Information AboutOpioid |
Although the term '' Opiate '' is often used as a synonym for ''opioid'', it is more properly limited to the natural opium alkaloids and the semi-synthetics derived from them. PHARMACOLOGY See Also: opioid receptor Opioids bind to specific opioid receptors in the central nervous system and in other tissues. There are three principal classes of s acting on GABA ergic Neurotransmission . The Pharmacodynamic response to an opioid depends on which receptor it binds, its affinity for that receptor, and whether the opioid is an Agonist or an Antagonist . For example, the Supraspinal analgesic properties of the opioid agonist Morphine are mediated by activation of the μ1 receptor, respiratory depression and Physical Dependence (dependency) by the μ2 receptor, and sedation and spinal analgesia by the κ receptor. USES Clinical use Opioids have long been used to treat acute pain (such as post-operative pain). They have also found to be invaluable in Palliative Care to alleviate the severe, chronic, disabling pain of terminal conditions such as Cancer . Contrary to popular belief, high doses are ''not'' required to control the pain of advanced or end-stage disease, with the median dose in such patients being only 15mg oral morphine every four hours (90mg/24 hours), i.e. 50% of patients manage on lower doses. In recent years there has been an increased use of opioids in the management of non-malignant Chronic Pain . This practice has grown from over 30 years experience in Palliative Care of long-term use of strong opioids which has shown that dependence is rare when the drug is being used for pain relief. United States The sole clinical indications for opioids in the United States, according to ''Drug Facts and Comparisons,'' 2005, are
In the U.S., doctors virtually never prescribe opioids for psychological relief (with the narrow exception of anxiety due to shortness of breath), despite their extensively reported psychological benefits. There are virtually no exceptions to this practice, even in circumstances where researchers have reported opioids to be especially effective and where the possibility of addiction or diversion is very low—for example, in the treatment of senile dementia, geriatric depression, and psychological distress due to chemotherapy or terminal diagnosis (see Abse; Berridge; Bodkin; Callaway; Emrich; Gold; Gutstein; Mongan; Portenoy; Reynolds; Takano; Verebey; Walsh; Way). Use of opioids in palliative care The current key text for palliative care is the ''Oxford Textbook of Palliative Medicine'', 3rd ed. (Doyle, D., Hanks, G., Cherney, I., and Calman, K., eds., Oxford University Press, 2004). This states that the indications for opioid administration in palliative care are
Not just opioids... In palliative care opioids are always used in combination with adjuvant analgesics (drugs which have an indirect effect on the pain), and as an integral part of care of the whole person. Contraindications for opioids In palliative care, opioids are not recommended for sedation or anxiety because experience has found them to be ineffective agents in these roles. Some opioids are relatively contraindicated in renal failure because the of accumulation of the parent drug or their active metabolites (e.g. morphine and oxycodone). Age (young or old) is not a contraindication to strong opioids. History Non-clinical use was criminalized in the U.S by the Harrison Narcotics Tax Act of 1914 , and by other laws worldwide. Since then, nearly all non-clinical use of opioids has been rated zero on the scale of approval of nearly every social institution. However, in United Kingdom the 1926 report of the Departmental Committee on Morphine and Heroin Addiction under the Chairmanship of the President of the Royal College of Physicians reasserted medical control and established the "British system" of control—which lasted until the 1960s; in the U.S. the Controlled Substances Act of 1970 markedly relaxed the harshness of the Harrison Act. Before the twentieth century, institutional approval was often higher, even in Europe and America. In some cultures, approval of opioids was significantly higher than approval of alcohol. Global shortage of poppy-based medicines Morphine and other poppy-based medicines have been identified by the World Health Organisation as essential in the treatment of severe pain. However, only six countries use 77% of the world's morphine supplies, leaving emerging countries