Chapter31. Opioid Analgesics & Antagonists

Transcription

1 Chapter31 Opioid Analgesics & Antagonists

2 Pain Acute pain: Identified event, resolves days weeks Usually nociceptive Chronic pain: Cause often not easily identified, multifactorial Indeterminate duration Nociceptive and / or neuropathic

3 CLASSIFICATION OF ANALGESIC DRUGS: 1. NASID 2. Opium alkaloid 3. Local anaesthetic and general anaesthetics 4. Other analgesic drugs (carbamazepine, phenytoin, rotundine)

4 Opium juice in the unripe seed pods of the opium poppy, papaver somniferum, god s own medicine

5 Abuse The history Shouldn t be forgotten Great incursive trade of opium into China in 18~19 th century.

6 History As long ago as 3400 B.C, the opium poppy was cultivated in lower Mesopotamia. 460 B.C. the Greek physician,hippocrates noted its effectiveness as a painkiller A.D ancient Indian describe the use of opium for diarrhea and sexual debility. In 1803, Friedrich Sertuerner of Germany, morphine named it after Morpheus, the god of dreams. a milestone. Heroin (diacetylmorphine) was first synthesized in In 1895, Bayer

7 1962, the analgesic site of morphine is at gray matter around third ventricle in CNS 1973 morphine receptors were be found, why? 1975 endogenous morphine like substances, enkephalin 1993, opioid receptors were be cloned Prof. Gang ZOU

8 subtypes of opioids receptors μ κ δ σ G protein coupled μ receptor: Analgesia, euphoria, respiratory depression and physiological dependence properties of the typical opioid receptor agonist κ receptor: Control spinal analgesia, sedation and miosis δ receptor: analgesia

9 Sensory neuron Neuron containing enkephalin Opioid receptor E:enkephalin; SP:substance P

10 Opioid receptors and mediated effects analgsia potency receptors μ δ κ brain +* + + spinal cord + +* +* Respiratory depression + ± miosis antitussives + sedative(euphoria) (anxiety) Gastointestinal(inhibition ) + ± Immunological depression + * Mainly effective site

11 Ingredient of opium 20 alkaloids Morphine, 10% Codeine, 0.5% papaverine(vasodilator) Thebaine %(produce convulsions

12 O H 2 O O H A 1 5 C B N C H 3 morphine

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14 morphine gastrointestinal(firstpass elimination ) Mucous membrane 鼻粘膜 of nose lung 肺 Injection 皮下 肌内注射 under skin or in muscle ( 吸收较好 ) absorption T 1/2 2.5~3.5h Milk or fetus 1/3 bind with plasma protein CNS Liberated morphine distribute in liver, lung, kidney,spleen, muscle Metabolism in liver kidney

15 pharmacological effects 1.Effects on CNS 1).analgesia Strong,high selective, with consciouses I. Raising the pain threshold, decreaseing pain perception of brain and increase the pain II. tolerance More effective against dull constant pain 2). Sedative 3). euphoria: An exaggerated feeling of physical and emotional well being, usually of psychologic origin.

16 4)Cough suppression 5)Nausea and Emesis: direct stimulate chemoreceptor trigger zone 6)Miosis: pinpoint pupil is the characteristic of all the addicts of opioids.

17 7)Respiratory depression: decrease the sensitivity of brain stem respiratory center to CO2. frequency of breathing, tidal volume

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20 2. Effects on muscle Smooth muscle, sphincter muscle Motility(rhythmic contraction and relaxation) may decrease but tone(persistent contraction)may increase Muscle tension of Urinary tract dysuresia muscle tension of bronchia Smooth muscle increased, asthma Tonicity of Sphincter muscle(biliary tract, urinary bladder,anus )

21 How to treat biliary colic and renal colic? morphine+atropin what lead by sphincter muscle of urinary bladder:dysuresia dysuresia

22 3. Cardiovascular system 1 No significant direct effects on the heart and on cardiac rhyth 2 Hypotension due to peripheral arterial and venous dilation 3 With increasing pressure of carbon dioxide, Cerebral vasodilation, increase in cerebral blood flow, and increase in intracranial pressure.

23 [theraputic application] 1. analgesia 1 Moderate to Severe constant pain; 2 Severe constant pain 3 Pain associated with Cancer and other terminal illness. Fixedinterval administrition is more effective in achieving pain relief than dosing on demand.

24 2. dyspnea caused by pulmonary edema associated with left ventricular failure 1reduce perception of shortness of breath 2reduce patient anxiety 3reduce cardiac preload(reduce venous tone) Left ventricular failure Pulmonary edema dyspnea Reduce anxiety Vasodilation morphine Lower the sensitivity of respiratory center to CO 2

25 3. in treatment of Diarrhea and causing constipation 4. Application in anesthesia sedative and analgesic effects

26 undesired effects 1. Respiratory depression, nausea, vomiting, constipation 2. Tolerance: large doses are given at short intervals

27 3. Physical dependence: Failure to continue take the drug results in a characteristic withdrawl include: rhinorrhea(nose running), lacrimation (tear),yawning, chills, gooseflesh, hyperventilation, vomiting, diarrhea, anxiety, and hostility endence: rh 4. Psychololgic dependence

28 withdrawl

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30 acute toxity Diagosis: known addict,, miosis( needle marks), respiratory depression, coma, less urine treatment:artificial breathing injecting naloxone

31 contraindications Combine with partial agonists Use during pregnancy Use in patients with impaired pulmonary Use in patients with head injuries, intracranial pressure

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33 codeine Moderate agonist 1/12 Analgesia effect of morphine; 1/4 preventing cough effect of morphine Less Sedative,euphoria and addictive than morphine; Less respiratory depression A useful antitussive

34 pethidine(dolandine, meperidine) 哌替啶, 度冷丁 Weaker analgesic effect than morphine; Analgesic duration is 2~4h; Used to relieve severe pain, but to treat cough and diarrhea

35 Not recommended... Meperidine: Poor oral absorption Short half life (2 3 hours) Nor meperidine is a toxic metabolite: Long half life (6 hours), not analgesic Psychotomimetic adverse effects, myoclonus, seizures renal insufficiency

36 fentanyl 芬太尼 Analgesic potency is 100 times than morphine, Short duration, about 30min; Combined with anesthetics,lower the dose of anesthetics

37 Methadone 美沙酮 Similar pharmacodynamic profile with morphine Slower development of tolenrence and dependence, milder withdrawl syndrome ; Detoxification of a heroin dependent addict

38 pentazocine 喷他佐辛 Mixed agonist antagonist(partial agonist) Agonism κ δreceptors, antagnism μreceptor,low addictive; Weaken analgesic effects of morphine and induce withdrawl of morphine addicts;

39 Not recommended Mixed agonist antagonists Pentazocine, butorphanol, nalbuphine, dezocine Compete with agonists withdrawal Analgesic ceiling effect High risk of psychotomimetic adverse effects with pentazocine, butorphanol

40 Tramadol 曲马多 Weak μreceptor agonist Inhibit NA and 5 HT reuptake Weak respiratory depression, little cardiovascular effects In Treatment of Moderate to serious pain Addiction after long time use Be useful in chronic neuropathic pain

41 Antagnist of opioid receptors naloxone 1. Affinity to all the 4opioid receptor: μ κ δ σ; 2. Without obvious effects if administerd alone 3. Addicts, withdrawl 4. Repeated injection in relieving severe respiratory depression 5. Tool in research.

42 naltrexone Similar with naloxone; Longer duration of action than naloxone