Magnesium Sulfate
Magnesium sulfate has different veterinary roles according to the route. Oral preparations act as saline cathartics, while parenteral products replace magnesium in deficient patients and support treatment of selected arrhythmias. Important applications include hypomagnesemia in critically ill small animals or livestock and specialist management of refractory ventricular rhythm disturbances.
Group
Magnesium replacement, antiarrhythmic and cathartic
Mechanism of Action
Parenteral magnesium restores a cation required for ATP-dependent enzymes, ion-pump function and normal neuromuscular activity. Effects on membrane stability, calcium flux and repolarization can suppress selected arrhythmias, especially when magnesium deficiency contributes. Orally, poorly absorbed magnesium sulfate increases luminal osmotic activity, retaining water and promoting intestinal distension and evacuation.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Cathartic electrolyte-dose alternative | Reference only | PO | 1-2 mEq/kg/day (0.5-1 mmol/kg/day) of magnesium. The parent ingredient is magnesium sulfate mass; ionic and salt units must not be interchanged automatically. | |
| Cathartic | 8–25 g/animal | PO | Every 24 h | |
| Magnesium deficiency or arrhythmia | Reference only | IV | 0.2-0.3 mEq/kg magnesium (0.1-0.15 mmol/kg), delivered at 0.12 mEq/kg/min (0.06 mmol/kg/min); this ion-based dose is not magnesium sulfate milligrams. | |
| Ongoing magnesium replacement | Reference only | IV | 0.2-1 mEq/kg/day magnesium as a constant infusion. Separate fluid-supplement recommendation: 0.75-1 mEq/kg/day. Determine product magnesium-ion content before mixing. | |
| Cathartic | 5–25 g/animal | PO | Single-administration range with no repeat interval supplied. | |
| Cathartic | 2–60 g/animal | PO | Distinct broader historical range; individual hydration and electrolyte assessment is essential. | |
| Refractory ventricular arrhythmia | 30 mg/kg | IV | Magnesium sulfate salt mass, administered slowly; not 30 mg of elemental magnesium. |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Cathartic | 2–5 g/animal | PO | Every 24 h | |
| Magnesium deficiency or arrhythmia | Reference only | IV | 0.2-0.3 mEq/kg magnesium (0.1-0.15 mmol/kg), delivered at 0.12 mEq/kg/min (0.06 mmol/kg/min); this ion-based dose is not magnesium sulfate milligrams. | |
| Ongoing magnesium replacement | Reference only | IV | 0.2-1 mEq/kg/day magnesium as a constant infusion. Separate fluid-supplement recommendation: 0.75-1 mEq/kg/day. Determine product magnesium-ion content before mixing. | |
| Refractory ventricular arrhythmia | 30 mg/kg | IV | Magnesium sulfate salt mass, administered slowly; not 30 mg of elemental magnesium. |
Cattle
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Hypomagnesaemia — Initial | 2–3 g/animal | IV | Administer over 10 minutes. | |
| Hypomagnesaemia — Maintenance | 50–100 g/animal | SC | Source follow-on is 200-400 mL of 25% magnesium sulfate; use appropriate injection-site distribution. Concentrated SC sulfate can cause necrosis; conflicting route-safety guidance requires a product-specific alternative. | |
| Cathartic | 1–2 g/kg | PO | No repeat interval supplied. | |
| Grass-tetany IV treatment | Reference only | IV | Adult beef-cow example: 100 mL of 25% Epsom-salt solution slowly over at least 5 minutes; the stated maximum 0.04 mL/kg/min corresponds to 10 mg/kg/min of salt, not elemental magnesium. Prefer an appropriate proprietary combined calcium/magnesium preparation when indicated. | |
| Emergency colonic magnesium replacement | Reference only | RECTAL | After clearing rectal contents, deliver 60 g magnesium sulfate heptahydrate in 200 mL water into the descending colon, then retain for about 5 minutes. Hyperosmolar mucosal injury and premature evacuation are risks; this is an emergency procedure, not routine laxative dosing. |
Horses
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Cathartic | 1 g/animal | PO | Every 12–24 h | |
| Ventricular arrhythmia | 2–4 mg/kg | IV | Assess ECG response and delivery rate. | |
| Refractory ventricular tachycardia | Reference only | IV | Infuse 1 g/min to a maximum total of 25 g. This fixed-rate infusion must be measured in grams per minute, rather than treated as a per-kilogram rate. Alternative: 4 mg/kg boluses every 2 minutes, or 2 mg/kg/minute infusion, with cumulative total no greater than 50 mg/kg. Track the full cumulative dose; do not mix with calcium-containing fluids. | |
