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Analgesics

Analgesics. Pain. Pain receptors are nerves that transmit pain . Respond to thermal , mechanical and chemical stimuli . Impulse generated . Arrives at spinal cord and brain (CNS). Prostaglandins and leukotrienes make pain receptors more sensitive . Analgesics.

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Analgesics

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  1. Analgesics

  2. Pain • Painreceptors are nervesthattransmitpain. • Respondtothermal, mechanical and chemicalstimuli. • Impulse generated. • Arrives at spinalcord and brain (CNS). • Prostaglandins and leukotrienesmakepainreceptors more sensitive.

  3. Analgesics • Drugsthat relieve pain. • Mildanalgesics (aspirin, Paracetamol, Ibuprofen) • Non-addictive. • StrongOpiates (morphine, heroin, codeine) • Addictive (controlledsubstances). • Local anaesthetics (lidocaine in dentistry) • General anaesthetics (unconsciousness, insensitivity)

  4. MildAnalgesics • Indirectlyblockingenzyme-controlledsynthesis of prostaglandins. • Reduce pain, fever and inflammation.

  5. Natural Painkillers • Endorphins and enkephalins • Bindtoneuro-receptors in brainrelievingpain. • Stronganalgesics (opiates) workbybindingtoopiatereceptors in brain, preventingtransmission of painimulses.

  6. Differentmechanisms… Aspirin Morphine Actsdirectlyonbrain. Works byactingoninflammedtissue and associatednerves.

  7. Uses of derivatives of salicylicacid • Mildanalgesic (aches, pains, headaches, sunburn, arthritis) • Anti-pyretic (reduces fever) • Anti-inflammatoryagent. • Anti-plateletagent (prevention of bloodclottingafterheartsurgery)

  8. Prevention of bloodclotting • Resultsfrominhibitingproduction of prostaglandins. • These are hormone-likefattyacidsthat cause bloodplateletstosticktogether (clot) • Foundtopreventrecurrance of heartattacks in moderateamounts.

  9. Disadvantages of Aspirin • Stomachupset and internalbleeding , ulceration– duetoacidity. • Gastrointestinal bleedingfollowing alcohol use. • Skinrashes, respiratorydifficulties (for 0.5%) • Accidental poisoning in infants. • Reye’ssyndrome in children (liver and braindisorder)

  10. Substitutesexist… Phenacetin Acetaminophen

  11. Uses of acetaminophen…. • Likeaspirin, an anti-pyreticreducingfever. • As ananalgesicto reduce mildpain. • Doesnotupsetstomach, butisnotaneffective anti-inflammatorydrug. • Safe, preferreddrugforthosewithaspirinallergy. • Notto be takenwith alcohol. • Overdose (>20 tablets) can be serious (braindamage, death)

  12. Ibuprofen • Sameeffects as aspirin. • Fewerstomachproblems. • Wide safety margin. • Kidneyproblems in large doses.

  13. StrongAnalgesics • «opiates» or «narcoticanalgesics» • Morphineistheprinciplealkaloid (nitrogencontainingorganiccompound) • 10% of rawopium. • Codeineis 0.5% rawopium. • Heroinissynthesisedbychangingtwo –OH groupsonmorphinetotwoester (CH3COO-) groups. • Heroinistherforesemi-synthetic.

  14. Question • Look at structures of heroin, codeine and morphine at top of page 414. Whatfunctionalgroups do theyhave ? How do theydiffer ?

  15. Advantages and Disadvantages of Opiates • Use page 414 totake notes on…. • Pharmacologicaleffects • Medical uses • Psychologicaleffects • Tolerance and dependence

  16. Questions • 4, 5 and 6 on page 434.

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