Hypomagnesemia
at the bedside
- check vitals · confirm Mg < 0.7 mmol/L (1.7 mg/dL)
- look for → tremors, tetany, seizures
- identify + treat cause
- GI loss, alcohol, diuretics, PPIs
low Mg blocks correction of K and Ca
- drives refractory hypokalemia + hypocalcemia: replace Mg first
escalate now if
- unstable or ECG changes → call for help
- torsades de pointes or hemodynamic instability from low Mg
focused check
| category | common causes |
|---|---|
| GI losses | diarrhea, malabsorption, pancreatitis, PPIs |
| urinary losses | diuretics, aminoglycosides, amphotericin, cisplatin, calcineurin inhibitors |
| metabolic | alcohol use, uncontrolled diabetes, hypercalcemia |
| renal / tubular | post-ATN recovery, post-obstructive diuresis |
| genetic (rare) | Bartter, Gitelman, familial hypomagnesemia |
send now
- check K⁺ + Ca²⁺ alongside
- ECG if unstable or symptomatic
treat
by level & symptoms, IV MgSO₄
| 0.5–0.7mild · asymptomatic · mmol/L | oral Mg: citrate, chloride, or lactate preferred (oxide poorly absorbed) · 12–24 mmol/day in divided doses · diarrhea is dose-limiting · continue 2 days after normalizing |
| 0.5–0.7moderate · symptomatic or IV needed · mmol/L | 2–4 g IV over 4–12 h |
| < 0.5or symptomatic | 1–2 g IV over 1 h · repeat every 6–12 h if needed |
| < 0.3very low / ongoing losses · mmol/L | 4–6 g IV over 12–24 h |
emergencies, push faster, get help
- hemodynamic instability → 1–2 g IV over 2–15 min · repeat, then slow infusion
- torsades de pointes → 1–2 g IV over ~15 min · up to 4 g total · then 0.5–1 g/h
- replace slowly: up to 50% lost in urine if infused too fast
- in CKD, reduce dose ~25–50%, monitor closely; in AKI or severe CKD, get specialist input before replacing
available magnesium
| product | content | usual adult dose | bedside note |
|---|---|---|---|
| IV magnesium sulfate 50% | 2 mmol/mL: 10 mL ampoule = 5 g = 20 mmol Mg (1 g = 4 mmol) | replacement as in treat above: 1–2 g (4–8 mmol) IV over 1 h, repeat 6–12 h; repletion 32–48 mmol (8–12 g) in the first 24 h, then 16–24 mmol/day for 3–4 days | dilute to ≤ 20% (e.g. 2 g in ≥ 50 mL NaCl 0.9% or glucose 5%); max 8 mmol/h (2 g/h) outside emergencies; renal impairment: 25–50% of the dose, monitor levels |
| oral magnesium salts | citrate, chloride or lactate preferred; oxide poorly absorbed | 12–24 mmol/day in divided doses (treat table) | diarrhea is dose-limiting; mmol per tablet varies by product: local formulation verification needed |
recheck
- recheck Mg 6–12 h after IV dose
- repeat based on levels + symptoms
before leaving
- document: Mg value + trend, replacement given, K/Ca checked
- pending: repeat Mg, K, Ca
- hand over: last Mg + time, next recheck, escalation trigger if refractory
hypermagnesemia
causes
- usually renal failure or iatrogenic (Mg therapy, Mg-containing antacids/laxatives)
features
- hyporeflexia, weakness, hypotension, bradycardia
- severe → respiratory depression, arrest
management
- stop all magnesium sources
- calcium gluconate 1 g IV: antagonizes cardiac/neuromuscular effects
- IV fluids ± loop diuretic if renal function adequate
- dialysis if severe or in renal failure
evidence
| source | type |
|---|---|
| Standard electrolyte-replacement practice, renal dose-adjustment | common practice |
Verify indication, dose, allergies, interactions, renal/hepatic function and local protocols before prescribing.
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reviewed Jun 2026updated Sep 2026file lab/rft-magnesium