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Lab ≠ 5 Analgesics Prepared By: T.A Samiah Al- Shehri

Lab ≠ 5 Analgesics Prepared By: T.A Samiah Al- Shehri. Definition:. Analgesics are drugs that selectively inhibit the perception “sensation” of pain. Types of pain:. 1- Superficial : Stimulation of skin & mucous membrane . Fast response “Withdraw of limb” . 2- Deep :

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Lab ≠ 5 Analgesics Prepared By: T.A Samiah Al- Shehri

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  1. Lab ≠ 5AnalgesicsPrepared By:T.A Samiah Al-Shehri

  2. Definition: Analgesics are drugs that selectively inhibit the perception “sensation” of pain

  3. Types of pain: 1-Superficial: • Stimulation of skin & mucous membrane . • Fast response “Withdraw of limb” . 2-Deep: • Stimulation of muscles, joints, tendons, heart etc • Slow response “Sweating, Nausea & Vomiting” .

  4. Classification of analgesic drugs: A- Peripheral analgesics : 1- Causal . 2- Non- Causal . B- Central analgesics : 1- Narcotics . 2- Non- Narcotics .

  5. Peripheral Analgesics :

  6. 2. Central Analgesics :

  7. Central Analgesics :

  8. Central Analgesics :

  9. Screening methods for analgesics: Principle: Pain is induced in a suitable animal & the response of the animal to the painful stimuli is recorded before & after administration . 1- Narcotics: A- Thermal methods: Hot-plate Heat is the painful stimuli Tail flick B-  Mechanical method: By applying a pressure to the rats tail .

  10. Screening methods for analgesics: 2- Non- narcotics: A- Electrical method: Applying certain voltage to the metallic rods in order in order to produce pain to animal . B- Chemical method: By inject the irritant substance as acetic acid or parabenzoquinonee.g. Writhing method

  11. Hot-plate method: Animal: Mouse . Instrument: Hot-Plate Analgesiometer . Painful stimuli: Heat 55⁰C . Drug used: Morphine 0.5% 25mglkg . Animal response: licking of feet or trying to jumping out of the beaker .

  12. Hot-plate method: Procedure: • Calculate the dose according to the animal weight . • Adjust the temperature of the hot plate at 55⁰C . • Drop the mouse on the hot-plate, the animal will shows signs of discomfort following by licking of feet or trying to jumping out of the beaker . • The normal reaction time is determined (which is the time from dropping the animal inside the beaker until it licks its feet or jumps out of the beaker). Normally occur within 20sec.

  13. Inject the dose of morphine IP, wait 5min and the reaction time determined again after 5, 10, 15min .

  14. Tail-flick method : • Animal: Mouse . • Instrument: Tail-flick Analgesiometer . • Painful stimuli: Heat 130⁰C . • Drug used: Morphine 0.5% 25mglkg. • Animal response: flicking of the tail "cutoff point“ .

  15. Tail-flick method : Procedure: • Cover the animal body except the tail leave it exposed to a heat from beam of light at 130⁰C . • Animal response by flicking the tail which should be less than or equal to 6 sec "cutoff point“ .

  16. Tail-flick method : Procedure • Calculate the required dose of morphine and injected the animal IP, wait 5min then record the reaction time every 5, 10, 15min . • Calculate the % maximal possible effects (%MPE) .

  17. Tail-flick Analgesiometer :

  18. Writhing method : Principle: The painful stimuli induced by IP injection of irritant substance e.g. Acetic acid, quinine . Definition of writhing: Stretching of the body, withdrawing up the lower limb, retraction of the abdomen & stomach touch the ground . Material: - Animal: mouse . - Painful stimuli: acetic acid 0.6% 1ml/100gm IP . - Drug: Na salicylate 2% , 100mg/kg & 200mg/kg IP .

  19. Writhing method : Procedure: Control mouse: Inject the calculated dose of acetic acid IP, mouse response by writhing. Count the number of writhes per 10min To a second mouse: Inject the Na salicylate 100mg/kg IP, wait for 5min. then inject the dose of acetic acid then calculate the onset & the number of writhing . To a third mouse : Inject the Na salicylate 200mg/kg IP, wait for 5min. then inject the dose of acetic acid then calculate the onset & the number of writhing.

  20. Result :

  21. N.B. • After treatment with Na salicylate the onset of writhing will delayed and the No. of writhing will decrease this explain the analgesic property of NSAIDs . • The No. of writhing measured within 10min after the onset time .

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