This section is from the book "Introduction To Materia Medica And Pharmacology", by Oliver T.Osborne. See also: The Principles Of Therapeutics.
Magnesium sulphate has no action on the skin or mucous membranes. It is very slowly absorbed, and causes a watery exudate into the intestines resulting in purging.
It is excreted mostly in the faeces and in small amount in the urine.