Magnesium Hydroxide

What is magnesium hydroxide?

Magnesium hydroxide (Magnalax®, Carmilax®, Polymag®, Rumen Bolus®, Instamag®, Polyox®II, Laxade®) is a drug that may be used in animals as an oral laxative, an antacid, for treatment of low magnesium levels, and for treatment of orally ingested toxins. It may be used in dogs, cats, cattle, sheep, and goats.

Veterinary versions are available over the counter, but there are no FDA-approved versions of magnesium hydroxide for use in animals. 

Products labeled for humans are also used off-label (extra-label) in pets and livestock (Milk of Magnesia, Pedia-Lax®). Combination products with magnesium hydroxide and aluminum are sometimes used as antacids in animals as well (e.g., Maalox® Suspension).

Many drugs are commonly prescribed for off-label use in veterinary medicine. “Off label” means the drug is being used in a way that has not been reviewed or approved by the U.S. Food and Drug Administration (FDA) or Health Canada. In these instances, follow your veterinarian’s directions and cautions carefully, as they may be significantly different from those on the label.

How do I give my pet magnesium hydroxide?

• Magnesium hydroxide is given orally (by mouth)
• Oral formats include liquid bolus or solution, powder tablets, and chewable tablets (Pedia-Lax®).
• This medication may be given with or without food.
• Ensure your pet is properly hydrated before you give magnesium hydroxide to prevent potential complications and side effects.
• Follow your veterinarian’s directions and measure liquid forms of this medication carefully.

This medication should take effect within 1–2 hours, and improvement in clinical signs should follow.

What if I miss giving my pet the medication?

If you miss a dose, give it as soon as you remember, and then continue with the regular dosing schedule. However, if it is almost time for the next dose, skip the missed dose and resume the regular dosing schedule. Do not give the pet two doses at once.

Are there any potential side effects from magnesium hydroxide?

Magnesium hydroxide may cause the following side effects:

• Diarrhea
• Cramping and nausea
• Constipation

Serious adverse reactions may occur. If any of the following signs develop, stop giving magnesium hydroxide and contact your veterinarian immediately:

• Muscle weakness
• Heart rhythm abnormalities
• Central nervous system changes, such as disorientation, seizures, head tilt, and blindness.

Drug sensitivities can develop over time, with repeated exposure. Your pet may have no reaction after the first few doses but may develop a sensitivity later. It is important to watch for signs of an allergic reaction over the entire course of the treatment and notify your veterinarian if you have any concerns.

Other side effects may occur. If you notice anything unusual, contact your veterinarian immediately. This medication is short acting and should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this medication?

DO NOT USE magnesium hydroxide in:

• Pets that are allergic to it
• Pets with severe kidney disease

USE WITH CAUTION in:

• Pets that are on magnesium restricted diets
• Pets with restrictions to the stomach opening (gastric outlet obstruction)

Are there any drug interactions I should be aware of?

Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking before starting any new treatment.

The following drugs should be USED WITH CAUTION when given with magnesium hydroxide:

• Aminoglycoside antibiotics (e.g,, amikacin, gentamicin)
• Quinidine
• Sodium polystyrene sulfonate
• Sustained or extended-release medications (magnesium hydroxide may alter the absorption of these drugs by speeding up the time it takes the drugs to pass through the gastrointestinal system)
• Sympathomimetic agents (drugs that mimic the stimulation of the sympathetic nervous system)
• Tacrolimus

The following drugs should be given at least two hours apart from magnesium hydroxide when both drugs are being given by mouth:

• Allopurinol
• Aspirin
• Azole antifungals (e.g., ketoconazole, itraconazole)
• Beta-blockers (e.g., atenolol)
• Cefpodoxime
• Corticosteroids (e.g., dexamethasone, prednisone)
• Digoxin
• Ethambutol
• Fexofenadine
• Fluroquinolones (e.g., ciprofloxacin, enrofloxacin, marbofloxacin)
• Gabapentin
• H2 antagonists (e.g., famotidine, ranitidine)
• Iron salts
• Isoniazid
• Ketoconazole
• Levothyroxine
• Macrolides (e.g., azithromycin)
• Misoprostol
• Mycophenolate mofetil
• Penicillamine
• Phenytoin
• Rifampin
• Solatol
• Tetracyclines (e.g., doxycycline, minocycline)

Is any monitoring needed with this medication?

• In cattle, rumen pH should be determined before use, as oral magnesium hydroxide should only be used with documented rumen acidosis.
• Monitor electrolytes and acid-base status in patients receiving high-doses of magnesium hydroxide or long-term therapy.
• Your veterinarian will let you know when and how they want to reassess your pet to ensure the medication is working and not causing side effects.
• At home, monitor for any side effects such as those noted above. If any occur, stop using the medication and contact your veterinarian.

How do I store magnesium hydroxide?

• Ensure magnesium hydroxide is tightly stored in its original container.
• Store this medication at room temperature in a cool, dry place, protected from light.
• Do not store above 86°F (30°C).
• Keep the container out of reach of children and pets.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility. Be prepared to provide information about the product and your pet’s weight and symptoms.