Ethinamate was used to treat insomnia (trouble in sleeping) under the brand name VALMID, but then was replaced by other more efficacy medicines. The mechanism of action was not known. However, was studies, which showed that ethinamate inhibits carbonic anhydrases I and did not inhibit II. Nevertheless, even inhibition carbonic anhydrases I is not sufficiently strong to implicate carbonic anhydrases I in the mechanism of action.

Ethinamate:
https://drugs.ncats.io/drug/IAN371PP48

Ethinamate is used to treat insomnia (trouble in sleeping). However, it has generally been replaced by other medicines for the treatment of insomnia. If ethinamate is used regularly (for example, every day) to help produce sleep, it is usually not effective for more than 7 days. Also, if retreatment is necessary, intervals of 1 or more weeks should elapse between periods of treatment. Structurally, it does not resemble the barbiturates, but it shares many effects with this class of drugs; the depressant effects of ethinamate are, however, generally milder than those of most barbiturates. Continued and inappropriate use of ethinamate can lead to tolerance and physical dependence, with withdrawal symptoms very similar to those of the barbiturates.

Excerpt from Drug Information System:
http://www.druginfosys.com/drug.aspx?drugcode=1914&type=1

It is reported that Elvis was found with ten times the standard amount of codeine in his body. He was also reportedly addicted to a variety of substances, such as diazepam, methaqualone, phenobarbital, ethchlorvynol and ethinamate. The toxicology report concluded, at the time, that 'the strong possibility is that these drugs were the major contribution to his demise'. But modern medical advancements now suggest that his underlying heart problems were exacerbated by the heady concoction of drugs found in his system - but they were not a direct cause.

Excerpt from Metro:
https://metro.co.uk/2017/08/16/how-did-elvis-presley-die-myth-and-legend-explored-as-the-king-is-remembered-40-years-on-6850638/

Ethinamate has been replaced by other medicines (particularly benzodiazepines), and it is not available in the Netherlands, the United States or Canada.