OPIOID ANALGESICS (ANALGESICS – ANODYNES) Pain nDefinition: „subjective unpleasant sensory or emotional experience accompanied by real or potential damage of tissues, with motoric and vegetative responses “ A) by duration B) according to pathophysiology Pain – types and classification A) According to length of experience 1) acute: sign of and disease, danger or damage to organism... 2) chronic: more than 3 months / unusually long for a given disease or disorder Pain – types and classification A) According to length of experience 1)acute: physiological sensory perception, -tissue damage, -mobilizes defensive forces of the organism in order to remove the inducing cause of the pain 2) chronic: pathological, pain may persists even after the removal of the causes → difficult to determine whether the pain arose as a result of persistent pathological activity in the nerve endings in the periphery, or is the source of the CNS Pain – types and classification B) According to pathophysiology 1) nociceptive – irritation of nociceptors Therapy: „analgesic ladder“ according WHO (see below; not used for aggressive procedure in the treatment for cancer or breakthrough pain) 2) neurological and neuropathic pain Therapy: antidepressants and anticonvulsants (in combination with opioids or some muscule relaxants; neuroprotective vitamins – thiamine; antimigraine drugs from the group of the so-called triptans; antipsychotics = neuroleptics) Pain – types and classification B) According to pathophysiology 3) psychogenic pain somatization, hypochondric and somatoform disorder Therapy: psychopharmac drugs (antidepressants – TCA, SSRI, anxiolytics, antipsychotics) Pain – types and classification nneuralgia sharp, paroxysmal pain, affects peripheral or cranial nerves (often the trigeminus, facialis) → after traumatological damage, compression, viral infects (herpetic), metabolic (DM) npain in the chronic compression of peripheral nerves and nerve roots hernia of the intervertebral discs, compression of the nerve in the spinal cord → pain + paresthesia, pain acquires a hot character Special types of pain nischemic pain due to disorders of blood circulation in the myocardium, smooth or skeletal muscle nmigraine migraine is characterized by attacks of pulsating, mostly unilateral headache lasting typically 4-72 hours with nausea, possible vomiting, photofobia and phonofobia, suffering from 12% of the adult population Special types of pain nphantom pain surgically or traumatically removed parts of the human body, most commonly the lower limb or other parts of the body (ablation of the breast, as well as after the removal of the visceral organs - the colon); apply pathophysiological influences peripheral, central and psychogenic; nbreakthrough pain sudden, transient, mostly short-term worsening of pain in patients who have well-controlled baseline pain; usually in patients treated with opioids for cancer diagnosis; typically in progression of cancer Special types of pain ndelivery pain - belongs to the strongest pain reliever, nevertheless, that before the birth are rising thresholds for somatic and visceral pain - the tissue is developed by excessive pressure, they are strongly being pushed and lacerations occur - tissues are under influence of bradykinin, H+, K+, histamine and serotonin - induction of stress → ↑ cortisol, epinephrine, norepinephrine, dopamine → somatic and psychological reactions Special types of pain ONCOLOGICAL PAIN SOMATIC MANIFESTATIONS sharp or dull pain Inflammatory response colic pain neuralgia EMOTIONAL MANIFESTATIONS anxiety depression SOCIO-ECONOMIC IMPACT personality changes care of the security of the family the breakdown of the family loss of friends EXISTENTIAL CONCERNS concerns about the course of the disease general uncertainty the fear of death VAS: Visual analogue scale Diagnostics of Pain NO PAIN THE WORST PAIN YOU CAN IMAGINE Process of pain perception algognostic component algothymic component Pain – causes and mechanism Mediators of pain (act on the nociceptors = pain receptors) „algogenic substances“ bradykinin + ↑PGE (mediators of inflammation), increase sensitivity of nociceptors histamine acetylcholine substance P (pain) tissue damage  production of prostaglandines and other substances  effects on the free nerve endings  transduction of signal up to the brain neurons  PAIN Endogenous pain suppressing (analgesic) substances: endorphins enkephalins dynorphins binding to α2 and NMDA receptors Pain – causes and mechanism Pain transduction – 3 neuron`s tract tractus spinothalamicus (spinothalamic tract) vs. tractus spinoreticulothalamicus (spinoreticulothalamic tract) MAIN PAIN PATHWAYS the tracks leading from the spinal cord (spinal ganglia) to specific areas of the brain (finally to the cerebral cortex) information about pain is received and processed Pain transduction – 3 neuron`s tract → spinothalamic tract – 3 neuron`s phylogenetically younger pathway – sharp, well localized pain → spinoretikulothalamic tract – phylogenetically older polysynaptic system, impulses are transmitted to the higher centres through short axonal pathways – dull, poorly localized pain nvegetative response: blood pressure change, tachypnea, mydriasis, diaphoresis, increased muscle tone,... Analgesics – anodynes (opioids) Non-opioid analgesics (analgesics – antipyretics  NSAIDs) Local anaesthetics General anaesthetics Adjuvant therapy (antidepressants, neuroleptics - antipsychotics, antiepileptics - anticonvulsants, antimigrenics, central/peripheral myorelaxants, corticoids, bisphosphonates, caffeine…) Pharmacological modulation of pain analgesics – anodynes (opioids) Analgesics – suppress perception of pain (increase the pain threshold) selectively without influencing perception of other stimuli non-opioid analgesics act on spinal and supraspinal level, cause effects on somatic and visceral pain, strong effects on consciousness, act substantially more strongly than non-opioid analgesics mostly peripheral effects (some have central effects!), effects on inflammation, weaker effects in general, no effects on visceral pain, no addiction Pharmacological modulation of pain Analgesics - anodynes Opiates substances similar structurally to morphine with analgesic effect (natural origin, currently produced synthetically) Opioids + synthetic, semisynthetic and endogenous opioid peptides + exogenous opioid analgesics blocking transmission of pain signals between cells of the CNS (in the spinal cord, brain), as well as endogenous opioids: endorphins, enkephalins, dynorphins → binding to opioid receptors (agonists) Opioid receptors - μ κ δ (σ) • G-protein coupled •the interaction of the opioid with receptor → G- protein inhibition → reduction of neurotransmitter release + inhibition of neuronal activity •adenylylcyclase inhibition, facilitation of K+ channels opening postsynaptically, inhibition of Ca2+ channels opening presynaptically n  n κ n δ n(σ) nμ – supraspinal analgesia, euphoria, sedation, miosis, breath depression, addiction, GIT effects nκ – spinal + peripheral analgesia, sedation, dysphoria, miosis, GIT effects, (somatic addiction) nδ – spinal analgesia, breath depression, inhibition of GIT motility n[σ – dysphoric effect, psychotomimetic effect (hallucinations, perception disturbances), anxiety] Opioid receptors - μ κ δ (σ) Opioid receptors - μ κ δ (σ) FOR ANALGESIC EFFECT IS CRUCIAL ESPECIALLY ACTIVATION OF RECEPTORS: μ – supraspinal analgesia κ – spinal + peripheral analgesia Opioid receptors - μ κ δ (σ) FOR ANALGESIC EFFECT IS CRUCIAL ESPECIALLY ACTIVATION OF RECEPTORS: FOR ADDICTION IS CRUCIAL ESPECIALLY ACTIVATION OF RECEPTORS: μ – supraspinal analgesia, euphoria κ – spinal + peripheral analgesia Pharmacological influence on opioid receptors Atypical opioids agonists (strongly effective, moderate/weakly effective) partial agonists – dualists mixed agonists - antagonists antagonists Pharmacological effects of analgesics - anodynes CENTRAL: analgesic suppression of respiratory center sedation (+-) suppression of anxiety euphoria/dysphoria antitussive effect nausea and vomiting  tendency to convulsions/cramps miosis secretion of ADH,  