Magnesium is very important positive ion that is vital for many cellular processes. The majority of the magnesium in the body is found inside the cells, especially the bones, but about 1 % circulates in the blood stream, either as an active ion (55%) or bound to proteins and other complex molecules. Excess magnesium in the blood, called hypermagnesemia, can be a very serious problem since magnesium limits the function of calcium ions. This leads to muscle weakness, abnormal heart rhythms, and eventually respiratory paralysis and cardiac arrest. Magnesium is normally excreted by the kidneys. In dogs, normal kidney function will maintain a typical magnesium serum concentration below 2.5 mg/dl, even if high levels of magnesium are ingested. Severe renal failure is the most common reason for blood magnesium levels to rise. This is frequently a problem if dogs with kidney failure receive IV fluids high in magnesium. Some endocrine imbalances or a pericardial effusion (fluid inside the heart cavity) can also cause hypermagnesemia. Magnesium levels may rise temporarily from an overdose of a magnesium containing medication, like laxatives or antacids, or due to blood or muscle cell destruction that liberates a large amount of intracellular magnesium into the blood. Hypermagnesemia is less common in dogs than magnesium deficiency, but when it does occur, it can be associated with life-threatening problems. Administration of IV fluids and other electrolytes can correct the immediate symptoms, however, dogs with kidney failure or heart failure still often end up being euthanized.

About 1% of the magnesium in the body circulates in the blood as a positive ion. Magnesium works in combination with other electrolytes to manage many cellular processes. Excess magnesium, called hypermagnesemia, upsets the normal balance between ions and causes serious life-threatening symptoms.

Mild hypermagnesemia can often be asymptomatic, but very high levels will present serious life-threatening symptoms that should be treated as an emergency.

The veterinarian will categorize your dog’s hypermagnesemia based on its severity.

The following conditions are often associated with hypermagnesemia.

A blood test will measure the total serum concentration of magnesium as well as the concentration of magnesium ions (generally considered more accurate since this is the active form of magnesium). Other electrolytes levels will be measured at the same time since ions in the blood frequently interact and other conditions like hypocalcemia and hyperkalemia can cause similar symptoms. 

The veterinarian will try to determine the underlying cause of the problem. Urinalysis will test kidney function and determine if magnesium is being excreted effectively. Hormone imbalances will often be visible on a blood test. Other tests may be ordered to check the function of certain glands. An echocardiogram will evaluate heart function and diagnose fluid in the pericardial cavity.

Overuse of laxatives or overdose on human medications can cause hypermagnesemia. The veterinarian will need to know if your dog has been exposed to these drugs, especially if other tests come back negative. If no other cause is found, a second blood test may be necessary since false positives can happen due to red blood cells bursting during the testing process.

Treatment will depend on the severity of your dog’s condition. Mild hypermagnesemia is treated with intravenous sodium chloride solution. Furosemide, a diuretic that increases magnesium excretion, will be given unless the dog is dehydrated.

Severe life-threatening hypermagnesemia will be countered by injection of calcium gluconate. Excess magnesium in the blood can block calcium, so rebalancing these two electrolytes helps to restore neuromuscular function quickly. Heart rate and blood pressure will be monitored carefully during administration. Regular doses of oral physostigmine can also help counter the negative actions of excess magnesium. 

Other treatments will focus on the cause of the problem. Hypermagnesemia is often associated with complete kidney shut-down, so there may be little the vet can do to treat your dog at this stage of kidney failure. Dialysis or medication to support kidney function could be ordered and life-threatening symptoms will be managed as much as possible.

Treatment of pericardial effusion will depend on the cause. Many conditions including infection, cancer, or an inherited abnormality can be related. Pericardiocentesis may be necessary to remove fluid from the heart. Antibiotics, surgery, or other treatments could also be ordered. If hypermagnesemia is due to a temporary condition like an overdose of laxatives or antacids it will usually resolve itself with treatment of the immediate symptoms. Vomiting may be induced to reduce absorption in cases of recent poisoning.

Your dog’s recovery from hypermagnesemia will depend on the cause and the severity of the condition. Dogs may recover from temporary problems like overdose. If the condition is due to severe kidney failure or heart failure, however, treatment may not be possible and the veterinarian may recommend euthanasia. Your dog’s prognosis will depend on the diagnosis of a veterinarian.