Effects of intravenous magnesium sulfate on serum calcium-regulating hormones and plasma and urinary electrolytes in healthy horses.
Authors: Schumacher Stephen A, Kamr Ahmed M, Lakritz Jeffrey, Burns Teresa A, Bertone Alicia L, Toribio Ramiro E
Journal: PloS one
Summary
# Editorial Summary: Magnesium Sulphate and Calcium Regulation in Horses When veterinarians and event organisers administer intravenous magnesium sulphate—whether to treat hypomagnesaemia, cardiac dysrhythmias, or as a sedative—the resulting spike in blood magnesium triggers a cascade of hormonal and electrolytic changes that until now remained poorly characterised in equine medicine. Schumacher and colleagues studied twelve healthy mares (aged 4–18 years, 432–600 kg) receiving a single 60 mg/kg IV bolus of MgSO₄, collecting blood and urine samples over six hours to measure parathyroid hormone, calcitonin, ionised calcium, and major electrolytes. Plasma magnesium increased 3.7-fold within five minutes and stayed elevated for two hours; critically, ionised calcium dropped significantly between 30–60 minutes post-administration, whilst parathyroid hormone initially suppressed before rebounding and remaining elevated during the same window—an apparent compensatory mechanism. Fractional urinary excretion of magnesium, calcium, sodium, potassium and chloride all increased substantially, with urine osmolality falling concurrently, indicating that the kidneys actively shed both the excess magnesium and secondary electrolytic losses. These findings warrant careful consideration in clinical practice: whilst short-term magnesium administration is generally safe in healthy horses, practitioners should monitor calcium-regulating hormones and electrolytes in patients receiving repeated doses or those with pre-existing renal compromise, particularly given the increased urinary losses of essential minerals and the transient hypocalcaemia observed.
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Practical Takeaways
- •When using MgSO4 as a calming agent or therapeutic, be aware it causes temporary hypocalcemia (30-60 min window) and increases urinary electrolyte losses—monitor hydration status and consider fluid support in dehydrated or compromised horses
- •The short-term effects of MgSO4 on calcium regulation and PTH/calcitonin suggest careful consideration when treating horses with concurrent calcium dysregulation or neuromuscular conditions
- •MgSO4's effects are transient; most electrolyte and hormonal changes resolve within 2 hours, but increased urine output suggests adequate water and electrolyte intake is important post-treatment
Key Findings
- •Intravenous MgSO4 (60 mg/kg) increased plasma magnesium 3.7-fold at 5 minutes, remaining elevated for 120 minutes
- •Calcium concentrations decreased 30-60 minutes post-administration despite initial PTH and calcitonin responses
- •Magnesium sulfate significantly increased urinary fractional excretion of magnesium, calcium, sodium, potassium, and chloride within 30-60 minutes
- •Hypermagnesemia triggered biphasic PTH response (initial drop followed by elevation 30-60 minutes) and transient calcitonin elevation