Y2 s1 nmj blockers

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Y2 s1 nmj blockers

  1. 1. Neuromuscular junction blockers Prof. Vajira Weerasinghe Dept of Physiology
  2. 2. NMJ blocking <ul><li>Useful in general anaesthesia to facilitate inserting tubes </li></ul><ul><li>Muscle paralysis is useful in performing surgery </li></ul>
  3. 3. Earliest known muscle relaxant - Curare <ul><li>Curare has long been used in tropical South America as an extremely potent arrow poison </li></ul><ul><li>Darts were tipped with curare and then accurately fired through blowguns made of bamboo </li></ul><ul><li>Death for birds would take one to two minutes, small mammals up to ten minutes, and large mammals up to 20 minutes </li></ul><ul><li>Tubocurarine was later used </li></ul><ul><li>Atracurium is now used </li></ul>
  4. 4. Neuromuscular blocking agents <ul><li>Non-depolarising type (competitive) </li></ul><ul><ul><li>Act by competing with Ach for the Ach receptors </li></ul></ul><ul><ul><li>Binds to Ach receptors and blocks </li></ul></ul><ul><ul><li>Prevent Ach from attaching to its receptors </li></ul></ul><ul><ul><li>No depolarisation </li></ul></ul><ul><ul><li>Ach can compete & the effect overcomes by an excess Ach </li></ul></ul><ul><ul><li>Anticholinesterases can reverse the action </li></ul></ul><ul><ul><li>eg. </li></ul></ul><ul><ul><ul><li>Curare </li></ul></ul></ul><ul><ul><ul><li>Tubocurarine </li></ul></ul></ul><ul><ul><ul><li>Gallamine </li></ul></ul></ul><ul><ul><ul><li>Atracurium </li></ul></ul></ul>
  5. 5. Neuromuscular blocking agents <ul><li>Depolarising type (non-competitive) </li></ul><ul><ul><li>Act like Ach, but resistant to AchE action </li></ul></ul><ul><ul><li>Bind to motor end plate and once depolarises </li></ul></ul><ul><ul><li>Persistent depolarisation leads to a block </li></ul></ul><ul><ul><ul><li>Due to inactivation of Na channels </li></ul></ul></ul><ul><ul><li>Ach cannot compete </li></ul></ul><ul><ul><li>eg. </li></ul></ul><ul><ul><ul><li>suxamethonium </li></ul></ul></ul><ul><ul><ul><li>Ach in large doses </li></ul></ul></ul><ul><ul><ul><li>nicotine </li></ul></ul></ul>
  6. 6. Neuromuscular blocking agents <ul><li>AchE inhibitors </li></ul><ul><ul><li>Inhibit AchE so that Ach accumulates and causes depolarising block </li></ul></ul><ul><li>Reversible </li></ul><ul><ul><li>Competitive inhibitors of AChE </li></ul></ul><ul><ul><li>Block can be overcome by curare </li></ul></ul><ul><ul><ul><li>physostigmine, neostigmine, eserine, edrophonium </li></ul></ul></ul><ul><li>Irreversible </li></ul><ul><ul><li>Binds to AChE irreversibly </li></ul></ul><ul><ul><ul><li>, insecticides, nerve gases </li></ul></ul></ul>
  7. 7. Na + Acetylcholine Depolarization Na + - - - - + + + + - - - - + + + + + + + + + + + + - - - - - - - -
  8. 8. Na + Acetylcholine Tubocurarine Na + + + + + - - - - - - - - + + + + Competitive neuromuscular blocking drugs
  9. 9. Repolarized + + + + - - - - + + + + - - - - - - - - + + + + - - - - + + + + Depolarizing Neuromuscular blocking drugs PHASE II Membrane repolarizes but the receptor is desensitized to effect of acetylcholine
  10. 10. Na + Depolarized Na + - - - - + + + + + + + + - - - - - - - - + + + + + + + + - - - - - - - - Depolarizing Neuromuscular blocking drugs PHASE I Membrane depolarizes resulting in an initial discharge which produces transient fasciculations followed by flaccid paralysis

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