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OPIOID ANALGESICS PowerPoint Presentation

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Description : Check out this medical presentation on Pharmacology, which is titled "Opioid Analgesics", to know about Opioid Analgesics, drugs, relieving pain due to multiple causes (analgesics).

Tags : Pharmacology, Opioid Analgesics, drugs, relieving pain, analgesics

Published on : Jul 18, 2021 | Views : 3285 | Downloads : 14

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Medical University of Sofia, Faculty of Medicine Department of Pharmacology and Toxicology OPIOID ANALGESICS Assoc. Prof. Ivan Lambev E-mail: itlambev@mail.bg
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Pain is the most common symptom for which patients see a doctor. Different types of drugs are used for treatment of pain. In general, they include: 1. Drugs, relieving pain due to multiple causes (analgesics) Ø narcotic analgesics (morphine, fentanyl, etc): act chiefly in the CNS Ø non-narcotic analgesics (paracetamol, metamizole): act chiefly peripherally
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2. Drugs relieving pain due to a single cause or specific pain syndrome only They are not classified as analgesics: e.g. naratriptan (migraine), carbamazepine (neuralgias), glyceryl trinitrate (angina pectoris), adrenal steroids (inflammatory pain), butylscopolamine (spasm of visceral smooth muscles), baclofen (spasm of striated muscles), etc.
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3. Adjuvant drugs (anxiolytics, neuroleptics, antidepressants) may modify the perception of pain and remove the concomitants of pain such as anxiety, fear, depression. Placebo gives relief in 3%. 4. Anaesthetics (general and local) are used during surgical operations, some diagnostic, and other painful procedures.
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Nociception is a consequence of tissue injury (trauma, inflammation). It causes the release of chemical mediators (ACh, PGE, NA, 5-HT, glutamate, bradykinin, endogenous opioids, adenosine). They have neuronal or non-neuronal origin. These mediators activate nociceptors. Nociceptors are pain-receptors. Nociceptors transmit information by thin myelin (A-delta) and non-myelin (C) fibers to the spinal cord and brain.
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Pain perception has a complex mechanism. It is a result of nociceptive impulses reaching the brain (thalamus, cortex), plus impulses from other peripheral receptors, e.g. heat and mechanoceptors, whose threshold of response is reduced by the same chemical mediators. These are processed in the brain whence modulated inhibitory impulses pass down to regulate the continuing afferent input. But pain can occur without nociception (e.g. some neuralgias). Pain is a psychological state, though most types of pain have a physical cause.
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MAIN TYPES OF PAIN Acute pain (defined as < 3 months duration) transmitted principally by fast conducting myelin A-delta fibers. It has major nociceptive input (physical trauma, pleurisy, myocardial infarction, perforated peptic ulcer). The narcotic (opioid) and sometimes non-narcotic analgesics are used for treatment of acute pain.
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Chronic pain (defined as > 3 months duration) is transmitted principally by slow conducting non-myelinated C fibers. It is better regarded as a syndrome rather than a symptom. It is depressing to the patient who sees no prospect for relieving the suffering. Analgesics alone are often insufficient and adjuvant drugs (antidepressants or neuroleptics) as well as non-drug therapy (including psychotherapy) have increasing importance.
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Neuropathic pain follows damage of the nervous system. Acute pain without nociceptive (afferent) input (e.g. some neuralgias) is less susceptible to analgesics. The suitable drugs are some antidepressants and carbamazepine. Transient pain is provoked by activation of nociceptors in the skin and other tissues in the absence of tissue damage. It protects humans from physical damage coming from the environment or excessive stressing of the tissue. It is a part of normal life and does not need treatment.
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HISTORY Opium is the dried juice of the seed head of poppy. It was used in prehistorical times (e.g. in Egypt, Ebers’Papyrus – XVI BC) as an analgesic, tranquillizer, antitussive drug, and for treating diarrhoea. The principal active ingredient in crude opium – morphine, was isolated in 1806 from Frederic Sertűrner, who tested pure drug on himself and three young men. He observed that morphine caused cerebral depression and relieved toothache. Gay Lussac named this drug, which was the first discovered alkaloid, after Morpheus (the son of Somnus) – morphine.
