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Local anesthesia

Local anesthesia

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Local anesthesia

  1. 1. LOCAL ANESTHESIA Dr. Amitha Dept of Oral pathology
  2. 2. CONTENTS  DEFINITION  CLASSIFICATION  MECHANISM OF ACTION  COMPOSITION  LOCAL ANESTHETIC AGENTS  VASOCONSTRICTORS
  3. 3. DEFINITION:  IT IS THE LOSS OF SENSATION IN A CIRCUMSCRIBED AREA OF THE BODY CAUSED BY A DEPRESSION OF EXCITATION IN NERVE ENDINGS OR AN INHIBITION OF THE CONDUCTION PROCESS IN PERIPHERAL NERVES
  4. 4. CLASSIFICATION  ESTERS  ESTERS OF BENZOIC ACID:  BUTACAINE  COCAINE  BENZOCAINE (ETHYL AMINO BENZOATE)  TETRACAINE  ESTERS OF PARA- AMINOBENZOIC ACID  CHLORPROCAINE  PROCAINE  PROPOXYCAINE  AMIDES  ATRICAINE  BUPIVACAINE  DIBUCAINE  ETIDOCAINE  LIDOCAINE  MEPIVACAINE  PRILOCAINE  ROPIVACAINE  QUINOLINE  CENTIBUCRIDINE
  5. 5. Esters vs Amides  The ester linkage is more easily broken so the ester drugs are less stable in solution and cannot be stored for as long as amides.  Amide anaesthetics are also heat-stable.  The metabolism of most esters results in the production of para- aminobenzoate (PABA) which is associated with allergic reaction.  Amides, in contrast, very rarely cause allergic phenomena. For these reasons amides are now more commonly used than esters.
  6. 6. BASED ON MODE OF APPLICATION  INJECTABLE  LOW POTENCY, SHORT DURATION  PROCAINE  INTERMEDIATE POTENCY AND DURATION  LIGNOCAINE (LIDOCAINE)  HIGH POTENCY, LONG DURATION  TETRACAINE, BUPIVACAINE, ROPIVACAINE, DIBUCAINE  SURFACE/TOPICAL  SOLUBLE  COCAINE, LIGNOCAINE, TETRACAINE, BENOXINATE  INSOLUBLE  BENZOCAINE, BUTYLAMINOBENZOATE (BUTAMBEN)
  7. 7. BASED ON DURATION  ULTRA SHORT ACTING (<30 MINUTES)  PROCAINE WITHOUT VASOCONSTRICTOR  2% LIDOCAINE WITHOUT VASOCONSTRICTOR  SHORT ACTING (45-75 MINUTES)  2% LIDOCAINE WITH 1:100,000 EPINEPHRINE  4% PRILOCAINE WHEN USED FOR NERVE BLOCK  MEDIUM ACTING (90-150 MINUTES)  2% LIDOCAINE + 2% MEPIVACAINE WITH A VASOCONSTRICTOR  4% PRILOCAINE WITH 1:200,000 EPINEPHRINE  LONG ACTING (180 MINUTES OR LONGER)  0.5% BUPIVACAINE 1:200,000 EPINEPHRINE
  8. 8. ACCORDING TO BIOLOGICAL SITE AND MODE OF ACTION CLASS A AT RECEPTOR SITE ON EXTERNAL SURFACE OF NERVE MEMBRANE BIOTOXIN TETRODOTOXIN CLASS B AT RECEPTOR SITE ON INTERNAL SURFACE OF NERVE MEMBRANE QUATERNARY AMMONIUM ANALOGUES OF LIDOCAINE SCORPION VENOM CLASS C BY A RECEPTOR INDEPENDENT PHYSICOCHEMICAL MECHANISM BENZOCAINE CLASS D BY COMBINATION OF RECEPTOR AND RECEPTOR CLINICALLY USEFUL LOCAL ANESTHETIC AGENTS
  9. 9. MECHANISM OF ACTION  ALTERING THE RESTING POTENTIAL OF THE NERVE MEMBRANE  ALTERING THE THRESHOLD POTENTIAL (FIRING LEVEL)  DECREASING THE RATE OF DEPOLARIZATION  PROLONGING THE RATE OF REPOLARIZATION
  10. 10. Effect of PH  Local anesthetics are weak bases and are usually formulated as the hydrochloride salt to render them water-soluble.  At the chemical's pKa the protonated (ionized) and unprotonated (unionized) forms of the molecule exist in an equilibrium but only the unprotonated molecule diffuses readily across cell membranes.  Once inside the cell the local anesthetic will be in equilibrium, with the formation of the protonated (ionized form), which does not readily pass back out of the cell. This is referred to as "ion-trapping".