in particular, lacking in pain relief medicine.http://www.senliscouncil.net/modules/publications/008_publication. The current system of supply of raw poppy materials to make poppy-based medicines is regulated by the International Narcotics Control Board under the provision of the 1961 Single Convention On Narcotic Drugs . The amount of raw poppy materials that each country can demand annually based on these provisions must correspond to an estimate of the country's needs taken from the national consumption within the preceding two years. In many countries, underprescription of morphine is rampant because of the high prices and the lack of training in the presciption of poppy-based drugs. The World Health Organisation is now working with different countries' national administrations to train healthworkers and to develop national regulations regarding drug prescription in order to facilitate a greater presciption of poppy-based medicines.The World Health Organisation "Assuring Availability of Opioid Analgesics" {Link without Title} Another idea to increase Morphine availability is proposed by the Senlis Council , who suggest, through their proposal for Afghan Morphine , that Afghanistan could provide cheap pain relief solutions to emerging countries as part of a second-tier system of supply that would complement the current INCB regulated system by maintaining the balance and closed system that it establishes while providing finished product Morphine to those suffering from severe pain and unable access poppy-based drugs under the current system. ADVERSE EFFECTS For more information seeOxford Textbook of Palliative Medicine, 3rd ed. (Doyle D, Hanks G, Cherney I and Calman K, eds. Oxford University Press, 2004). and the online palliative care formulary (available on Palliativedrugs.com ). Common adverse reactions in patients taking opioids for pain relief: These include: nausea and vomiting, drowsiness, dry mouth, Miosis , and constipation. Fortunately, most of these are not a problem (see Treating Opioid Adverse Effects below). Infrequent adverse reactions in patient taking opioids for pain relief: These include: dose-related respiratory depression (see below), confusion, hallucinations, Delirium , Urticaria , Hypothermia , Bradycardia / Tachycardia , Orthostatic Hypotension , dizziness, headache, urinary retention, ureteric or biliary spasm, muscle rigidity, myoclonus (with high doses), and flushing (due to histamine release, except fentanyl and remifentanil). Other adverse effects: A phenomenon of Opioid-induced Hyperalgesia has been proposed, whereby individuals using opioids to relieve pain may paradoxically have more pain as a result of their medication. However, it has not been reported to have been seen in Palliative Care where there is the greatest experience of the use of strong opioids over months or years. Both therapeutic and chronic use of opioids can compromise the function of the Immune System . Opioids decrease the proliferation of Macrophage progenitor cells and Lymphocyte s, and affect cell differentiation (Roy & Loh, 1996). Opioids may also inhibit Leukocyte migration. However the relevance of this in the context of pain relief is not known. Treating opioid adverse effects Most adverse effects can be managed successfully. (For more complete information see ''Oxford Textbook of Palliative Medicine'', 3rd ed. (Doyle D, Hanks G, Cherney I and Calman K, eds. Oxford University Press, 2004). and the online palliative care formulary available on Palliativedrugs.com .) ''Nausea:'' tolerance occurs within 7–10 days, during which antiemetics (e.g. low dose haloperidol 1.5–3mg once at night) are very effective. ''Vomiting:'' if this is due to gastric stasis (large volume vomiting, brief nausea relieved by vomiting, oesophageal reflux, epigastric fullness, early satiation) then this can be managed with a prokinetic (e.g. domperidone or metoclopramide 10mg every eight hours), but usually needs to be started by a non-oral route (e.g. subcutaneous for metoclopramide, rectally for domperidone). ''Drowsiness:'' tolerance usually develops over 5–7 days, but if troublesome, switching to an alternative opioid often helps. ''Constipation:'' this develops in 99% of patients on opioids and since tolerance to this problem does not develop, nearly all patients on opioids will need a laxative. Over 30 years experience in palliative care has shown that most opioid constipation can be successfully prevented: "Constipation ... is treated laxatives and stool-softeners " (Burton 2004, 277). According to Abse, "It is very important to watch out for constipation, which can be severe” and “can be a very considerable complication” (Abse 1982, 129) if it is ignored. ''Respiratory depression:'' Although this is the most serious adverse reaction associated with opioid use it usually is seen with the use of a single, intravenous dose in an opioid-naive patient. In patients taking opioids regularly for pain relief, tolerance to respiratory depression occurs rapidly, so that it is not a clinical problem. ''Reversing the effect of opioids:'' Opioid effects can be rapidly reversed with an opioid antagonist such as Naloxone or Naltrexone . These Competitive Antagonist s bind to the opioid receptors with higher affinity than agonists but do not activate the receptors. This displaces the agonist, attenuating and/or reversing the agonist effects. However, the Elimination Half-life of naloxone can be shorter than that of the opioid itself, so repeat dosing or continuous infusion may be required. In patients taking opioids regularly it is essential that the opioid is only partially reversed to avoid a severe and distressing reaction of waking in excruciating pain. This is achieved by not giving a full dose (e.g. naloxone 400 microg) but giving this in small doses (e.g. naloxone 40 microg) until the respiratory rate has improved. An infusion is then started to keep the reversal at that level, while maintaining pain relief. Dangerous opioids or dangerous prescribers? There are a number of paradoxical beliefs about opioids:
How safe are opioids? A world view Studies around the globe over the past 20 years have repeatedly shown opioids to be safe when they are used correctly. In the UK two studies have shown that double doses of bedtime morphine did not increase overnight deaths,Regnard C and Badger C. Opioids, sleep and the time of death. ''Palliative Medicine'', 1987; 1(2): 107–110. and that sedative dose increases were not associated with shortened survival (n=237).Sykes N. Thorns A. Sedative use in the last week of life and the implications for end-of-life decision making. ''Arch Int Med'' 2003: 163(3): 341–4. Another UK study showed that the respiratory rate was not changed by morphine given for breathlessness to patients with poor respiratory function (n=15).Boyd KJ. Kelly M. Oral morphine as symptomatic treatment of dyspnoea in patients with advanced cancer. ''Palliative Medicine''. 1997: 11(4): 277–81. In Australia, no link was found between doses of opioids, benzodiazepines or haloperidol and survival.Good PD, Ravenscroft PJ, Cavenagh J. Effects of opioids and sedatives on survival in an Australian inpatient palliative care population. ''Int Med J.'' 2005: 35(9): 512–7. In Taiwan, a study showed that giving morphine to treat breathlessness on admission and in the last 48 hours did not affect survival.Hu WY, Chiu TY, Cheng SY, Chen CY. Morphine for dyspnoea control in terminal cancer patients: is it appropriate in Taiwan? ''J Pain & Symp Manag.'' 2004: 28(4): 356–63. The survival of Japanse patients on high dose opioids and sedatives in the last 48 hours was the same as those not on such drugs.Morita T, Tsunoda J, Inoue S, Chihara S. Effects of high dose opioids and sedatives on survival in terminally ill cancer patients. ''J Pain & Symp Manag.'' 2001: 21(4): 282–9. In U.S. patients whose ventilators were being withdrawn, opioids did not speed death, while benzodiazepines resulted in longer survival (n=75).Chan JD et al. Narcotic and benzodiazepines use after withdrawal of life support: association with time of death? ''Chest.'' 2004: 126(1): 286–93. Morphine given to elderly patients in Switzerland for breathlessness showed no effect on respiratory function (n=9, randomised controlled trial).Mazzocato C, Buclin T, Rapin CH. The effects of morphine on dyspnoea and ventilatory function in elderly patients with advanced cancer: a randomized double-blind control trial. ''Annals of Oncology''. 1999: 10(12): 1511–4. Injections of morphine given subcutaneously to Canadian patients with restrictive respiratory failure did not change their respiratory rate, respiratory effort, arterial oxygen level, or end-tidal carbon dioxide levels.Bruera E, Macmillan K, Pither J, MacDonald RN. Effects of morphine on the dyspnoea of terminal cancer patients. ''J Pain & Symp Manag'', 1990: 5(6): 341–44. Even when opioids are given intravenously, respiratory depression is not seen.Bassam E, ''et al'' Respiratory function during parenteral opioid titration for cancer pain. ''Palliative Medicine'', 2007; 21: 81-86. Using opioids safely
