Why Lithium stoppage becomes headache?

Discussion in 'NEET 2013 All india Exam' started by samuel, Nov 5, 2014.

  1. samuel

    samuel New Member

    1)Lithium half life is 24 hours.

    2)only 10% of lithium is protein bound in plasma.Remaining 90% is free.

    3)Remember, free plasma drugs are nothing but charged particles/soluble/hydrophilic/volume of distribution only in water compartment/slow to cross over through BBB/mostly metabolized and cleared by kidney/and are generally have low Therapeutic Index(meaning,the difference in dose between toxic dose and therapeutic dose is too small,so that even a little increase beyond therapeutic dose can be lethal).

    4)Lithium MOA== Interacts with G protein coupled receptors,specifically Gq.

    5)Remember, Gq is involved predominantly in CNS,enteric,anything that is related to secretion and smooth muscle contractions. Gq acts through PIP2 second messenger.

    6) Lithium inhibits the recycling of PIP2,so that none of the above functions could be carried out. So in terms of specific receptors M1,M3,,H1,Alpha1,V1 are the ones they interact predominantly. So all functions related to the above receptors are either diminished or atleast partially dysfunctional. V2 is Gs,but this is an exception,becos lithium also acts on V2,by decreasing cAMP.So this would cause the ADH receptors to malfunction thereby increasing water excretion.So we know lithium cause NI.

    7)Since half life of lithium is 24 hours, we need atleast 24 hours to bring down the blood levels of lithium. So for sure atleast 1 day prior to surgery the med should be stopped. But,in 24 hours only half the drug is cleared and still 50% more is in the plasma.That might take another 24 hours to clear.So logical answer would be 2 days before surgery.

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