Magnesium
Mg2+
What it isEssential cation with physiologic NMDA-channel blockade; deficiency, torsades de pointes, and eclamptic seizures.
Why this oneIt suppresses torsades even when serum magnesium is normal and is the standard anticonvulsant for eclampsia.
What limits itRenal accumulation causes loss of reflexes, respiratory depression, and heart block; monitor clinically and by level during sustained IV therapy.
Magnesium prescription history
Animated chart of estimated U.S. prescriptions per year, Constipation meds (1900–2026). Magnesium enters in 1900 (estimated).
Principal riskAccumulation in renal impairment; loss of reflexes
Classes and tags
Clinical profile
FDA label
Read the full label on DailyMed ↗
NO BOXED WARNINGS
| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Antacid — acid indigestion, upset stomach | Adults | 400 mg (1 tab) QD | 1-2 tabs (400-800 mg) QD | 2 tabs (800 mg)/24 h unless physician-directed |
Renal Ask a doctor before use in kidney disease (OTC label)
Hepatic Undefined
Instructions
- Do not exceed 2 tablets in 24 h unless directed by a physician
- May have a laxative effect
- Ask a doctor before use if taking any prescription drug (antacids may interact)
Available strengths
- tab 253, 400, 420, 440 mg
- tab 241.3 mg/1000 mg
Cautions
- Kidney disease — ask a doctor before use
- Antacids may interact with certain prescription drugs — ask a doctor or pharmacist
- May have a laxative effect
- Pregnant or breast-feeding — ask a doctor before use
Adverse reactions
- Laxative effect (OTC label lists no other adverse reactions)
Pregnancy OTC label: ask a doctor before use if pregnant.
Lactation OTC label: ask a doctor before use if breast-feeding.
Cost
| Strength | #/mo | generic $/mo | CostPlus | |
|---|---|---|---|---|
| 253 mg | tab | 30 qd | $1.15 | not offered |
| 400 mg | tab | 30 qd | $1.04 | not offered |
| 420 mg | tab | 30 qd | not offered | |
| 440 mg | tab | 30 qd | not offered | |
| 241.3 mg/1000 mg | tab | 30 qd | not offered |
Other forms: Magnesium oxide (MAG-OX)
Open Magnesium in the interactive console ↗
Self-check
- Can magnesium suppress torsades when serum magnesium is normal?
Yes. - What clinical sign can accompany magnesium accumulation?
Loss of reflexes.