Magnesium, Hypermagnesemia

DEFINITION
Dogs—serum magnesium >2.51 mg/dL
Cats—serum magnesium >2.3 mg/dL

PATHOPHYSIOLOGY
Magnesium—second only to potassium as the most abundant intracellular cation; most is found in bone and muscle; required for many metabolic functions
Magnesium is an important cofactor in the sodium-potassium ATPase pump that maintains an electrical gradient across membranes and thus plays an important role in the activity of electrically excitable tissues.
Interference with the electrical gradient can change resting membrane potentials; repolarization disturbances result in neuromuscular and cardiac abnormalities.
Magnesium homeostasis is largely controlled by renal elimination; any condition that severely lowers the glomerular filtration rate can elicit hypermagnesemia.
High magnesium concentration impairs transmission of nerve impulses and decreases the postsynaptic response at the neuromuscular junction.
Magnesium has been called nature's calcium blocker; the most serious complications of hypermagnesemia result from calcium antagonism in the cardiac conduction system.