The toxicity of magnesium nitrate when given by mouth

It is a daily experience that large doses of magnesium sulphate can be taken by mouth without any other than a purgative effect. I have given to rabbits, by mouth, 7 grams or more of magnesium sulphate (in molecular solution) per kilo, without any unfavorable effects. The same applies also to magnesium chloride and some other magnesium salts. I have, however, discovered that magnesium nitrate when given by mouth is capable of producing a toxic effect like that of magnesium salts when introduced subcutaneously.

When a dose of 6 grams per kilo in molecular solution is given by mouth to a rabbit, the animal soon becomes paralyzed and narcotized and dies in thirty or forty minutes of respiratory paralysis. Fifteen or twenty minutes after the administration, the appearance and behavior of the animal is exactly like that of one which received magnesium sulphate subcutaneously (2 grams per kilo). A dose between 4 and 5 grams per kilo causes in general the same symptoms but in a gradual way; the animal dies after five or six hours. A dose of between 3 and 4 grams causes no serious effects, but for six or eight hours after its administration the animal remains in a soporous state; it sits in one place with eyes closed and head drooping; a loud noise wakes it up and it attempts to move about or to eat, but in a few minutes it falls asleep again.

This toxicity of the magnesium nitrate is apparently due to its greater absorptioll from the gastro-intestinal canal. It is certainly not due to its diminished elimination through the kidneys; on the contrary it acts in some degree as a diuretic, and, when given by subcutaneous injection, the animal withstands a somewhat greater proportionate dose of the nitrate than of the sulphate or chloride, probably because the nitrate increases somewhat the diuresis.