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Poppy
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Prof. Gay Lussac (1778–1850) Morpheus and Iris
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Opium contains two groups of alkaloids: with phenantrene structure (morphine, codeine, thebaine) with isochinoline structure (papaverine, noscapine). Morphine and codeine are narcotic analgesics; papaverine is a vasodilator; noscapine is an antitussive agent which is suspected of genotoxicity. Opium contains ≈10% morphine.
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Effects are mediated via opioid receptors m (mu): mediate analgesia at the supraspinal level d (delta): analgesia in the periphery k (kappa): analgesia at the spinal level ORL1 (opioid receptor like 1): dependence Mechanism of action of opioid analgesics
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There are endogenous analgesic substances with peptide structure and morphine-like action. They are called endogenous peptides and were discovered during the investigation of the mechanism of analgesic action of morphine.
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Endogenous opioid peptides are: a) enkephalins activate μ and δ-receptors; b) endorphins activate μ, κ and δ-receptors; c) dynorphins activate μ, κ and δ-receptors. d) nociceptin – ORL1 (tolerance) Opioid peptides act in CNS as: - neurotransmitters - modulators of response (usually inhibitory)
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The main effects of morphine are: on the CNS Depression, leading to analgesia, respiratory depression (decrease in sensitivity of the respiratory centre to PCO2), depression of cough reflex, sleep) Excitation, leading to vomiting, miosis (pupil constriction), convulsions (very rare) Changes of mood – euphoria (sense of well-being) or dysphoria. Tolerance and dependence (psychological and physical)
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Smooth muscle stimulation Gastrointestinal muscle spasm (with constipation) and biliary tract spasm Bronchospasm Retentio urinae Cardiovascular system Dilation of resistance and capacitance vessels Other effects Sweating, histamine release, pruritus, piloerection, antidiuretic effect
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Phenomenon of Straub Urine from patients intoxicated with opioids 1 ml/i.p.
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Tolerance and dependence Tolerance – it is increasing of the dose of a drug required to produce the same effect. It occurs rapidly with opioids (with morphine 12–24 hours, e.g. the hot plate test – in mice, after 3 days the dose of morphine required for analgesia increases 5-fold). Important in drug addiction – may need to increase dose 50-fold.
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Tolerance is not shown equally on all effects. Tolerance extends to: analgesia euphoria respiratory depression To much lesser extent on: constipation pupil constriction This is why constipation can be such a big problem with opioids.
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Why does tolerance occur? There are several potential reasons: - Increased metabolism of the drug - Decreased receptor affinity
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DEPENDENCE Takes two forms : physical psychological Physical dependence – problems include withdrawal syndrome (addiction): - Irritability - Weight loss - Shakes - Sweating - Piloerection “cold turkey” - Effects last off in 8–10 days
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Psychological dependence Problems are: - Desire for the drug - Want to experience the “rush” – positive - Don’t want the withdrawal – negative - Some opioids, e.g. codeine & pentazocine, are much less likely to cause dependence
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Principal uses of morphine and other opioids Relief of moderate to severe acute pain (or chronic pain often in terminal illness) Brief relief of anxiety in serious and frightening diseases accompanied by pain (e.g. traumas but without commotio) Relief of dyspnoe in acute left ventricular failure, and in terminal cases Premedication in surgery Treating of dry cough (usually codeine, dextromethorphan).
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Strong analgesics: Morphine Hydrochloride - 1% 1 ml (= 10 mg) i.m. with 1 mg Atropine - Morphine Sulfate 1 tab./12 h p.o. in humans Antitussive and week analgesic: - Codeine 10–20 mg/dose Alcaloids
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Semisynthetic derivative (opioid analogs) Morphine derivatives Ethylmorphine, Heroin Codeine derivatives Dextromethorphan (antitusive agent) Dihydrocodeine (Dicodin®): 1 tab./12 h Hydrocodone (Vicodin®) Oxycodone: p.o. Thebaine derivatives Buprenorphine, Etorphine
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ETORPHINE (strong μ/κ/δ-agonist) with remarkable very high potency, more than 1000–3000 times that of morphine. It is a semisynthetic derivative of thebaine. It is used im combination with Acepromazine (phenothiazine derivative) to immobilize large wild animals for trapping and research purposes, since the required dose, even for an elephant, is small enough to be incorporated into a dart or pellet.