GnRH, corticotropine, FSH, LH, ACTH, cortisol, testosterone) TOLERANCE !!! (to all effects of opioids except constipation and miosis!) ADDICTION !!! Pharmacological effects of analgesics - anodynes PERIPHERAL: •decrease intestinal motility, slowdown propulsion of GIT content •increase muscle tone of GIT and urinary bladder •increase sphincter tone of gall bladder and urinary bladder •constriction of pyloric sphincter, delayed gastric emptying •vasodilation, orthostatic hypotension •histaminoliberation •inhibition of ciliated epithelium •urological tract – increase tone of renal pelvis, ureter, m. detrusor and sphincter of bladder…urine retention, especially in post-operative conditions •uterus - ↓ tone and motility, may prolong labor Pharmacological effects of analgesics - anodynes ABSORPTION DISTRIBUTION parenteral oral („first pass effect“ !!!) perrectal transdermal sublingual transmucous (nasal) parenchymatous organs muscles adipose tissue (lipophilic drugs ➙ e.g. fentanyl) pass well across BBB ➙ brain (fentanyl, heroin,..) Can cross placental barrier !!! Pharmacokinetics of analgesics - anodynes BIOTRANSFORMATION EXCRETION primarily in liver polar metabolites • inactive metabolites • active metabolites (codeine, tramadol, morphine…) • kidneys - urine • liver - bile Pharmacokinetics of analgesics - anodynes Opioid agonists morphine • 10 % of opium content, together with codeine, thebaine + other phenanthrene alkaloids • isolated in 1803 (Sertürner) • high affinity to  receptors – selective µ agonism Opioid agonists morphine Ø see above effects Ø application routes: Ø orally (also p.o. with sustained release) Ø parenterally (i.v., i.m., s.c., epidural,… ) Ø perrectally Indications: chronic cancer pain, pain after surgery, injuries, (pain during acute myocardial infarction → today, given preference to other opioids) Opioid agonists Opioid agonists Other strong opioid analgesics methadone • less sedation and euphoria than in morphine • ↑ bioavailibility after oral administration, ↑t ½ • acts on opioid + NMDA receptors • Use: addiction treatment (heroin) ➙ 2 benefits ➙ change from injection application to oral administration ➙ ↑t ½ decreases plasmatic fluctuation of methadone ➙ less withdrawal symptoms Opioid agonists Other strong opioid analgesics heroin (= diacetylmorphine) • not used in clinical medicine (in Czech Republic) (but in Great Britain can be therapeutically used!) • causes severe addiction; abused! • heroin belongs to the most health and personality devastating substance!!! Opioid agonists fentanyl, sufentanil, remifentanil,… • pass well across HEB (↑ concentrations in CNS) • strong, short analgesia (fentanyl 100 x more potent than morphine, sufentanil 1000 x more potent than morphine) • strong respiratory depression!, ↓ emetogenic potency, CAVE ➙ can cause muscle rigidity • risk of serotonin syndrome in combination with 5-HTergic drugs Other strong opioid analgesics Opioid agonists fentanyl, sufentanil, remifentanil,… • Indications, use: • in anaesthesiology ➙ neuroleptanalgesia (= neuroleptic (AP) + opioid) ➙ analgosedation (e.g. opioid + BZD) • therapy of strong pain – acute myocardial infarction, cancer pain,… • fentanyl in TTS (↑ duration of action – can be used in chronic cancer pain), transmucous (can be used in breakthrough pain) Other strong opioid analgesics Opioid agonists piritramid • less respiratory depression than morphine • less emetogenic potency • usually well tolerated parenteral administration • Use: therapy of acute strong pain, e.g. after surgery (PCA), acute myocardial infarction, pain after injuries,… Others: oxycodone, hydromorfone (not registered in Czech Rep.), oxymorphone (not registered in Czech Rep.) CAVE: all strong opioids are prescribed to forms with blue band („opiate forms“), very strict accounted and subjected to the rules for handling with narcotics and psychotropic drugs and their precursors!!! Other strong opioid analgesics Opioid agonists Other strong opioid analgesics pethidine (=meperidine) •↓suppression of respiratory center than morphine •↓analgesic potency than morphine (5-10 x weaker) •metabolite