Valproic acid was first synthesized in 1882 by Beverly S. Burton as an analogue of valeric acid , found naturally in valerian .  Valproic acid is a carboxylic acid , a clear liquid at room temperature. For many decades, its only use was in laboratories as a "metabolically inert" solvent for organic compounds. In 1962, the French researcher Pierre Eymard serendipitously discovered the anticonvulsant properties of valproic acid while using it as a vehicle for a number of other compounds that were being screened for antiseizure activity. He found it prevented pentylenetetrazol -induced convulsions in laboratory rats .  It was approved as an antiepileptic drug in 1967 in France and has become the most widely prescribed antiepileptic drug worldwide.  Valproic acid has also been used for migraine prophylaxis and bipolar disorder. 
This patient appeared to develop a transient and self-limiting acute hepatitis-like injury after both famotidine and cimetidine therapy. The cross reactivity of these two agents was not suspected, based upon the lack of such cross reactivity to hepatic injury between cimetidine and ranitidine. However, in the case shown above, the recurrence was more rapid and perhaps slightly more severe with the “re-exposure” using cimetidine. Typical of H2 receptor blocker induced liver injury was the rapid recovery upon withdrawal. While liver biopsy was not done, in most such instances centrolobular necrosis with inflammation and mild cholestasis is found. This patient may have had mild underlying nonalcoholic fatty liver disease, but this is a common medical condition and probably did not play a role in the clinically apparent liver injury.