I had a good look at diethylpentAnamide too. But the German literature on the subject, allbeit limited, consistently uses diäthylpentEnamid or diethylpentEnamid. Synonyms Diethylallylacetamid, Pentenamid according to
http://www.toxcenter.de/stoff-infos/d/diethylpentenamid.pdf
I have no idea if this is the same molecule as pentAnamide. The drug was used in Germany as a sedative-hypnotic and was apparently good for suicide.
It is true that there are a number of pentAnamides used as sed-hyps and anti-epileptics (e.g. Valpromide).