Pharmacology: Magnesium is the second most plentiful cation of the intracellular fluids. It is essential for the activity of many enzyme systems and plays an important role with regard to neuro-chemical transmission and muscular excitability. Deficits are accompanied by a variety of structural and functional disturbances. Some of the effects of magnesium in the extracellular fluid cause depression of the central nervous system. Magnesium has a direct depressant effect on skeletal muscle. Abnormally low concentrations of magnesium in the extracellular fluid result in increase acetylcholine release and increase muscle excitability that can produce tetany.
Magnesium slows the rate of S-A nodal impulse formation. Higher concentration of magnesium (greater than 15 mEq/L) produces cardiac arrest in diastole.
Excess magnesium causes vasodilation by both a direct action on blood and ganglionic blockade.
Magnesium is exerted principally by glomerular filtration.