indication

Used for immediate control of life-threatening convulsions in the treatment of severe toxemias (pre-eclampsia and eclampsia) of pregnancy and in the treatment of acute nephritis in children. Also indicated for replacement therapy in magnesium deficiency, especially in acute hypomagnesemia accompanied by signs of tetany similar to those of hypocalcemia. Also used in uterine tetany as a myometriat relaxant.

pharmacology

Magnesium sulfate is a small colorless crystal used as an anticonvulsant, a cathartic, and an electrolyte replenisher in the treatment of pre-eclampsia and eclampsia. It causes direct inhibition of action potentials in myometrial muscle cells. Excitation and contraction are uncoupled, which decreases the frequency and force of contractions. Magnesium sulfate is gaining popularity as an initial treatment in the management of various dysrhythmias, particularly torsades de pointes, and dyrhythmias secondary to TCA overdose or digitalis toxicity.

mechanism of action

Magnesium is the second most plentiful cation of the intracellular fluids. It is essential for the activity of many enzyme systems and plays an important role with regard to neurochemical transmission and muscular excitability. Magnesium sulfate reduces striated muscle contractions and blocks peripheral neuromuscular transmission by reducing acetylcholine release at the myoneural junction. Additionally, Magnesium inhibits Ca²⁺ influx through dihydropyridine-sensitive, voltage-dependent channels. This accounts for much of its relaxant action on vascular smooth muscle.

toxicity

LD₅₀ = 1200 mg/kg (rat, subcutaneous). May be harmful if swallowed. May act as an irritant. Adverse reactions include hypotension, ECG changes, diarrhea, urinary retention, CNS depression and respiratory depression.

biotransformation

None

half life

43.2 hours (for newborns)

route of elimination

Magnesium is excreted solely by the kidney at a rate proportional to the serum concentration and glomerular filtration.

drug interactions

Atazanavir: This gastric pH modifier decreases the levels/effects of atazanavir

Tiludronate: The divalent cation of oral Magnesium sulfate may significantly decrease the absorption of Tiludronate by forming a nonabsorbable chelate. Oral dosing should be separated by at least 2 hours.

Triprolidine: The CNS depressants, Triprolidine and Magnesium sulfate, may increase adverse/toxic effects due to additivity. Monitor for increased CNS depressant effects during concomitant therapy.

Trovafloxacin: Magnesium may decrease the absorption of orally administered Trovafloxacin. Administer Trovafloxacin 2 hours before or 6 hours after a dose of the magnesium containing agent to minimize the interaction.