  11. 11. Effect of PH  LA are weak bases and their activity increases by increasing PH  This because if large amount of a drug is unpolar, it will facilitate its penetration through the cell membrane  Once the drug has penetrated the lipid barrier and reach its site of action it ionized and the ionized form is responsible for LA activity
  12. 12.  Acidosis such as caused by inflammation at a wound partly reduces the action of local anesthetics.  This is partly because most of the anesthetic is ionized and therefore unable to cross the cell membrane to reach its cytoplasmic-facing site of action on the sodium channel.
  13. 13.  Local anesthetics block conduction in the following order: small myelinated axons (e.g. those carrying nociceptive impulses), non- myelinated axons, then large myelinated axons. Thus, a differential block can be achieved (i.e. pain sensation is blocked more readily than other sensory modalities).
  14. 14.  Disruption of ion channel function via specific binding to sodium channels, holding them in an inactive state.  Disruption of ion channel function by the incorporation of local anaesthetic molecules into the cell membrane .
  15. 15.  Small nerve fibres are more sensitive than large nerve fibres  Myelinated fibres are blocked before non-myelinated fibres of the same diameter.  Thus the loss of nerve function proceeds as loss of pain, temperature, touch, proprioception, and then skeletal muscle tone. This is why people may still feel touch but not pain when using local anaesthesia.
  16. 16.  THEORIES  THE ACETYLCHOLINE THEORY  THE CALCIUM DISPLACEMENT THEORY  THE SURFACE CHARGE THEORY  THE MEMBRANE EXPANSION THEORY  THE SPECIFIC RECEPTOR THEORY
  17. 17. CALCIUM IONS DISPLACED FROM SODIUM CHANNEL RECEPTOR SITE ↓ LOCAL ANESTHETIC MOLECULE BINDS TO THIS SITE ↓ BLOCKADE OF SODIUM CHANNEL ↓ DECREASE IN SODIUM CONDUCTION ↓ DEPRESSION OF RATE OF ELECTRICAL DEPOLARIZATION ↓ FAILURE TO ACHIEVE THRESHOLD POTENTIAL ↓ LACK OF DEVELOPMENT OF ACTION POTENTIAL ↓ CONDUCTION BLOCKADE MEMBRANE EXPANSION THEORY SPECIFIC RECEPTOR THEORY
  18. 18. The duration of action  The duration of action of the drug is also related to the length of the intermediate chain joining the aromatic and amine groups.  Protein binding , Procaine is only 6% protein bound and has a very short duration of action, wherease bupivacaine is 95% protein bound. bupivacaine have a longer duration of action .
  19. 19. Absorption and distribution  Some of the drug will be absorbed into the systemic circulation: how much will depend on the vascularity of the area to which the drug has been applied.  The distribution of the drug is influenced by the degree of tissue and plasma protein binding of the drug. the more protein bound the agent, the longer the duration of action as free drug is more slowly made available for metabolism.
  20. 20. Metabolism and excretion  Esters (except cocaine) are broken down rapidly by plasma esterases to inactive compounds and consequently have a short half life. Cocaine is hydrolysed in the liver. Ester metabolite excretion is renal.  Amides are metabolised hepatically by amidases. This is a slower process, hence their half-life is longer and they can accumulate if given in repeated doses or by infusion.
  21. 21. Adverse Effects  CNS: excitation followed by depression (drowsiness to unconsciousness and death due to respiratory depression.  Cardiovascular System: bradycardia, heart block, vasodilation (hypotension)  Allergic reactions: allergic dermatitis to anaphylaxis (rare, but occur most often by ester-type drugs).
