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Posts Tagged ‘magnesium’

Human body is a collection of trillions of cells.  Life  is nothing but , a bundle of energy flowing across each of these cells  .Every  organ  has a  specailised mode of communication among themselves and others. When a cell is in an excited state , there is a  likelihood of spontaneous electrical activity.This can happen in nerve cells, cardiac cells , GI tract,  or virtually in  any cell  which has a porous cell membrane and ionic fluxes across it .

  • Each cell membrane has a resting membrane potential . It  varies between -60 to – 90mv in most cells. When this potential increases there a propensity for  arrhythmias in heart  and convulsions in the brain , peristalsis in intestines and so on .
  • Drugs  like local anesthetic lignociane acts by blocking the  Na+ channels and there by neural activation .Similarly magesium  acts on these channels to reduce the excitability of these cells.
  • We know,  the sharp ascending stroke of cellular  action potential is mediated by Na + .Blockage of this channel blunts the action potential voltage and thus  the  early and late after depolarisation is prevented
  • Magnesium sulphate’s anticonvulsant action is directly  attributable  to this membrane stabilising action

Thus , membrane stabilising action  can be termed as “membrane sedating”  action

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Magnesium is a powerful cell membrane stabilizing agent. It is well recognized to act on the cerebral motor cortical cells and  suppress seizure , especially in eclampsia of pregnancy .

Mg SO4 is still the drug of choice for seizures of pregnancy. It  was soon realised  ,  the  molecular basis of  cellular excitability    is    similar  for  every cell  . And  thus , we got this  great antiarrhythmic drug !

  • Magnesium is a  cofactor in the enzyme Na /K ATPase in the myocyte cell membrane
  • Integrity of this enzyme is essential for proper maintenance of the intracellular potassium levels.
  • Many times hypokalemia can not be  fully corrected by administration of K + alone .
  • Co- administration of magnesium  increase the intracellular K +    and hyperpolarize the cells and make  it less excitable.
  • Further , magnesium competes with ca++  ions  to enter the cells and thus   it is a natural calcium blocker. This property also helps in controlling refractory calcium dependent  cardiac arrhythmia.

Indications for magnesium

  • Torsades de pointes . Note:  Magnesium does not shorten the QT interval significantly but still effective in torsades.
  • Any refractory VT especially , post MI.
  • Digoxin induced , hypokalemia dependent atrial tachycardias, MAT

It is administered 1-2mg boluses of 2-3 boluses.

Where we should not use magnesium ?

Routine Use of magnesium in recurrent non sustained VT following MI is not recommended .(Courtesy ISIS -4 trial )

Reference

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1368485/

Magnesium : Nature’s own calcium blocker

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1368485/

ISIS 4

Some think ISIS 4 was a delibrate attempt to defame magnesium !

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