Ketobemidone

Ketobemidone is a powerful opioid analgesic. Its potency is equal to morphine, and it also has some NMDA-antagonist properties. This makes it useful for some types of pain that don't respond well to other opioids.

It is used for all types of severe pain, such as postoperative, cancer, kidney stones and fractures.

History
It was first synthesized in 1942 by Eisleb. The first study of it in man was published in 1946, and it was introduced in clinical medicine shortly after.

Chemistry
Ketobemidone is 1-methyl-4-(3-hydroxyphenyl)-4-propionylpiperidine. It is usually available as the hydrochloride, which is a white powder. It is synthesized by alkylating (3-methoxyphenyl)acetonitrile with bis(2-chloroethyl)methylamine, followed by reaction with ethylmagnesiumbromide, and finally O-demethylation with hydrobromic acid.

Pharmacology
Experiments on former addicts indicated it was more addictive than other opioids, so in 1954 the Economic and Social Council took a resolution urging governments to stop manufacture and use of ketobemidone . As a result ketobemidone is mostly used in the Scandinavian countries, with Denmark topping the statistics . This result was not in agreement with clinical observations, and another study in 1958 didn't find it more addictive than morphine. That study noticed that while for morphine the dose for euphoria is the same as that for analgesia, for ketobemidone the analgesic dose was well below the euphoric dose.

Analgesia after 5-10 mg orally or 5-7.5 mg intravenously lasts 3-5 hours. Ketobemidone is also available in preparations with a spasmolytic, which can improve the analgesia.

Ketobemidone is mainly metabolised by conjugation of the phenolic hydroxyl group, and by N-desmethylation. Only about 16% is excreted unchanged.

Pfizer manufactures ketobemidone under the tradenames Ketogan and Ketorax. It is available as tablets, suppositories and injection fluid. A sustained release formulation exists sold as Ketodur in some countries containing 10 or 25 mg ketobemidone.