  22. 22. COMPOSITION OF LOCAL ANESTHETIC AGENT  LIGNOCAINE 2%  VASOCONSTRICTOR- ADRENALIN  SODIUM META BISULPHITE 0.5mg (ANTIOXIDENT)  METHYL PARABEN (PRESERVATION)  THYMOL (ANTIFUNGAL)  WATER (TO MAINTAIN VOLUME)  NaCl (ISOTONICITY)  PHENTOLAMINE (REVERSING AGENT)  INSTEAD OF METHYL PARABEN- CAPRYL HYDROCAPRINO TOXIN
  23. 23. LOCAL ANESTHETIC AGENTS  ESTER DERIVATIVES  PROCAINE  DIETHYLAMINOETHYL ESTER OF PABA BY EINHORN IN 1905  AVAILABLE AS 4% SOLUTION  ALSO AVAILABLE IN 2% SOLUTION IN COMBINATION WITH 0.4% PROPOXYCAINE AND 1:30,000 LEVARTERENOL OR 1:20,000 LEVONORDEFRIN
  24. 24.  PROCAINE IS A WHITE CRYSTALLINE POWDER  SLIGHTLY SOLUBLE IN WATER  MOST COMMONLY USED AS HYDROCHLORIDE SALT  PROCAINE IS COMPARATIVELY WEAK ANESTHETIC  LOW DEGREE OF TOXICITY  STANDARD OF TOXICITY AND POTENCY  ASSIGNED A POTENCY AND TOXICITY OF 1  PROFOUND VASODILATOR  0.5 TO 1 gm SLOWLY OVER SUFFICIENT PERIOD
  25. 25. • PROCAINE IS HYDROLYZED TO PABA AND DIETHYLAMINOETHANOL WITHIN THE PLASMA • ONSET OF ANALGESIA DEPENDS ON THE CONCENTRATION AND METHOD EMPLOYED • WHEN INFILTRATED AROUND FREE NERVE ENDINGS ONSET IS ALMOST IMMEDIATE • PULPAL ANALGESIA IS ABOUT 30 MINUTES
  26. 26.  NERVOUS SYSTEM:  READILY CROSSES THE BLOOD BRAIN BARRIER  PRODUCES BOTH STIMULATION AND DEPRESSION OF CNS CVS:  DEPENDS MAINLY ON THE AMOUNT OF DRUG USED  SYSTEMICALLY DEPRESSES SMOOTH, CARDIAC AND SKELETAL MUSCLES  EFFECT ON HEART IS QUINIDINE LIKE  IN LARGE DOSES MAY PRODUCE HYPOTENSION RESPIRATORY SYSTEM:  LOCAL ANESTHETIC DOSE HAS LITTLE DIRECT EFFECT
  27. 27. TETRACAINE  TETRACAINE (PARA-BUTYLAMINOBENZOYL-2- DIMETHYLAMINOETHANOL HYDROCHLORIDE)  WHITE COLOURLESS POEDER  SOLUBLE IN WATER ( 1gm IN 7 ml WATER)  USED AS HYDROCHLORIDE SALT  pH 5.9  POTENT RELATIVELY TOXIC LOCAL ANESTHETIC AGENT
  28. 28. • RAPIDLY DECOMPOSED BY ALKALI • pKa 8.5 • COMPATIBLE WITH SULFONAMIDES AND ALL VASOCONSTRICTORS • AVAILABLE IN 0.15%, 1% AND 2% TOPICAL ONLY • POPULAR FOR SPINAL ANESTHESIA • BIOTRANSFORMATION IN THE LIVER AND END PRODUCTS ELIMINATED BY THE KIDNEYS • CHEMICALLY RELATED TO PROCAINE BUT PHARMACOLOGICALLY CLOSER TO COCAINE
  29. 29.  POTENT TOPICAL ANESTHETIC WITH NO SIGNIFICANT VASODILATION PROPERTY  WHEN INJECTED WITHOUT A VASOCONSTRICTOR PRODUCES 30 TO 45 MINUTES OF ANALGESIA  SAME CONCENTRATION WITH 1:100,000 EPINEPHRINE PRODUCES 75 TO 120 MINUTES OF ANALGESIA  MAXIMUM DOSE: 20mg (1ml OF 2% SOLUTION)  NON IRRITATING  CNS AND CVS EFFECTS ARE SIMILAR TO THOSE OF PROCAINE