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Targin® (oxycodone & naloxone) Suboxone® (buprenorphine & naloxone)
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Targin® (oxycodone & naloxone) Suboxone® (buprenorphine & naloxone)
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HEROIN (diamorphine – BAN, diacetylmorphine) Similar action to morphine More active than morphine More lipid soluble – crosses BBB faster to give greater rush Shorter duration of action than morphine
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PHENYLPIPERIDINES pethidine, fentanyl METHADONES methadone, dextropropoxyphene BENZOMORPHANS pentazocine TRAMADOL Synthetic derivatives
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Almost identical to morphine Tends to cause restlessness rather than sedation Antimuscarinic effects: dry mouth blurred vision Less antitussive Shorter duration of action (4-6 h) – preferred in labour PETHIDINE (Meperidine – USAN; Lydol® – Sopharma) Sol. 5% 2 ml (= 100 mg/2 ml) s.c./i.m.
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TRAMADOL Tramadol provides moderate pain relief. Because of its dual actions as a µ-agonist and monoamine transport inhibitor, it produces less respiratory depression for a given analgesic effect. Tramadol is a weak agonist at µ-receptors. Its major metabolites are more potent agonists at µ-receptors. Tramadol also inhibits monoamine transporters (principally NA and 5-HT) which is thought to produce analgesia synergistically with µ-agonism.
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FENTANYL >80 times more potent than morphine in analgesia Actions similar to morphine Main use is in anaesthesia, used in conjunction with droperidol, a neuroleptic, producing neuroleptanalgesia Durogesic® (Fentanyl): TTS/72 h
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Durogesic Durogesic TTS
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NEUROLEPTANALGESIA Fentanyl 100 mcg + Droperidol 5 mg i.m. Similar to Fentanyl: Alfentanil (NB: without “y”) Sufentanil (NB: without “y”)
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METHADONE Similar actions to morphine Longer duration of action (t1/2 37 h) Less problems with withdrawal Can be used to wean heroin and morphine addicts off the drug
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DEXTROPROPOXYPHENE (t1/2 5 h) is structurally similar to methadone and differs in that it is less analgesic and less dependence producing. Its weak μ/κ/δ-agonist analgesics usefulness approximates to that of codeine, but its duration of action is longer.
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Pentazocine – κ/δ-agonist/weak μ-antagonist
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Low efficacy for mild and moderate pain codeine, dihydrocodeine, dextropropoxiphene, oxycodone, pentazocine, tramadol High efficacy for severe pain alfentanil, buprenorphine, heroin, fentanyl, methadone, morphine, pethidine, sufentanil
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Durability: 7 days The recipe is stored in licensed pharmacies 10 years! Yellow Reception Form for Prescribing of Opioid Analgesics.
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OPIOID COMPETITIVE ANTAGONISTS Naloxone (μ, κ and δ-antagonist) Naltrexone (μ, κ and δ-antagonist) Nalorphine (Allylnormorphine) – μ-antagonist/κ-agonist)
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Opioid agonists which does not cross BBB Loperamide (Imodium®) and Racecadotril (Hidrasec®) These drugs stimulate mu- and delta-receptors, present in the small and large intestines. Activation of mu-receptors decreases peristaltic movements. Activation of delta- receptors contributes to their antisecretory effects. Although all opioids such as morphine and codeine have antidiarrhoeal effects, their CNS effects and dependence liability limit their usefulness. Loperamide directly stimulates mu- and delta-receptors. Racecadotril blocks enzyme encephalinase and increases local concentration of enkephalins in intestinal mucosa which then stimulate mu- and delta-receptors. This drug can be used orally from children under 5 years old (including babies), but Loperamide is contraindicated in children < 5 years old.
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mu- and delta-receptors. Racecadotril blocks enzyme encephalinase and increases local concentration of enkephalins in intestinal mucosa which then stimulate mu- and delta-receptors. This drug can be used orally from children under 5 years old (including babies), but Loperamide is contraindicated in children < 5 years old.