Butorphanol is a morphinan-type synthetic agonist–antagonist opioid analgesic developed by Bristol-Myers. Butorphanol is most closely structurally related to levorphanol. Butorphanol is available as the tartrate salt in injectable, tablet, and intranasal spray formulations. The tablet form is only used in dogs, cats and horses due to low bioavailability in humans.
Levorphanol is an opioid medication used to treat moderate to severe pain. It is the levorotatory enantiomer of the compound racemorphan. Its dextrorotatory counterpart is dextrorphan.
Morphinan is the prototype chemical structure of a large chemical class of psychoactive drugs, consisting of opiate analgesics, cough suppressants, and dissociative hallucinogens, among others. Typical examples include compounds such as morphine, codeine, and dextromethorphan (DXM). Despite related molecular structures, the pharmacological profiles and mechanisms of action between the various types of morphinan substances can vary substantially. They tend to function either as μ-opioid receptor agonists (opioids), or NMDA receptor antagonists (dissociatives).
Levomethorphan (LVM) (INN, BAN) is an opioid analgesic of the morphinan family that has never been marketed. It is the L-stereoisomer of racemethorphan (methorphan). The effects of the two isomers of racemethorphan are quite different, with dextromethorphan (DXM) being an antitussive at low doses and a dissociative hallucinogen at much higher doses. Levomethorphan is about five times stronger than morphine.
Methorphan comes in two isomeric forms, each with differing pharmacology and effects:
Phenomorphan is an opioid analgesic. It is not currently used in medicine, but has similar side-effects to other opiates, which include itching, nausea and respiratory depression.
Metazocine is an opioid analgesic related to pentazocine. While metazocine has significant analgesic effects, mediated through a mixed agonist–antagonist action at the mu opioid receptor, its clinical use is limited by dysphoric and hallucinogenic effects which are most likely caused by activity at kappa opioid receptors and/or sigma receptors.
Oxilorphan is an opioid antagonist of the morphinan family that was never marketed. It acts as a μ-opioid receptor (MOR) antagonist but a κ-opioid receptor (KOR) partial agonist, and has similar effects to naloxone and around the same potency as an MOR antagonist. Oxilorphan has some weak partial agonist actions at the MOR and can produce hallucinogenic/dissociative effects at sufficient doses, indicative of KOR activation. It was trialed for the treatment of opioid addiction, but was not developed commercially. The KOR agonist effects of oxilorphan are associated with dysphoria, which combined with its hallucinogenic effects, serve to limit its clinical usefulness; indeed, many patients who experienced these side effects refused to take additional doses in clinical trials.
Levophenacylmorphan is a morphinan derivative that acts as an opioid agonist. It has potent analgesic effects and is around 10x more potent than morphine. Adverse effects associated with its use are those of the opioids as a whole, including pruritus, nausea, respiratory depression, euphoria and development of tolerance and dependence to its effects.
Drotebanol (Oxymethebanol) is a morphinan derivative that acts as an opioid agonist. It was invented by Sankyo Company in Japan during the 1970s. It is synthesised from thebaine.
Ro4-1539 (furethylnorlevorphanol) is an opioid analgesic drug from the morphinan series that was discovered by the pharmaceutical company Hoffmann–La Roche in the 1950s. It acts as a potent μ-opioid agonist, and was found to be around 30-60 times more potent than the related drug levorphanol in animal experiments. Although it has high potency, long duration, and good therapeutic index, Ro4-1539 had no particular clinical advantages over other available opioid drugs, and was never commercially marketed.
Racemorphan, or morphanol, is the racemic mixture of the two stereoisomers of 17-methylmorphinan-3-ol, each with differing pharmacology and effects:
Cyclorphan is an opioid analgesic of the morphinan family that was never marketed. It acts as a μ-opioid receptor (MOR) weak partial agonist or antagonist, κ-opioid receptor (KOR) full agonist, and, to a much lesser extent, δ-opioid receptor (DOR) agonist. The drug was first synthesized in 1964 by scientists at Research Corporation. In clinical trials, it had relatively long duration, good absorption, and provided strong pain relief but produced psychotomimetic effects via KOR activation, so its development was not continued.
Naloxonazine is a potent, irreversible μ-opioid receptor antagonist. Naloxonazine forms spontaneously in acidic solutions of naloxazone, and may be responsible for much or all of the irreversible μ opioid receptor binding displayed by the latter.
Dextrallorphan (DXA) is a chemical of the morphinan class that is used in scientific research. It acts as a σ1 receptor agonist and NMDA receptor antagonist. It has no significant affinity for the σ2, μ-opioid, or δ-opioid receptor, or for the serotonin or norepinephrine transporter. As an NMDA receptor antagonist, in vivo, it is approximately twice as potent as dextromethorphan, and five-fold less potent than dextrorphan.
3-Hydroxymorphinan (3-HM), or morphinan-3-ol, is a psychoactive drug of the morphinan family. It is the racemic counterpart to norlevorphanol.
Ketorfanol, or ketorphanol, is an opioid analgesic of the morphinan family that was found to possess "potent antiwrithing activity" in animal assays but was never marketed. It is a 17-cycloalkylmethyl derivative of morphinan and as such, is closely related structurally to butorphanol, cyclorphan, oxilorphan, proxorphan, and xorphanol, which act preferentially as κ-opioid receptor agonists and to a lesser extent as μ-opioid receptor partial agonists/antagonists.
Dimethylaminopivalophenone is an opioid analgesic with a potency ½ that of morphine. It was initially discovered by Russian scientists in 1954 and subsequently rediscovered in the US in 1969. Its LD50 in mice is 83 mg/kg. It has never been marketed commercially.
Oxymorphone-3-methoxynaltrexonazine (OM-3-MNZ) is a morphinan-based opioid that acts as a selective μ-opioid receptor agonist, unlike the closely related mixed agonist-antagonist Oxymorphonenaltrexonazine.
β-Funaltrexamine (β-FNA) is an irreversible opioid antagonist that was used to create the first crystal structure of the μ-opioid receptor. Chemically, it is a naltrexone derivative with a methyl-fumaramide group in the 6-position.
