# Magnesium: The Link to Potassium, Calcium, and Rhythm

Low magnesium can make potassium and calcium treatment fail; high magnesium can suppress reflexes, respiration, and cardiac conduction.

![Infographic: Magnesium: The Link to Potassium, Calcium, and Rhythm](https://urinenephrology.org/visual-reference/images/magnesium-disorders.png?v=20261003c)

## Low magnesium: look for linked abnormalities

Tremor, cramps, seizures, QT-related arrhythmias, refractory hypokalemia, or hypocalcemia should prompt magnesium measurement. Serum magnesium samples only a small fraction of body stores, so a normal result does not fully exclude depletion in a compelling clinical setting.

## Find GI versus renal loss

Review diarrhea, poor intake, alcohol use, PPIs, loop/thiazide diuretics, aminoglycosides, and platinum therapy. Persistent unexplained deficiency may need urinary magnesium assessment before replacement when feasible. Interpret renal wasting indices cautiously with CKD and current supplementation.

## Match replacement to urgency

Oral replacement suits stable patients with a functioning gut, but diarrhea may limit it. Severe symptoms, arrhythmia, or poor absorption can require monitored IV magnesium. Torsades management is an emergency protocol even when a serum magnesium result is not low.

## Correct partners concurrently

Magnesium deficiency increases renal potassium loss and impairs PTH function. Replace deficient magnesium alongside potassium/calcium care; do not postpone urgent treatment of a dangerous potassium or calcium abnormality. Repeat levels because serum improvement may precede restoration of stores.

## High magnesium: check exposures and excretion

In AKI or advanced CKD, magnesium-containing laxatives, antacids, or infusions can accumulate. Weakness, reduced reflexes, hypotension, bradycardia, or respiratory depression requires urgent assessment. Stop the source and support airway, ventilation, and circulation.

## Antagonize, then eliminate

IV calcium can temporarily oppose serious magnesium toxicity; it does not remove magnesium. Severe toxicity with poor kidney clearance may need dialysis. Fluid/diuretic-assisted excretion is only suitable when kidney function and volume tolerance permit, not a default forced-diuresis order.

## Supporting evidence

- [Clinical evidence and guidance](https://pmc.ncbi.nlm.nih.gov/articles/PMC5314808/)
- [PubMed 25540137](https://pubmed.ncbi.nlm.nih.gov/25540137/)

## Source lessons

- [hypermagnesemia](https://urinenephrology.org/2025_UDPA_Lectures_Live/electrolytes/magnesium/hypermagnesemia.html)
- [hypomagnesemia](https://urinenephrology.org/2025_UDPA_Lectures_Live/electrolytes/magnesium/hypomagnesemia.html)
- [index](https://urinenephrology.org/2025_UDPA_Lectures_Live/electrolytes/magnesium/index.html)

Read alongside the full lessons; the findings and decisions shown here require the stated clinical context.