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Narcotic analgesics

Narcotic analgesics. Dr. Soha AlSayed. Narcotic analgesics. Definition: substance, whether endogenous or synthetic, that produces morphine-like effects that are blocked by antagonists such as naloxone . Receptors: Mu: all opioid effects and ADR except dysphoria

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Narcotic analgesics

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  1. Narcotic analgesics Dr. Soha AlSayed

  2. Narcotic analgesics • Definition: substance, whether endogenous or synthetic, that produces morphine-like effects that are blocked by antagonists such as naloxone. Receptors: Mu: all opioid effects and ADR except dysphoria Delta and kappa receptors MOA: - Decrease adenylcyclase & cAMP in brain - Inhibitcalcium channels in pre -synaptic neurons inhibit pain neurotransmitters release - Stimulate K-channels in post-synaptic neurons hyper-polarization

  3. Pharmacological actions • 1. Central effects (CNS): • I) Depressant effects a. Analgesia:without loss of consciousness by: • Inhibiting pain neurotransmitters release . • Modifyingemotional reactions to pain(Euphoria) b. Sedation: c. Respiration: Resp. depression d. Depress cough center: e. Hormones:decrease dopamine, CRH, ACTH, cortisol, LH, FSH & Testosterone f.Depress VMC: in large doses hypotension

  4. II) Stimulatory effects 1.Oculomotor nucleus pin-pointed pupil 2. CTZ: Nausea, vomiting 3. Pituitary hormones: Stimulates release of GH, prolactinand ADH 4. Cardiac center:bradycardia • 2. Peripheral effects: • 1. CVS: • A.Heart:bradycardia. (central and direct) • B. B.V:vasodilatation hypotension - Dilate cerebral BV ONLY when Resp depression CO2 accumulation  VD

  5. 2. Peripheral effects: • 2. GIT:Spasmogenic • Constipation through: 1. Decrease CNS perception of sensory stimuli for defecation. 2. Increase in tone in sphincters, decreasepropulsive contractions 3. Decrease in the GIT secretions. • 3. Urinary system: -Oliguria due to: increase ADH release + hypotension + increase tone of ureter and the vesical sphincter. • 4. Uterus & fetus:Is it a good analgesic forlabor pain? - Delay labor due to decrease pain sensation & spasm in uterine muscles -Pass placental barrier & BBB & suppress fetal respiration -Less conjugated in fetus higher blood level • 5. Immune system: Suppress immune system infection • 6.Skin: increase histamine release itching, urticaria,

  6. Effects of morphine

  7. Pharmacokinetics • A. Absorption: Well absorbed from all sites. In shock there is less absorption from S.C. and I.M. • B. Distribution: 1. Highly lipid soluble drugs e.g. Heroinare concentrated in highly perfused organs"brain" & accumulate in fat on prolonged administration 2. Crosses the placenta, less with tramadol & pethidine C. Metabolism: extensivefirst pass metabolism so oral dose is much higher than parenteral. - It is conjugated with Glucoronic Acid 2 metabolites: M3-G convulsions, M6-G (more active).

  8. D. Excretion: mainly renal Polar metabolites & small amount of free drug are excreted in urine. Renal impairment decrease excretion  toxicity. • Tolerance:after 2-3 w of continuous intake, need increase in dose up to 35 folds. 1. Marked tolerance tothe depressant effects 2. Notolerance toantagonistic or stimulant effectsEXCEPTemetic & antidiuretic. 3. There iscross tolerance to different opiates acting on same receptors.

  9. Dependence • Physical & psychogenic dependence • Sudden stopWithdrawal syndrome Adverse effects • 1. CNS:Respiratory depression +dependence • 2. GIT: Nausea, vomiting, constipation & colic. • 3. B.V: intracranial tension + Hypotension • 4. Muscles spasm: Urinary retention, increase biliary and renal colic & prolongation of labor. • 5. Histamine release: Itching, urticaria & bronchospasm.

  10. Therapeutic uses of Opioids • 1. TTT of pain • 2. Acute left ventricular failureand pulmonary edema. • 3. Anesthesia (adjuvant) • 4. Anti-diarrheal:diphenoxylate • 5. Cough:codeine.

  11. Contraindications & precautions • (Explain WHY for each one) • 1. bronchial asthma • 2. Head injury. • 3. Reduced blood volume (Induce hypotension) • 4. Myxoedema & Addison's disease(prolong and exacerbate response to opioids). • 5. Advanced hepatic & renal diseases. • 6. During pregnancy or delivery • 7. Prostate hypertrophy.8. Biliary & renal colic. • 9. Undiagnosed acute abdominal pain.

  12. Types of opioid analgesics • A. Pure agonists: high affinity for mu receptors and low for kappa and delta. They include: Morphine: • Meperidine (pethidine) • a. Less analgesic, less effect on cough or resp. depression and not delay labor. b. Has atropine & anti-H1 like action no miosis, less constipation or urine retention, effective in colic • Methadone: It is mainly used to relieve the withdrawal symptomsof morphine or heroin

  13. Types of opioid analgesics • B. Mixed agonists-antagonists: . Agonist at k-receptors, antagonists at mu. . They excitation, dysphoria &hallucinations, less Resp depression C. Opioid antagonists • Naloxone: IV, 1h duration used in Opioid overdose • Naltrexone: Oral, 48h duration, used in • Maintenance programs in treating addiction, alcoholism

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