The unsafe use of opioids: the overdose Opioids have a well defined acute Toxicity for Respiratory Depression , so a single but large enough dose of an opioid can casue life-threatening respiratory depression. Fortunately, the safety margin for most opioids is very wide. Usually respiratory depression is not a problem in pain or palliative care medicine. The reason for this is not the level of dose, but the speed of titration. Good practice is to titrate the dose to the individual in 25-50% steps at 2-3 day intervals, until pain control is achieved with the minimal of adverse effects. In contrast, giving a large dose to a person who has previously taken no opioids is likely to casue problems. Double effect—a myth with a double life? The principle of Double Effect is not used in palliative care. Doctors are not faced with the dilemma of giving a potentially lethal drug dose to a distressed patient.George R, Regnard C. Lethal opioids or dangerous prescribers? ''Palliative Medicine'', 2007; 21: 77-80. A palliative care doctor gives repeated, small doses of one or more drugs, each titrated to an individual until the symptoms are eased, while doing everything possible to avoid toxicity. Doctors who give 30–60 times the required dose of morphine or diamorphine, usually as a single intravenous dose, are acting either negligently or maliciously. Since drug records should exist for opioids, there is a clear audit trail to follow if a subsequent investigation is required. With exceptions such as Shipman, UK doctors are very cautious about shortening life.Seale C. Characteristics of end-of-life decisions: survey of UK medical practitioners. Palliative Medicine 2006; 20(7): 653–9 The persistent belief that opioids and sedatives shorten life or hasten death stems from the experiences of bad practice in the use of the drugs. Evidence in the last 20 years has shown that opioids and sedatives are safe when following palliative care protocols. Clinicians who believe otherwise should be challenged to provide robust clinical evidence to support their view. Strong opioids such as morphine are inherently safe when used correctly, but they are powerful drugs with the potential for harm. There is a parallel here with power tools which are inherently safe unless they are used in a negligent or malicious way. Why blame the tool—morphine—and ignore bad prescribers? Other concerns about opioids Tolerance, dependence, addiction and abuse These issues cause doctors and patients many concerns, and are the most common reasons for inadequate use of analgesia in patients with severe pain. Putting these issues into the context of analgesia is important. '' Tolerance '' is the tendency of the body to adapt to the presence of opioids and is a common reaction to any chemical, including caffeine. Tolerance is more pronounced for some effects than for others; thus, opioids demonstrate ''selective tolerance:''
'' Dependence '' is the tendency of the body to manifest a characteristic and unpleasant '' Withdrawal Syndrome '' if regular doses of opioids are abruptly discontinued after tolerance has developed. This is also common for many chemicals, including coffee. For opioids the withdrawal syndrome generally consists of severe Dysphoria , anxiety, eye tearing, a Runny Nose , Goose Bumps , sweating, nausea, vomiting, cramps and deep pains are common. For patients taking opioids for pain relief, this can occur in some (but not all), but it is not a clinical problem, since most can rapidly reduce their opioids over 1–2 weeks without precipitating a physical withdrawal syndrome.Oxford Textbook of Palliative Medicine, 3rd ed. (Doyle D, Hanks G, Cherney I and Calman K, eds. Oxford University Press, 2004) '' Addiction '' is a psychological craving for certain effects of opioids (such as the euphoria that many people experience when the drugs are taken in sufficiently large doses) that drives the user to take the drug despite adverse and maladaptive consequences. Dependency and the unpleasantness of withdrawal can work to maintain addiction, although they do not cause it. This occurs only in specific social circumstances for an individual. Consequently, addiction is common in people taking opioids recreationally, but it is very rare in patients taking opioids for pain