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2.dental local anesth new

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Pharmacology
Third Year

Published in: Health & Medicine
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2.dental local anesth new

  1. 1. Drugs that cause reversible block of nerve conduction producing transient localized anesthesia without significantly affecting consciousness.
  2. 2. According to their chemical structure:  Esters: Cocanie, Procaine, Benzocaine & Tetracaine  Amides: Lidocanie (xylocaine, ligocaine), Prilocaiine, Mepivacaine & Dibucaine.
  3. 3. According to their solubility & therapeutic application: - Soluble Local anesthetics suitable for injection: Procaine HCl, Lidocaine HCl - Soluble Local anesthetics used only topically on the eye: Cocaine HCl - Local anesthetics of low solubility used as powders & ointments: Benzocaine
  4. 4. According to their potency  LA with weak potency & short duration(30-60 min) Examples: Procaine Chloroprocaine  LA with moderate potency and intermediate duration (1 - 3 hrs) Examples: Lidocaine (xylocaine) Prilocaine.  LA with high potency and long duration(3 – 6 hrs) Examples: Tetracaine Bupivacaine
  5. 5. Mechanism of action: local anesthesia blocks voltage dependent sodium channels from inside the nerve fiber. → prevention of sodium permeability into the nerves → membrane stabilization → ↓ impulse generation and propagation At alkaline tissue pH= 7.4 They are Unionized molecules → pass easily through membrane lipid of nerve fiber → reach cytoplasm ( ionized + unionized)→ the ionized form bind to Na+ channels blocking Na+ influx prevent initiation of AP
  6. 6. Mechanism of action:
  7. 7. Action Local anesthetic action  Small fibers before large  Demylinated before mylinated fiber  Sympathetic & pain → temperature → touch& pressure → motor fibers  Recovery → reverse direction. Addition of adrenaline→ vasoconstriction→ ↓absorption of LA →↓spread →↑duration& ↓toxicity
  8. 8. Metabolism : Esters are fastly metabolized by plasma and tissues esterases. Thus , they have short duration. They are metabolized to PABA (cause allergy in some individuals). Amides are metabolized slowly by liver microsomal enzymes. Thus , they have longer duration
  9. 9. Methods of administration and uses  Surface anesthesia: Direct application of the drug on accessible surface as skin or mucous membrane LA with short or intermediate duration are used for this purpose. Dosage forms: Powder , Solutions (spray) , Creams or Ointments. Benoxinate ( ester LA) used in ophthalmology for corneal anesthesia because :  No mydriasis.  No corneal injury. Benzocaine used in form of powder or cream on skin wounds or ulcer, because it is insoluble produces less systemic toxicity
  10. 10. Methods of administration and uses (cont.)  Infiltration anesthesia: They are injected directly into the tissue by S.C injection e.g wound suturing & cysts removal , Circumcisions .  Nerve block anesthesia: The anesthetic in injected close to the appropriate nerve trunks or peripheral nerve at a site proximal to where anesthesia is desired. e.g. dental anesthesia
  11. 11. Methods of administration and uses (cont.)  Sympathetic block: It is injected around sympathetic ganglion.  Para vertebral block: injected around spinal roots as they emerge from the paravertebral foramina.  Caudal anesthesia: injected in sacral canal.
  12. 12. Methods of administration and uses (cont.)  Spinal anesthesia: LA injected in the subarachnoid space in the lumbar region.  Epidural anesthesia Anesthetics injected in epidural space Uses  abdominal, pelvic and lower limbs surgery in patients unsuitable for general anesthesia.  Epidural anesthesia is frequently used for painless childbirth. Some local anesthetic used for Treatment of cardiac dysrhythmia e.g. Lidocaine
  13. 13. Side effects The side effects of LA are usually minimum , because they are applied Locally. They are combined with a vasoconstrictors such as adrenaline to decrease systemic absorption. But some side effects may occur due to :High dose is administered OR They are injected (mistakenly ) into blood vessels LA Side effects are  Restlessness, headache &convulsions followed by respiratory depression  hypotension and bradycardia  Hypersensitivity reaction (with ester type)  Mucosal irritation (cocaine, dibuacine). Side effects are more with local anesthetic that are potent and have long duration
  14. 14. Influencing Factors Dosage, high dose cause:  Fast onset  Longer duration.  Increase risk of side effects. Site of administration : high vascularity cause:  Short duration.  High risk of side effects. Lipid solubility of LA: more lipid soluble more effective. Infections/ inflammations cause: - low pH decrease action : LA are bases thus at low pH they become more ionized . This will reduce their penetrations across membranes this reduces their effects. - Vasodilation This Increases absorption to blood and increase risk of side effects and reduce duration of LA.
  15. 15. (LA- Influencing Factors (cont. Type of solution : Alkalinization of LA solution :  Less painful.  Increases non ionization (uncharged)  Increases diffusion through nerve  Increases effects.  Produce fast onset. Addition of vasoconstrictor ( epinephrine) will:  Decreases vascular absorption.  Increases duration.  Decreases risk of side effects.  Contraindicated when LA injected around end arteries ( fingers, toes, ear lobes, nose) may lead to ischemia and gangrene
  16. 16. Other Methods of producing local anesthesia Application of cold: Cooling decreases excitability and conductivity of nerve Ischemia to tissues: by depriving any tissue from its blood supply e.g. by tourniquet. Paralysis of sensory nerve endings or fibers with drugs: Astringents may lead to local anesthesia by precipitating nerve proteins e.g. ethyl alcohol injected perineurally in trigeminal neuralgia
  17. 17. Thank you

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