norpethidine is proconvulsive and causes hallucinations •administration orally and parenterally Indications: cancer pain, pain after injuries, pain during acute myocardial infarction, pain after surgery, premedication before general anaesthesia…today not often used (high risk of abuse, hallucinations!) Opioid agonists codeine • 10 % mtb. to morphine • antitussive effect in subanalg. doses • analgesic effect in combinations (paracetamol, ASA) analgesic potency: codeine 50mg ~ ASA 1g •  risk of addiction than strong opioids • CAVE ↑ risk of addiction of combined (compositive) analgesics • causes obstipation • not used in children!!! Opioid agonists (moderate and weak potent) Opioid agonists dihydrocodeine • suitable in pains combined with cough (this co-incidency is not necessary for dihydrocodeine indication) • in Czech Rep. dihydrocodeine in sustained release drug form (effect 12 h) ➙ indication for chronic moderate and strong pain Side effects: obstipation, ↑liver tests, histaminoliberation Opioid agonists (moderate and weak potent) Opioid agonists CAVE: codeine and dihydrocodeine are prescribed to normal forms - without blue band! Partial agonists + mixed agonists - antagonists • lower affinity to μ receptors, high affinity to κ rec., • respectively κ-agonists - μ-antagonists or partial μ receptor agonists (buprenorphine) • less potential for addiction, but exists! • lower analgesic effect than full agonists • less side effects than full agonists Partial agonists Mixed agonists - antagonists buprenorphine • partial μ rcp. agonist • ↓tolerance in comparism with other opioids • ↓abuse potential, obstipation and other GIT effects •↑ „first pass effect“ ! Do not administer orally!!! • Use: 1) strong chronic pain (TTS!) 2)substitution therapy of opioid (heroin) addiction ➙ combined with opioid antagonist naloxone in one drug form (sublingual) ➙ in injection application naloxone antagonizes effects of buprenorphine (in sublingual administration naloxone does not act!) Partial agonists Mixed agonists - antagonists Partial agonists + mixed agonists - antagonists Partial agonists Mixed agonists - antagonists Partial agonists + mixed agonists – antagonists – other representatives •mixed agonists – antagonists •usually μ-antagonists and κ-agonists (event. also δ-agonists) •possibility of σ-receptor activation → psychotomimetic and hallucinogenic effects) •analgesic effects are weaker than full agonists •today minimal use •pentazocin, butorfanol – in Czech Rep. not registered nalbuphine • for short-term therapy of moderate and strong pain • unsuitable for long-term therapy • parenteral administration (i.v., i.m., s.c.) • causes respiratory depression comparable to morphine, but suppression of respiratory center has drug ceiling effect • Use: perioperative pain, suppression of pain in obstetrics (BE AWARE: in newborns risk of breathing depression, bradycardia, cyanosis and hypotension → newborn`s monitoring necessary!) Partial agonists + mixed agonists – antagonists – other representatives Partial agonists Mixed agonists - antagonists Atypical opioids tramadol • low affinity to μ receptors + norepinephrine and serotonin reuptake inhibition (= atypical mechanism of action, similar to some antidepressants from SSRI group; effect of tramadol can not be fully antagonized by opioid antagonists) • approximately 1/6 – 1/10 of morphine analgesic potency • very suitable combination with paracetamol • less side effects (minimal respiratory depression) • risk of serotonin syndrome • in Czech Rep. very often prescribed analgesic, prescription to normal forms without blue band; more drug forms • RISK OF ADDICTION!!! Use: therapy of moderate and strong pain (acute and chronic) Atypical opioids tapentadol • dual mechanism of action - μ agonist + NRI (+ σ agonist) NEW GROUP – MOR-NRI (μ receptor agonism – noradrenaline reuptake inhibitor) • more effective than tramadol, analgesia comparable with oxycodone, but less adverse effects • suitable for the treatment of acute (but also chronic pain – e.g. vertebrogenic; also effective in diabetic neuropathy - neuropathic pain!!!) • relatively few adverse effects (compared to classical strong opioids, e.g. oxycodone) • p.o. administration (also tbl. with sustained release) Atypical opioids Atypical opioids CAVE: tapentadol is prescribed to forms with blue band („opiate forms“), very strict accounted and subjected to the rules for handling with narcotics and psychotropic drugs and their precursors!!! Antagonists of opioid receptors naloxone, naltrexone Indications: treatment of opioid intoxication, treatment of respiratory depression induced by opioids, addiction diagnostics (withdrawal symptoms) TRIAD: coma, respiratory depression, miosis Opioid antagonists Antagonist / partial agonist nalmefen antagonist ,δ, partial Ƙ agonist „controlled drinking“ Opioid antagonist/partial agonist Opioid-induced side effects nrespiratory depression (suppression of breathing) nnausea and vomiting nsedation, inhibition of cognitive functions nconstipation (solution = oxycodone + naloxone) nADDICTION nbe carefull in pro-convulsive states! (e.g. epilepsy – proconvulsive action – decrease of the threshold for seizures) n intracranial pressure Intoxication by opioid agonists nausea, „flush“, tinnitus apathy, sedation, sleep, miosis superficial breathing cyanotic, cold skin, tachycardia asphyxia TRIAD: coma, respiratory depression, miosis Treatment: naloxone i.v. ventilation, vital functions, parenteral liquids in unconsciousness > Withdrawal symptoms „craving“ („drogenhunger“), „craving“ for the another dose (psychic addiction arises easiest to heroin, oncology patients treated with opioids ➙ < 1% of patients) unrest, depression anxiety, weakness, nervousness, mydriasis lacrimation, ↑ nose secretion, frisson (goosebumps), ↑ perspiration, pain, stenocardia occur approximately after 3-4 weeks of opioid administration Rules of pain therapy management nChoice and course of analgetic therapy depends on intensity and character of pain described by the patient – individual dosing – titration may take weeks in CHP nAcute pain – course - from up going down – start with strong medication (opioid), parenteral administration, fast onset (eg. pain in AIM, renal or biliar colic) nIn chronic pain – course – from down going up – non-invasive preparations (p.o., TTS), slower release according to a time plan nIn some types of fluctuating chronic pain it may be necessary to give patient rescue medication in case of breakthrough pain nCombination of non-opioid and opioid analgesics has additive effect nBenefits of analgesic therapy should exceed its side effects. nAE must be prevented rather than treated when they appear – eg. antiemetics, diet, laxatives nThere is not a maximal dose of opioid – (in case of full agonists and cancer pain) nRotation of opioids Rules of pain therapy management Rotation of opioids nSwitch in case of AE nSometimes even in equianalgesic dose increase of effect General rules of pain pharmacotherapy management nWHO's pain relief ladder ºStep 1 (VAS 0-4) nnon-opioid analgesics ± adjuvant treatment ºStep 2 (VAS 4-7) npain persists, intensifies, no change in the objective finding nweak/moderate opioid analgesics ± non-opioid analgesics ± adjuvant treatment ºStep 3 (VAS 7-10) npain persists, intensifies, there is no indication for another treatment nstrong opioid analgesics ± non-opioid analgesics ± adjuvant treatment ± weak/moderate opioid analgesics Other indications of opioids na n titussive effect ncan be induced by codeine and dextromethorphan in dry non- productive cough nconstipative effect ncan be induced by loperamide and diphenoxylate in functional diarrhea np r e m e d i c a t i o n before anaesthesia and surgery under general anaesthesia nleads to calm the patient and based on the synergism of drugs reduces the total dose of narcotics (thereby increasing the safety of anaesthesia) nparticularly fentanyl and its derivatives are used ncombination of opioid analgesic with neuroleptic (fentanyl + droperidol) within neuroleptanalgesia nr e p l a c e m e n t (substitution) therapy of addiction to heroin or other opioids – methadone, buprenorphine