Dextromoramide


Dextromoramide is a powerful opioid analgesic approximately three times more potent than morphine but shorter acting. It is subject to drug prohibition regimes, both internationally through UN treaties and by the criminal law of individual states. The abuse potential by those who only have mild or no pain does exist, thus responsibility over supply, prescription, and dosage is a touchy subject among the international communities. The most value found in dextromoramide usage apart from an alternative to morphine/diamorphine in palliative care, is the fact that it can palliate cancer pain and suffering without drastically blocking or compromising the bowels through activation of peripheral opioid receptors, as is commonly seen in high doses of fully natural non-synthetic opiates like codeine and morphine, and even hydromorphone in some cases. Usually, it is marketed solely in the Netherlands, while in the UK Diamorphine or morphine are preferred, in the US, hydrocodone and oxycodone are sometimes used, and in the Scandinavian countries, medicines like ketobemidone are available to doctors in such dire cases. Both the US and to a leaser extent, the EU have faced a small problem with opioid abusers creating a stigma or difficulty around prescribing in palliative care and when very strong opioid are indeed indicated. The legal and moral responsibility remains with the prescriber, clinician and to some extent the pharmacist, rather than purely regulatory or government authorities to solely dictate the way in which severe pain and suffering are approached. Some barriers to entry may be required, simply to protect patients or addicts from escalating their usage to an uncontrollable or severely toxic level, this treatening both their life and quality of life, however this does not preclude sparing and even liberal use of palliative medications when they are indicated, to end or lessen severe pain and suffering, including the worst aspect of terminal disease in the physiological sense, as well as in the literal sense - in reference to pain receptors in the central and peripheral nervous system responding to real stimuli. In the case of purely psychological or phaocaomoatic pain, a better approach can include low dose methylphenidate, hydrocodone, or a typical serotonergic antidepressant. However it cannot be denied that in very severe treatment resistant depression that has not responded to any of the typical, atypical, or even off label agents available, then opioid can be trialled with care.

History

Dextromoramide was discovered and patented in 1956 by Dr Paul Janssen at Janssen Pharmaceutica, who also discovered fentanyl, another important synthetic opioid, widely used to treat pain and in combination with other drugs as an anaesthetic, as well as haloperidol, piritramide, the loperamide-diphenoxylate series and other important drugs
Dextromoramide was singled out along with ketobemidone and several other synthetics by the United Nations and European Union as being "extra-dangerous" in the early 1960s, with dextromoramide being alleged to be three times more euphoric than heroin at equianalgesic doses, though this did little to stem production in the first half of the decade. The development of the moramides and the coming to fruition of work on piritramide were two of the events that precipitated the 1961 update to the Single Convention On Narcotic Drugs, as cited by Dr Shulgin in Controlled Substances and various monographs.
Dextromoramide was much favoured by drug users in Australia in the 1970s and the United Kingdom. It has the main proprietary name of Palfium amongst others, though as of mid-2004 the drug was discontinued in the UK due to limited supplies of precursor chemicals. Although this is true, it is believed there was an approximate one year shortage of Dextromoramide and the real reason that Palfium was not put back into production for the UK market is because of how addictive and potent it is as an oral painkiller. Dependence liability is similar to morphine, but with a less severe withdrawal syndrome.
The only European countries that now use the brand Palfium are the Netherlands, Ireland and Luxembourg. It is presumably able to be imported into other Schengen zone countries under Title 76 of said treaty coming into force in 2002. It is a Schedule I Narcotic controlled substance in the United States, with a DEA ACSCN of 9613 and an annual aggregate manufacturing quota of zero as of 2013, and had been out of use in the United States for around a decade when the new Controlled Substances Act 1970 was promulgated. The salts of dextromoramide in use are the hydrochloride and tartrate. Racemoramide and moramide intermediate are also controlled.

Medical use

The main advantage of this drug is that it has a fast onset of action when taken orally, and has a high bioavailability which means that oral dosing produces almost as much effect as injection. It also has a relatively low tendency to cause constipation which is a common problem with opioid analgesics used for cancer pain relief, and tolerance to the analgesic effects develops relatively slowly compared to most other short-acting opioids.

Pharmacokinetics

Dextromoramide has a mean elimination half life of 215.3 +/- 78.4 minutes and volume of distribution of 0.58 +/- 0.20 L/kg. Peak plasma levels are reached within 0.5-4.0 h after dosing, decline of plasma concentrations after the peak follow a biphasic pattern, with half-lives of 0.4-1.6 h for the first phase and 6.3-21.8 h for the terminal phase. While in about 40% of patients, half-lives from 1.5 to 4.7 h, in a monophasic manner. Less than 0.06% of the dose is excreted unchanged in urine within 8 h of administration.

Chemistry

Dextromoramide is the right-handed isomer of the moramide molecule. The left-handed molecule is called levomoramide, and a mixture of the two is called racemoramide. Its full chemical name is -1-pyrrolidine, and its molecular formula: C25H32N2O2, with an atomic weight of ~392.5.
Dextromoramide was discovered during the course of research into a related family of compounds, the α,α-Diphenyl-γ-Dialkyamino-Butyramides, which show no analgesic activity, but are extremely active physiologically as inhibitors of gastric secretions in man. Other drugs from this series show antispasmodic and antihistamine effects, but most research was put into researching analgesics.
The structure-activity relationships of this family of drugs was investigated extensively, with dextromoramide representing the optimisation of several different structural features;
at the 1-amide group only the pyrrolidine and dimethylamide substituents were active, with pyrrolidine being more potent
the alkyl chain was more potent when methylated, 3-methylation was more potent than 4-methylation, and in the 3-methyl analogues the dextro isomer was more active
while morpholine, dimethylamine, pyrrolidine and piperidine were all active at the 4-amine group, morpholine was the most active
any substitution on the phenyl rings reduces activity.
So dextromoramide, with a pyrrolidine ring on the 1-amide position, a dextro methyl group on the 3-position of the alkyl chain, a morpholine ring around the 4-amine group, and both phenyl rings unsubstituted, was by far the most potent out of all the compounds in this series and was the only one that became widely used in medicine.