  30. 30. PROPOXYCAINE  2-DIETHYLAMINOETHYL 4-AMINO-2- PROPOXYBENZOATE  USED AS HYDROCHLORIDE SALT  pH 5.5  POTENT LOCAL ANESTHETIC  EQUAL IN POTENCY AND TOXICITY TO TETRACAINE  PARTIALLY HYDROLIZED IN PLASMA  UNDERGOES FURTHER BIOTRANSFORMATION IN LIVER
  31. 31. • ELIMINATED BY KIDNEYS • RAPID ONSET • PROFOUND ANESTHESIA OF LONG DURATION WHEN INJECTED CLOSE TO THE NERVE SHEATH • MAXIMUM DOSE 6.6 mg/Kg (3mg/ Ib) • MAXIMUM TOTAL ANESTHETIC DOSAGE SHOULD NOT EXCEED 400 mg
  32. 32. 2-CHLORPROCAINE  BETA-DIETHYLAMINOETHYL-2-CHLORO-4- AMINOBENZOATE  pH 4.8  THE SUBSTITUTION OF A CHLORIDE ATOM IN THE BENZENE RING OF PROCAINE CAUSES A FOURFOLD IN THE HYDROLYSIS RATE  MORE POTENT AND LESS TOXIC THAN PROCAINE  RAPIDLY HYDROLYZED IN THE PRESENCE OF PLASMA CHOLINESTERASE
  33. 33. • BYPRODUCTS ELIMINATED THROUGH KIDNEYS • 1.2% OR 3% CONCENTRATION IS USED • NON IRRITATING TO TISSUE • SHORT DURATION, IT MUST BE USED WITH VASOCONSTRICTOR • USED IN CHILDREN • MAXIMUM DOSE: 11mg/Kg OR 800mg (40ml OF 3% SOLUTION)
  34. 34. LIDOCAINE  IN 1943 BY LOFGREN  IT IS THE FIRST NON ESTER TYPE OF LOCAL ANESTHETIC  LIDOCAINE BASE IS ONLY SLIGHTLY WATER SOLUBLE, THE HYDROCHLORIDE SALT IS READILY SOLUBLE IN WATER  IS THE STANDARD OF COMPARISION  DIFFUSES READILY THROUGH INTERSTITIAL TISSUE AND IN TO THE LIPID RICH NERVE
  35. 35.  RAPID ONSET OF ANESTHESIA  pKa 7.85 FAVORS DEPROTONIZATION AND PRODUCES UNIONIZED FREE BASE AND PRODUCTION OF CONDUCTION BLOCK  2 TIMES AS POTENT AND TOXIC AS PROCAINE  ONSET TIME IS OF ABOUT 2 TO 3 MINUTES  DURATION OF ACTION DEPENDS ON TYPE OF INJECTION AND AMOUNT OF VASOCONSTRICTOR
  36. 36.  NERVOUS SYSTEM:  IN TOXIC DOSES FIRST PRODUCES STIMULATION AND THEN DEPRESSION OF CNS  IV LIDOCAINE IS CAPABLE OF PRODUCING A DEGREE OF ANALGESIA AND GENERAL ANESTHESIA  CVS:  50 TO 100 mg (1.5 mg/Kg) GIVEN IV DURING GENERAL ANESTHESIA AND SURGERY TO CORRECT VENTRICULAR ARRHYTHMIAS  TOXIC DOSE : HYPOTENSION AND CARDIOVASCULAR COLLAPSE  RESPIRATORY SYSTEM:  SMALL DOSE HAS A MILD BRONCHODILATING EFFECT  RESPIRATORY ARREST IS THE MOST COMMON CAUSE OF DEATH RELATED TO OVER DOSE
