Opioids Opium

Analgesic Plants Opioid Opium poppy, myrrh... 

Opioids (opium, morphine, heroin, meperidine, methadone, etc) are common drugs of abuse (see Chapters 31 and 32), and overdose is a common result of using the poorly standardized preparations sold on the street. See Chapter 31 for a detailed discussion of opioid overdose and its treatment. 

THC acts at both spinal and supraspinal levels to produce analgesia. As with opioids (opium derivatives), cannabinoids inhibit GABAergic synaptic transmission, while opioids also inhibit post-synaptic neurones. In this way THC and opioids have synergistic analgesic effects. Endogenous cannabinoids (anandamide) produce analgesia, but anandamide is less potent than THC and synthetic cannabinoids (Vaughan and Christie 2002). 

Enkephalins and Endorphins. Morphine (142), an alkaloid found in opium, was first isolated in the early nineteenth century and widely used in patent medicines of that eta. It is pharmacologically potent and includes analgesic and mood altering effects. Endogenous opiates, the enkephalins, endorphins, and dynotphins were identified in the mid-1970s (3,51) (see Opioids, endogenous). Enkephalins and endorphins ate Hsted in Table 9. 

Opioids. Morphine [57-27-2] C yH NO, (8) the most prevalent and analgesicaHy potent of the naturally occurring opium alkaloids (qv), has been used as an anesthetic premedication for over one hundred years (93). It has also been used as an iv analgesic for the last four decades, and, since 1969, in high doses as an anesthetic agent (117). 

In the strict sense, opiates are drugs which are derived from opium and include the natural products morphine, codeine, thebaine and many semi-synthetic congeners derived from them. In the wider sense, opiates are morphine-like drugs with non-peptidic structures. The old term opiates is now more and more replaced by the term opioids which applies to any substance, whether endogenous or synthetic, pqrtidic or non-peptidic, that produces morphine-like effects through an action on opioid receptors. 

Opioid analgesics are the narcotic analgesics obtained from the opium plant. More than 20 different alkaloids are obtained from the unripe seed of the opium poppy... 

Morphine, when extracted from raw opium and treated chemically, yields the semisynthetic narcotics hydromorphone, oxymorphone, oxycodone, and heroin. Heroin is an illegal narcotic in the United States and is not used in medicine. Synthetic narcotics are those man-made analgesics with properties and actions similar to the natural opioids. Examples of synthetic narcotic analgesics are methadone, levorphanol, remifen-tanil, and meperidine Additional narcotics are listed in the Summary Drug Table Narcotic Analgesics. 

The term opioid refers to any exogenous substance that acts as an agonist at any of several receptors. Opioid antagonists are drugs that bind to a receptor but produce no actions. The poppy plant, Papaver somniferum, from which opium is obtained, is grown in many areas of the world. Morphine constitutes 10% of opium, and codeine can be obtained direcdy from opium. Semisynthetic opioids such as heroin and oxycodone are obtained directly or indirectly from morphine. There are other distinct chemical classes of drugs with opioid actions, including the methadones. 

Opioids are easily absorbed subcutaneously and intramuscularly, as well as from the gastrointestinal tract, nasal mucosa (e.g., when heroin is used as snuff), and lung (e.g., when opium is smoked). About 90% of the excretion of morphine occurs during the first 24 hours, but traces are detectable in urine for more than 48 hours. Heroin (diacetyhnorphine) is hydrolyzed to monoacetylmorphine, which is then hydrolyzed to morphine. Morphine and monoacetylmorphine are responsible for the pharmacologic effects of heroin. Heroin produces effects more rapidly than morphine because it is more lipid soluble and therefore crosses the blood-brain barrier faster. In the urine, heroin is detected as free morphine and morphine glucuronide (Gutstein and Akil 2001 Jaffe et al. 2004). 

The word opioid is used to refer to the overall class including the semi- and fully-synthetic agents, but the word opiate only refers to the naturally occurring opioids such as heroin, opium, and morphine. 

When Montgomery and I published our article, we thought we had disproven another theory of placebo effects - the theory that placebo effects are produced by the release of endorphins in the brain. In 1978 researchers at the University of California in San Francisco discovered that when placebos reduce pain, they may stimulate the release of endorphins.18 Endorphins, the existence of which had only been discovered a few years earlier, are opioids that are produced naturally by the brain. Just like the opiates that are derived from opium - morphine and codeine, for example - endorphins reduce the sensation of pain. The University of California researchers reasoned that if placebos can mimic the effects of opiate drugs, maybe they do so by stimulating the release of the brain s endogenous opioids. 

More than 30 alkaloids have been identified in opium (Robbers et al. 1996). The most relevant are morphine (4-21%), codeine (0.8-2.5%), noscapine (4-8%), papaverine (0.5-2.5%), and thebaine (0.5-2%) (figure 8.4). Other opium alkaloids include narceine, protopine, laudanine, codamine, cytopine, lanthopine, and meconidine. Numerous other opioids have been synthesized from opium alkaloids. Among them is heroin, or diacetylmorphine. 

Opioids are administered in several ways. Opium was most commonly taken recreationally by smoking, but intravenous administration has become most common since the isolation of opium alkaloids and invention of the hypodermic needle. The development of heroin from morphine at the turn of the twentieth century led to more intense euphoric effects and greater risk for addiction. Heroin may also be snorted, or it can be smoked when added to a medium such as tobacco. Medically, opioids are commonly given through oral, subcutaneous, intravenous, transdermal, or rectal routes. 

Dams R, Benijts T, Lambert WE, De Leenheer AP. 2002. Simultaneous determination of in total 17 opium alkaloids and opioids in blood and urine by fast liquid chromatography-diode-array detection-fluorescence detection, after solid-phase extraction. J Chromatogr B Analyt Technol Biomed Life Sci 773(1) 53-61. 

Opioids. Activation of opioid receptors in the enteric nerve plexus results in inhibition of propulsive motor activity and enhancement of segmentation activity. This antidiarrheal effect was formerly induced by application of opium tincture (paregoric) containing morphine. Because of the CNS effects (sedation, respiratory depression, physical dependence), derivatives with peripheral actions have been developed. Whereas diphenoxylate can still produce clear CNS effects, loperamide does not Lullmann, Color Atlas of Pharmacology... 

Heroin, the diacetyl derivative of morphine, is the most important illicit drug derived from the opium poppy. Together with heroin and its metabolites, other synthetic (e.g., methadone, tramadol) and semi-synthetic (e.g., buprenorphine) opioids have been quantified in different biological fluid using HPLC. 

The opium alkaloid morphine is representative for this group of opiates and also for other opioid analgesics. Morphine is a full agonist for both the jx and the k receptors. It is used to relieve severe acute pain, or chronic pain in terminally ill patients. Its oral bioavailability varies from 15% to 35% and its... 

The most important other opium alkaloid is codeine. In contrast to morphine, codeine has a high oral-parenteral potency ratio due to less first-pass metabolism. Codeine is considered a prodrug, since it is metabolised in vivo to the primary active compounds morphine and codeine-6-glucuronide. Approximately 10% is demethylated to morphine. The analgesic effect of codeine is due to the formation of these metabolites as codeine itself has a very low affinity for opioid receptors. The half-life of codeine in plasma is 2 hours. 

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