relief.''Oxford Textbook of Palliative Medicine'', 3rd ed. (Doyle D, Hanks G, Cherney I and Calman K, eds. Oxford University Press, 2004). '' Abuse '' is the misuse of opioids in the context of addiction. =Prevention of tolerance There is evidence that the mechanism by which opioid tolerance develops is different than the mechanism by which opioids inhibit pain. The significance of this is that the effects of opioids could, potentially, be realized while, at the same time, addiction and tolerance could be delayed or prevented and (possibly) even reversed. {Link without Title} {Link without Title} =Drug abuse issues In opioid addiction (rarely seen in patients taking opioids for pain relief), the speed and severity of withdrawal depends on the half-life of the opioid—heroin withdrawal occurs more quickly and is more severe than methadone withdrawal, but methadone withdrawal takes longer. The acute withdrawal phase is often followed by a protracted phase of depression and insomnia that can last for months. Withdrawal symptoms can be minimized by slowly tapering the dose over days or weeks, sometimes after switching to a long-acting opioid such as methadone. The symptoms of opioid withdrawal can also be treated with other medications, but with low efficacy. Hermann D, Klages E, Welzel H, Mann K, Croissant B. Low efficacy of non-opioid drugs in opioid withdrawal symptoms. Addict Biol. 2005 Jun;10(2):165-9. PMID: 16191669 Occasionally, people who are addicted to opioids on the street develop a painful condition which requires strong opioids. Carers are often very reluctant to give these patients analgesia, fearing it will make their addiction worse. Paradoxically, increasing experience of caring for such patients in palliative care has shown that they can be managed in the same way as any other patient with regular administration of opioids, plus extra doses for breakthrough medication. It seems that, because the social context is fundamentally different to the one when they were abusing their drugs, they do not run the risk of addiction. Indeed, if the cause of the pain settles, they can reduce their opioids without problem. EXAMPLES OF OPIOIDS Endogenous opioids Opioid- Peptide s that are produced in the body:
Dynorphin acts through κ-opioid receptors, and is widely distributed in the CNS, including in the Spinal Cord and Hypothalamus , including in particular the Arcuate Nucleus and in both Oxytocin and Vasopressin neurons in the Supraoptic Nucleus . Enkephalin is widely distributed in the CNS;[met -enkephalin is a product of the proenkephalin gene, and acts through μ and δ-opioid receptors. {Link without Title} -enkephalin, also a product of the proenkephalin gene, acts through δ-opioid receptors. Nociceptin , formerly known as orphanin FQ, is an opioid-related peptide, but it does not act at the classic opioid receptors and actions are not antagonised by the opioid antagonist naloxone. Nociceptin is a potent anti-analgesic. Noiceptin is widely distributed in the CNS; it is found in many regions of the hypothalamus, brainstem, forebrain, as well as in the ventral and dorsal horns of the spinal cord. Nociceptin acts at the NOP1 receptor, formerly known as ORL-1. The receptor is also widely distributed in the brain, including in the cortex, anterior olfactory nucleus, lateral septum, hypothalamus, hippocampus, Amygdala , central gray, pontine nuclei, interpeduncular nucleus, substantia nigra, raphe complex, locus coeruleus, and spinal cord. Endomorphin acts through μ-opioid receptors, and is more potent than other endogenous opioids at these receptors. β-endorphin is expressed in Pro-opiomelanocortin (POMC) cells in the Arcuate Nucleus and in a small population of neurons in the brainstem, and acts through μ-opioid receptors. β-endorphin has many effects, including on sexual behavior and appetite. β-endorphin is also secreted into the circulation from pituitary Corticotropes and Melanotropes . α-neoendorphin is also expressed in POMC cells in the arcuate nucleus Opium alkaloids Phenanthrene s naturally occurring in Opium : Preparations of mixed opium alkaloids, including Papaveretum , are still occasionally used. Semisynthetic derivatives
Synthetic opioids Anilidopiperidine s Phenylpiperidine s
Diphenylpropylamine derivatives
Benzomorphane derivatives Oripavine derivatives Morphinan derivatives Others Opioid antagonists SEE ALSO REFERENCES EXTERNAL LINKS
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