Magnesium Hydroxide
Magnesium hydroxide is used orally as an antacid or cathartic, including ruminal antacid use in cattle.
Group
Osmotic laxative and antacid
Mechanism of Action
Neutralizes acid and retains intestinal water osmotically.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Antacid | 400–800 mg/animal | PO | Every 4–6 h | Equivalent to 5-10 mL of the 400 mg/5 mL suspension. |
| Cathartic | 1200–4000 mg/animal | PO | Every 24 h | Equivalent to 15-50 mL of 400 mg/5 mL suspension. |
| GI-disease-associated magnesium replacement | 400–1200 mg/animal | PO | Every 24 h | Equivalent to 5-15 mL/day of 80 mg/mL milk of magnesia; reassess magnesium, calcium and stool tolerance. |
| Antacid | 400–2400 mg/animal | PO | Every 12–24 h | Separate 5-30 mL alternative for 80 mg/mL product. |
| Cathartic | 80–1600 mg/animal | PO | Equivalent to the listed 1-20 mL milk-of-magnesia range; no repeat frequency is supplied. |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Antacid | 400–800 mg/animal | PO | Every 4–6 h | Equivalent to 5-10 mL of the 400 mg/5 mL suspension. |
| Cathartic | 160–480 mg/animal | PO | Every 24 h | Equivalent to 2-6 mL of 400 mg/5 mL suspension; oral route is established by the monograph context. |
| Antacid | 400–1200 mg/animal | PO | Every 12–24 h | Separate 5-15 mL alternative for 80 mg/mL product. |
| Cathartic | 80–400 mg/animal | PO | Equivalent to 1-5 mL milk of magnesia; no repeat frequency is supplied. |
Sheep
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Antacid and cathartic | 1 g/kg | PO | Once | Use the mass instruction rather than the conflicting adult bolus-count example. |
Cattle
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Antacid and cathartic | 1 g/kg | PO | Once | Use the mass instruction rather than the conflicting adult bolus-count example. |
| Documented rumen acidosis | Reference only | PO | Adult: up to 1 g/kg mixed in 2-3 gallons warm water by stomach tube; smaller repeats may be considered in 6-12 hours. If rumen contents were evacuated, initial total must not exceed 225 g. Correct dehydration and systemic acidosis concurrently. Calf and sheep/goat directions use 1/8-1/4 of the adult amount but lack a complete independent weight-based prescription. |
Indications
- Constipation
- Antacid treatment
Contraindications
- Renal impairment may cause magnesium accumulation.
- Dehydration
- In ruminants restrict clinical antacid use to documented rumen acidosis rather than undiagnosed rumen dysfunction; avoid magnesium-containing antacids with renal disease.
Interactions
- Decreases absorption of fluoroquinolones and other drugs susceptible to magnesium chelation.
Adverse effects
- Diarrhoea, dehydration and electrolyte losses
- Hypermagnesaemia
Toxicity
Stop treatment if weakness or excessive diarrhoea occurs; assess magnesium and renal function.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Milk of Magnesia 400 mg/5 mL | Oral Liquid | 400 mg / 5 mL | PO |
| Magnesium hydroxide 27 g bolus | Tablet | 27 g / tablet | PO |
| Magnesium hydroxide 90 g bolus | Tablet | 90 g / tablet | PO |
| Magnesium hydroxide concentrated 160 mg/mL | Oral Liquid | 160 mg / mL | PO |
Monitoring and Administration
Administer only to adequately hydrated patients and monitor electrolytes with repeated use.
The powder concentration and its stated equivalence are inconsistent; do not substitute powder volumes without the actual product composition.
The powder-mixing example uses 0.45 kg powder in 1 gallon water, administering 500 mL per 45 kg. This is a product recipe, not a verified pure-ingredient concentration. Polyox volume instructions are 180 mL below 225 kg or 360 mL above 225 kg, but composition is not supplied.
Foal ulcer adjunct uses 15 mL of a specific aluminium/magnesium hydroxide suspension four times daily; ingredient concentrations are not given, so this cannot be treated as magnesium hydroxide alone. Store milk of magnesia below 35°C and do not freeze.