Can magnesium glycinate 120 mg cause facial flushing or a hot face in a patient with sick‑sinus‑syndrome‑associated bradycardia?

Magnesium Glycinate and Facial Flushing

Magnesium glycinate at 120 mg is unlikely to cause facial flushing or a hot face, as this symptom is not a recognized adverse effect of oral magnesium supplementation at therapeutic doses, and the dose in question is well below levels associated with any magnesium toxicity.

Understanding Magnesium-Related Flushing

The evidence does not support magnesium glycinate as a cause of facial flushing:

• Magnesium toxicity symptoms begin at much higher serum levels (>2.5 mmol/L), manifesting initially as loss of reflexes, muscle weakness, and sedation, not flushing 1
• Facial flushing is not listed among the adverse effects of magnesium supplementation in any of the comprehensive guideline reviews of magnesium therapy 1, 2
• The 120 mg dose of magnesium glycinate is well within the safe therapeutic range for oral supplementation, which typically ranges from 12-24 mmol daily (approximately 288-576 mg elemental magnesium) 2

Differential Diagnosis: Alternative Causes of Facial Flushing

Several medications and conditions commonly cause flushing that should be considered instead:

• Calcium channel blockers (nifedipine, nicardipine, verapamil) cause headache, flushing, and reflex tachycardia as common adverse effects 3
• Hydralazine causes headache, palpitations, tachycardia, nausea/vomiting, and flushing 3
• Niacin, nicotine, catecholamines, angiotensin-converting enzyme inhibitors, and alcohol can all induce flushing episodes 3
• Vasodepressor (vasovagal) reactions can present with pallor, weakness, nausea, vomiting, and diaphoresis, though typically with bradycardia rather than a sensation of facial warmth 3

Special Considerations in Sick Sinus Syndrome

In patients with sick sinus syndrome and bradycardia, the clinical context is important:

• Sick sinus syndrome results from intrinsic sinoatrial node dysfunction or extrinsic reversible causes, with symptoms related to end-organ hypoperfusion 4, 5
• Magnesium supplementation does not adversely affect sinus node function at therapeutic doses and is not contraindicated in bradycardia 3
• Beta-agonists used to treat bradycardia (isoproterenol, dopamine, epinephrine) can cause flushing as a side effect, but magnesium does not share this property 3

Magnesium Toxicity: When Symptoms Actually Occur

To provide context on when magnesium truly causes problems:

• Mild toxicity (2.5-5 mmol/L): loss of reflexes, muscle weakness, sedation 1
• Moderate toxicity (4-5 mmol/L): severe muscular weakness, respiratory depression 1
• Severe toxicity (6-10 mmol/L): complete paralysis, cardiac arrest, cardiovascular collapse 1
• Rapid IV infusion of magnesium sulfate can cause hypotension and bradycardia, but oral magnesium glycinate does not produce these effects 2

Clinical Recommendation

The facial flushing is almost certainly unrelated to the magnesium glycinate 120 mg. A thorough medication review should focus on calcium channel blockers, vasodilators, niacin, or other known flushing-inducing agents 3. Consider evaluating for postmenopausal flush, carcinoid syndrome, pheochromocytoma, or other endocrine causes if no medication culprit is identified 3.

In patients with sick sinus syndrome, magnesium supplementation at this dose poses no additional risk and may actually be beneficial if there is concurrent hypomagnesemia, which can predispose to arrhythmias 2.