valproic acid toxicity and ammonia

RAGING HYPOTHETICAL:
--wacky/altered patient, happens to be on valproate, what could be going on?


VALPROIC ACID TOXICITY
--if you're worried about this, your differential for secondary problems/causes can include: cerebral edema, electrolyte abnormalities, hepatotoxicity, and hyperammonemia/encephalopathy


HYPERAMMONEMIA w/VALPROIC ACID:
--can occur after acute toxicity or chronic use
--not always associated with elevated liver function tests
--happens 'cause a metabolite of valproic acid inhibits an enzyme needed for ammonia elimination by the urea cycle (you can look up the names if you really want to)
--valproate may also mess with carnitine, elevate ammonia that way too


BOTTOM LINE:
--wacky patient with valproate on their med list, consider sending an ammonia level and/or checking for asterixis


Reference(s): uptodate.com: valproic acid poisoning, picture