Magnesium Sulfate
Magnesium sulfate
Also known as: Epsom Salts · Magnesium sulphate injection BP · MgSO4
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Dosing by species
Dosing data for this drug is not yet available in the VetSheet formulary. Every other section below is complete. Consult the current product label before prescribing.
Overview
Magnesium sulfate, commonly known as Epsom salt, is a versatile compound used in veterinary medicine for both systemic and localized conditions.
- Systemic Use: Administered intravenously to treat hypomagnesemia, manage life-threatening arrhythmias (such as torsades de pointes), and act as a muscle relaxant or anticonvulsant in specific toxicities or conditions.
- Gastrointestinal Use: When administered orally, it acts as a potent osmotic cathartic (laxative) to help clear the intestinal tract.
- Topical Use: Frequently used as a hyperosmolar soak or poultice to draw out localized infections, soothe sore muscles, or treat hoof abscesses in large animals.
Clinical Pearl: While highly effective, systemic administration requires careful monitoring of cardiovascular and respiratory status due to the risk of profound CNS and respiratory depression at high doses.
Mechanism of action
Magnesium is a critical intracellular cation and a cofactor for over 300 enzymatic reactions.
- Neuromuscular & CNS: Magnesium competes with calcium at the motor endplate, decreasing acetylcholine release and reducing motor nerve impulse transmission, leading to muscle relaxation and CNS depression.
- Cardiovascular: Acts as a physiological calcium channel blocker, slowing sinoatrial node impulse formation and prolonging conduction time → antiarrhythmic effect.
- Gastrointestinal: Poorly absorbed in the GI tract, it creates an osmotic gradient that draws water into the intestinal lumen → osmotic cathartic effect.
- Topical: Creates a hypertonic environment that draws out fluid and exudate from localized swellings or abscesses.
Safety & warnings
Contraindications
- Renal failure or severe renal impairment
- Heart block or significant myocardial damage
- Myasthenia gravis (can exacerbate weakness)
Adverse effects
- Hypermagnesemia
- Muscle weakness
- Respiratory depression
- Hypotension
- Cardiac arrhythmias or heart block
- Diarrhea (with oral administration)
- Somnolence
- CNS depression
- Coma
- Muscular weakness
- Bradycardia
- Prolonged Q-T intervals
- Neuromuscular blockade
- Cardiac arrest
Precautions
Use with extreme caution in patients with impaired renal function, as magnesium is primarily excreted by the kidneys. Monitor ECG, respiratory rate, and deep tendon reflexes during intravenous administration. Have intravenous calcium (e.g., calcium gluconate) readily available as an antidote for magnesium toxicity.
Drug interactions
Potentiates neuromuscular blockade
Additive CNS depression
Risk of profound hypotension and cardiovascular collapse
Additive CNS depression effects
Additive CNS depression effects
Risk of severe neuromuscular blockage
Serious conduction disturbances can occur
Monitoring
- Serum magnesium concentrations
- Electrocardiogram (ECG)
- Respiratory rate and depth
- Deep tendon reflexes (e.g., patellar reflex)
- Renal function (BUN, creatinine)
- Blood pressure
- Serum magnesium levels
- ECG (for Q-T interval and heart rate)
- Respiratory rate and effort
Pharmacokinetics
Absorption
Poorly absorbed from the intact gastrointestinal tract (acts locally as an osmotic laxative). Rapidly and completely available following intravenous administration.
Distribution
Widely distributed throughout the body; approximately 30% is bound to plasma proteins. Crosses the placenta and is excreted in milk.
Metabolism
Not metabolized; exists in the body as the magnesium ion (Mg2+).
Elimination
Excreted primarily by the kidneys. The rate of excretion is proportional to the serum concentration and glomerular filtration rate.
Overdose
Signs of hypermagnesemia (magnesium toxicity) include loss of deep tendon reflexes, severe muscle weakness, hypotension, respiratory depression, heart block, and potentially cardiac arrest.
Treatment: Discontinue administration immediately. Administer intravenous calcium (e.g., calcium gluconate 10%) slowly to antagonize the cardiovascular and neuromuscular effects. Provide respiratory support (intubation and ventilation) and fluid therapy as needed.
Available products
Formulations
- Injectable solution (e.g., 500 mg/mL)
- Oral powder/granules
- Topical paste/gel
- Crystals for solution (Epsom salts)
- Injectable: 25% w/v solution (1 mEq Mg/ml)
- Injectable: 50% w/v solution (2 mEq Mg/ml)
Veterinary
- Magnesium sulfate injectable solutions
- Magnesium sulfate oral powders/pastes
- Epsom salt poultices (equine)
- Magnesium sulphate injection BP (Vet) 25% w/v
Human-labeled
- Magnesium sulfate injection (e.g., 50%)
- Epsom salt crystals (OTC)
Regulatory status
POM-VPS, POM
POM-VPS, POM
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store at room temperature (15-30°C). Protect injectable solutions from freezing. Keep oral powders and crystals in tightly closed containers to protect from moisture.
Client information
Magnesium sulfate (Epsom salt) is often used at home for soaking sore paws or treating minor localized swellings.
- Topical Soaks: Dissolve the recommended amount in warm water. Do not let your pet drink the soak water, as it can cause severe diarrhea and potential electrolyte imbalances.
- Oral Use: If prescribed as a laxative, expect your pet to have loose stools. Ensure they have constant access to fresh drinking water to prevent dehydration.
- When to Call the Vet: Contact your veterinarian immediately if your pet becomes extremely lethargic, weak, has difficulty breathing, or collapses.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.