoproterenol HCl, methyldopate HCl, metoclopramide HCl (in syringes), norepinephrine bitartrate, penicillin G potassium, potassium phosphate, and verapamil HCl. Additionally, at Y-sites: acyclovir sodium, amikacin sulfate, ampicillin sodium, carbenicillin disodium, cefamandole naftate, cefazolin sodium, cefoperazone sodium, ceforanide, cefotaxime sodium, cefoxitin sodium, cephalothin sodium, cephapirin sodium, clindamycin phosphate, doxycycline phosphate, erythromycin lactobionate, esmolol HCl, gentamicin sulfate, heparin sodium, kanamycin sulfate, labetolol HCl, metronidazole (RTU), moxalactam disodium, nafcillin sodium, oxacillin sodium, piperacillin sodium, potassium chloride, tetracycline HCl, ticarcillin disodium, tobramycin sulfate, trimethoprim/sulfamethoxasole, vancomycin HCl, and vitamin B-complex with C.
Magnesium sulfate is reportedly incompatible with alkali hydroxides, alkali carbonates, salicylates and many metals, including the following solutions or drugs: fat emulsion 10 %, calcium gluceptate, dobutamine HCl, polymyxin B sulfate, procaine HCl, and sodium bicarbonate. Compatibility is dependent upon factors such as pH, concentration, temperature and diluents used. It is suggested to consult specialized references for more specific information (e.g., Handbook on Injectable Drugs by Trissel; see bibliography).
Pharmacology – Magnesium is used as a cofactor in a variety of enzyme systems and plays a role in muscular excitement and neurochemical transmission.
Uses/Indications – Parenteral magnesium sulfate is used as a source of magnesium in magnesium deficient states (hypomagnesemia), for adjunctive therapy of malignant hyperthermia in swine, and also as an anticonvulsant.
Pharmacokinetics – IV magnesium results in immediate effects, IM administration may require about 1 hour for effect. Magnesium is about 30-35% bound to proteins and the remainder exists as free ions. It is excreted by the kidneys at a rate proportional to the serum concentration and glomerular filtration.
Contraindications/Precautions – Parenteral magnesium is contraindicated in patients with myocardial damage or heart block. Magnesium should be given with caution to patients with impaired renal function. Patients receiving parenteral magnesium should be observed and monitored carefully to avoid hypermagnesemia.
Adverse Effects/Warnings – Magnesium sulfate (parenteral) adverse effects are generally the result of magnesium overdosage and may include drowsiness or other CNS depressant effects, muscular weakness, bradycardia, hypotension, respiratory depression and increased Q-T intervals on ECG. Very high magnesium levels may cause neuromuscular blocking activity and eventually cardiac arrest.
Overdosage/Acute Toxicity – See Adverse Effects above. Treatment of hypermagnesemia is dependent on the serum magnesium level and any associated clinical effects. Ventilatory support and administration of intravenous calcium may be required for severe hypermagnesemia.
Drug Interactions – When parenteral magnesium sulfate is used with other CNS depressant agents (e.g., barbiturates, general anesthetics) additive CNS depression may occur.
Parenteral magnesium sulfate with nondepolarizing neuromuscular blocking agents has caused excessive neuromuscular blockade. Because serious conduction disturbances can occur, parenteral magnesium should be used with extreme caution with digitalis cardioglycosides. Concurrent use of calcium salts may negate the effects of parenteral magnesium.
For hypomagnesemia (grass and other magnesium-related tetanies):
a) Cattle: Magnesium sulfate 20-50%: 200 ml SQ, followed by a slow IV infusion of 500 ml of a calcium/magnesium solution (Calcium borogluconate 23%; MgCl2 6%). (Phillips 1988a)
b) Cattle: 350 ml (250 ml of 25% calcium borogluconate and 100 ml of 10% of magnesium sulfate) by slow IV. If not a proprietary mixture, give calcium first. Relapses occur frequently after IV therapy, and 350 ml SQ of magnesium sulfate 20% may give more sustained magnesium levels. Alternating calcium and magnesium may prevent adverse effects. Continue control measures for 4-7 days to prevent relapse.
Sheep and Goats: 50 – 100 ml of above solution (calcium/magnesium).
For whole milk tetany in calves 2-4 months of age: Magnesium sulfate 10% 100 ml; followed by oral magnesium oxide at daily doses of 1 gram PO (0-5 weeks old), 2 gram PO (5-10 weeks old), and 3 grams PO (10-15 weeks old). (Merrall and West 1986)
Monitoring Parameters –
1) Serum magnesium
2) Physical signs and symptoms associated with hypomagnesemia
3) Serum calcium if indicated
Dosage Forms/Preparations/FDA Approval Status/Withholding Times –
Veterinary-Approved Products: There are no parenteral magnesium-only products approved for veterinary medicine. There are, however, several proprietary magnesium-containing products available that may also include calcium, phosphorus, potassium and/or dextrose; refer to the individual product’s labeling for specific dosage information. Trade names for these products include: Norcalciphos® —Pfizer, Cal-Dextro® Special, & #2,—Fort Dodge, and CMPK ®, & Cal-Phos® #2 —(TechAmerica). They are legend (Rx) drugs.
Magnesium Sulfate Injection 10% (0.8 mEq/ml), 12.5% (1 mEq/ml), & 50%
(4mEq/ml) in 2, 5, 10, 20 & 50 ml amps, vials and/or syringes; Generic; (Rx)