Magnesium Salts

Electrolyte replacement, Antacid (hydroxide), Osmotic laxative (citrate, hydroxide), Antiarrhythmic (IV sulfate, torsades)

Magnesium (oxide, citrate, sulfate, hydroxide, gluconate, chloride salts)

Mag-Ox, Slow-Mag, MagCitrate, Milk of Magnesia (hydroxide); IV sulfate generic

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Pharmacy

Starting dose

Replacement oxide 400-800 mg/d in divided doses (high diarrhea rate); citrate 200-400 mg/d (better tolerated, better absorbed); IV sulfate 1-2 g over 5-60 minutes for hypomagnesemia or torsades; eclampsia 4-6 g IV loading then 1-2 g/h

Preparations

Oxide 400, 500 mg tablets (240, 300 mg elemental); citrate 100, 150, 200 mg tablets; hydroxide oral suspension 400 mg/5 mL; sulfate IV 500 mg/mL ampules

US FDA Max

Indication-specific; renal clearance limits tolerable cumulative dosing

Common uses

Classification(s)

Classes

Electrolyte replacement, Antacid (hydroxide), Osmotic laxative (citrate, hydroxide), Antiarrhythmic (IV sulfate, torsades)

Pharmacology

Routes

Oral, IV

Onset

Oral: hours; IV: minutes

Duration

Variable

Half-life

Not meaningfully described (electrolyte; renally cleared)

Bioavailability

Highly salt-dependent: citrate ~25-30%; oxide ~4% (limited and causes osmotic diarrhea); chloride ~12%

Pregnancy

IV sulfate is the cornerstone of eclampsia/preeclampsia management; oral replacement also safe.^{[citation needed]}

Legal status

OTC (oral salts) and Rx-only (IV) in US

Purported mechanism

Magnesium is essential for ~300 enzyme reactions including ATP-dependent processes (ATP-Mg complex is the bioactive form), competes with calcium at L-type voltage-gated channels (membrane stabilization, the basis of IV use in torsades and eclampsia seizure prevention), and modulates NMDA glutamate receptor activity.▲0▼ Renally cleared; accumulation in advanced CKD can produce neuromuscular and cardiac depression. Hypomagnesemia frequently co-exists with hypokalemia and is often the reason refractory potassium loss does not correct until magnesium is repleted.

Pharmacopedia is intended for reference. Nothing here is advice. In an emergency call 911; US Poison Control 1-800-222-1222. See the full disclaimer.