  37. 37.  LIDOCAINE UNDERGOES BIOTRANSFORMATION IN THE LIVER RATHER THAN HYDROLYSIS IN THE PLASMA  LIDOCAINE AND ITS BYPRODUCTS ARE ELIMINATED BY THE KIDNEYS  4-HYDROXY-2,6-DIMETHYLANILNINE IS THE MAJOR URINIARY METABOLITE  MAXIMUM DOSE: 4.4 mg/Kg (2mg/lb)
  38. 38. • NOT TO EXCEED 300mg WHEN NOT USED WITH A VASOCONSTRICTOR • 7mg/Kg (3.2 mg/lb) • NOT TO EXCEED 500mg WHEN USED WITH EITHER 1:50,000 OR 1:100,000 EPINEPHRINE • DENTAL CARTRIDGES OF 2% LIDOCAINE ARE AVAILABLE AND CONTAIN NO VASOCONSTRICTOR OR EPINEPHRINE IN CONCENTRATIONS OF 1:100,000 OR 1:50,000
  39. 39. MEPIVACAINE  MOLECULAR WEIGHT 285.5  WITHOUT A VASOCONSTRICTOR PULPAL ANALGESIA OF 20 TO 40 MINUTES  MODERATELY LONG DURATION OF ACTION  2 TIMES AS POTENT AND TOXIC AS PROCAINE  CURRENTLY MEPIVACAINE (COOK-WAITE LABORATORIES), LIDOCAINE AND PRILOCAINE (ASTRA PHARMACEUTICALS) ARE THE ONLY DENTAL CARTRIDGES THAT DO NOT CONTAIN THE GERMICIDE OR PRESERVATIVE METHYL PARABEN, WHICH HAS BEEN IMPLICATED AS THE CAUSATIVE AGENT IN MANY ALLERGIC REACTIONS
  40. 40.  IT IS A PABA DERVATIVE  MAY ALSO BE RESPONSIBLE FOR CROSS SENSITIVITY BETWEEN ESTER AND NON ESTER ANESTHETIC AGENTS  MAXIMU DOSE: WITH OR WITHOUT A VASOCONSTRICTOR IS 6.6mg/Kg (3mg/lb) NOT TO EXCEED 400mg  AVAILABLE IN 3% CONCENTRATION WITHOUT VASOCONSTRICTOR OR A 2% SOLUTION WITH 1:20,000 LEVONORDEFRIN
  41. 41. PRILOCAINE  DERIVATIVE OF TOLUIDINE INSTEAD OF XYLIDINE  EMPIRICAL FORMULA OF BASE : C13H20N20  MOLECULAR WEIGHT: 220.3  HYDROCHLORIDE SALTS ARE USED HAVING EMPIRICAL FORMULA OF C13H21Cl N20  CONTAINS 86% BASE AND HAVING A MOLECULAR WEIGHT OF 256.8
  42. 42.  4% SOLUTION OF PRILOCAINE HAS A PH of 6.0 – 7.0  pKa is 7.9  ABOUT 40% LESS TOXIC THAN LIDOCAINE  UNDERGOES BIOTRANSFORMATION MORE RAPIDY THAN LIDOCAINE  ORTHOTULUIDINE A METABOLITE PRODUCES METHEMOGLOBIN IN LARGE DOSES  CONTRAINDICATED IN PATIENTS WITH CONGENITAL OR IDIOPATHIC METHEMOGLOBINEMIA
  43. 43. • 400mg PRODUCES A METHEMOGLOBIN LEVEL OF ONLY ABOUT 1% IN THE BLOD • LEVELS LESS THAN 20% RARELY PRODUCE SYMPTOMS • SYMPTOMS INCLUDE: CYANOSIS COUPLED WITH RESPIRATORY OR CIRCULATORY DISTRESS • SYMPTOMS MAY BE REVERSED WITH IV ADMINISTRATION OF 1-2mg/Kg OF 1% METHYLENE BLUE
  44. 44.  AVAILABLE IN 4% SOLUTION WHICH WITHOUT EPINEPHRINE GIVES 60 MINUTES OF WORKING ANESTHESIA  WHEN EPINEPHRINE IN A 1:200,000 CONCENTRATION IS ADDED TO 4% CITANEST THE PRODUCT IS CALLED CITANEST FORTE  DURATION OF PULPAL ANALGESIA IS ABOUT 60-90 MINUTES 