| Cathartic | 0.2 g/kg | PO | Up to 3 days; Diluted in 4 L warm water by nasogastric tube; only after rehydration, preferably with IV fluid support. Do not continue beyond 3 days. | |
| Cathartic | 1 g/kg | PO | Every 24–48 h | Rehydrate before giving to a colic patient. |
| Caecal impaction adjunct | 1 g/kg | PO | Dissolve in water and give by nasogastric tube with an individualized IV balanced-fluid plan. | |
| Magnesium replacement infusion | 1.0416666667–6.25 mg/kg/hour | IV | Continuous | Exact hourly equivalent of total 25-150 mg/kg/day diluted in compatible IV fluid. |
| Magnesium maintenance infusion | 4.1666666667–6.25 mg/kg/hour | IV | Continuous | Foal/adult total 100-150 mg/kg/day, adjusted to magnesium results. |
| Chronic magnesium replacement | 80–100 mg/kg | PO | Every 24 h | Magnesium sulfate salt mass; distinct from magnesium oxide/carbonate doses. |
| Perinatal-asphyxia adjunct — Loading | 50 mg/kg | IV | Foals: dilute to 1% and administer over 1 hour. | |
| Perinatal-asphyxia adjunct — Maintenance | 25 mg/kg/hour | IV | Continuous | Up to 3 days; After loading; continue 24 hours to 1-3 days with serum-magnesium guidance. |
Pigs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Cathartic | 1–2 g/kg | PO | No repeat interval supplied. |
Birds
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Lead-intoxication cathartic adjunct | Reference only | PO | 0.5-1 g/kg as a 5% drinking-water preparation; actual intake and the intoxication plan determine administration. |
Indications
- Parenteral replacement of magnesium in deficient veterinary patients, including selected critically ill dogs and cats.
- Treatment of hypomagnesemia in cattle, sheep or other livestock, commonly within a balanced mineral-replacement plan.
- Adjunctive treatment of selected refractory ventricular arrhythmias, including magnesium-responsive polymorphic ventricular tachycardia.
- Oral cathartic treatment of selected constipation or impaction syndromes.
- Bowel evacuation before selected veterinary procedures.
Contraindications
- Renal impairment increases magnesium accumulation risk.
- Parenteral magnesium in myocardial damage or heart block; accumulation risk is increased with renal dysfunction.
Interactions
- Do not mix with calcium-, bicarbonate- or lactate-containing solutions.
- Magnesium reduces oral fluoroquinolone absorption.
Adverse effects
- Weakness, hypotension, vomiting and diarrhoea
- Severe excess causes respiratory paralysis and cardiac conduction abnormalities
Toxicity
Stop magnesium, support ventilation and circulation, and assess ECG, electrolytes and renal function urgently.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Magnesium sulfate crystals | Powder | 1 g / g | PO |
| Magnesium Sulfate 250 mg/mL injection Salt-mass concentration only. Dilute below 20% for IV use; do not infer magnesium ion mEq from salt mass without a verified hydrate basis. | Injection | 250 mg / mL | IV, SC |
| Magnesium Sulfate 500 mg/mL injection Salt-mass concentration only. Dilute below 20% for IV use; do not infer magnesium ion mEq from salt mass without a verified hydrate basis. | Injection | 500 mg / mL | IV, SC |
Monitoring and Administration
Monitor ECG for bradycardia, prolonged QT or widening QRS during IV delivery; measure magnesium, calcium, potassium and renal function.
Dilute IV solutions below 20% with an appropriate compatible diluent. Correct concurrent hypocalcaemia separately; do not combine calcium and sulfate solutions.
Electrolyte doses are expressed as magnesium ion mEq or mmol; mass doses are magnesium sulfate salt. A verified hydrate and ion-equivalent basis is required before converting between these units.
Descriptions conflict on subcutaneous concentrated magnesium sulfate: one recommends it while another reports skin necrosis and advises only suitable combined calcium/magnesium products SC. Do not give the earlier 25% SC recipe automatically. The “hexahydrate 8.1 mEq/g” wording conflicts with the heptahydrate identity elsewhere; no salt-to-ion conversion is inferred.
Other ruminant protocols pair 250 mL 25% calcium borogluconate with 100 mL 10% magnesium sulfate IV, followed by sustained replacement; separate calcium first if no proprietary compatible mixture is used. Sheep/goat volumes are 50-100 mL of the specified combination. A calf milk-tetany entry lists 100 mL of 10% sulfate without its route, followed by age-specific oral magnesium oxide. Swine malignant-hyperthermia treatment describes incremental 1 g slow-IV sulfate doses to effect, without a universal total cap.