An injection of calcium salt treats an overdose of magnesium sulfate, according to Drugs.com. Also called hypermagnesemia, a magnesium sulfate overdose often requires 10 to 20 milliliters of a 5 percent calcium solution diluted with isotonic sodium chloride.
Drugs.com also states that 0.5 to 1 milligrams of physostigmine injected under the skin can help many patients recover more rapidly from magnesium sulfate intoxication.
Those who are suffering from intoxication or an overdose of magnesium sulfate often experience a sharp drop in blood pressure and respiratory paralysis. Until the proper antidote can be administered, artificial respiration is required to keep the patient alive, states Drugs.com.