  45. 45. BUPIVACAINE  CRYSTALLINE POWDER FREELY SOLUBLE IN 95% ETHANAL AND WATER AND SLIGHTLY SOLUBLE IN CHLOROFORM OR ACETONE  PH 4.5-6.5 AND pKa IS 8.1  AMIDE DERIVATIVE STRUCTURALLY SIMILAR TO MEPIVACAINE WITH A BUTYL GROUP REPLACING THE METHYL GROUP IN THE HYDROPHYLIC END  MARCAINE: BUPIVACAINE, 0.5% WITH 1:200,000 EPINEPHRINE AVAILABLE IN CONVENTIONAL 1.8 ml CARTRIDGE  ALSO SUPPLIED IN 10, 2O AND 50 ml VIALS CONTAINING 0.25%, 0.5% OR 0.75% SOLUTION WITHOUT A VASOCONSTRICTOR OR WITH 1:200,000 EPINEPHRINE
  46. 46. • STRUCTURAL MODIFICATION HAS RESULTED IN THE PRODUCTION OF AN AGENT THAT HAS 35 FOLD INCREASE IN OIL WATER PARTITION COEFFICIENT PLUS A SIGNIFICANT INCREASE IN PROTEIN BINDING QUALITIES • THE NET EFFECT IS A 4 FOLD INCREASE IN INTRINSIC ANESTHETIC ACTIVITY AND DURATION OF ACTION • IT IS 4 TIMES AS POTENT AND TOXIC AS MEPIVACAINE AND LIDOCAINE • PULPAL ANESTHESIA IS INCREASED TO 3 HOURS • DURATION OF SOFT TISSUE ANESTHESIA MAY EXTEND TO 12 HOURS
  47. 47. • A PERIOD OF ANELGESIA PERSISTS AFTER THE RETURN OF OTHER SENSATIONS, HENCE THE NEED OF ANALGESIC DRUG IS REDUCED OR ELIMINATED • SHOULD NOT BE ADMINISTERED TO CHILDREN  UNDERGOES BIOTRANSFORMATION IN LIVER BY CONJUGATION WITH GLUCURONIC ACID.  TOTAL DOSE IN HEALTHY ADULT SHOULD NOT EXCEED 2mg/Kg (0.9mg/lb)NOT TO EXCEED 225 mg WITH 1:200,000 EPINEPHRINE OR 175 mg WITHOUT A VASOCONSTRICTOR  TOTAL DOSE MAY BE REPEATED UPTO ONCE EVERY 3 HOURS NOT TO EXCEED 400 mg IN 24 HOURS
  48. 48. ETIDOCAINE  WHITE CRYSTALLINE POWDER FREELY SOLUBLE IN 95% ETHANAL AND WATER  PH IS 3-5 AND pKa IS 7.7  AMIDE DERIVATIVE, STRUCTURALLY SIMILAR TO LIDOCAINE, WITH A PROPYL FOR AN ETHYL GROUP AT THE AMINE END AND THE ADDITION OF AN ETHYL GROUP AT THE ALPHA CARBON IN THE INTERMEDIATE CHAIN  PRESENTLY NOT AVAILABLE IN A DENTAL CARTRIDGE  IT SUPPLIED IN 30 AND 50 ml VIALS CONTAINING 0.5% OR 1% SOLUTION OF ETIDOCAINE WITHOUT A VASOCONSTRICTOR OR WITH 1:200,000 EPINEPHRINE
  49. 49. • A 20ml VIAL CONTAINING 1.5% ETIDOCAINE WITH 1:200,000 EPINEPHRINE IS ALSO AVAILABLE • 50 FOLD INCREASE IN OIL WATER PARTITION COEFFICIENT AND ALMOST 2 TIMES PROTEIN BINDING CHARACTERISTICS • FASTER ONSET AND LONGER DURATION • 4 TIMES INCREASE IN ANESTHETIC ACTIVITY AND 2 TIMES LONGER DURATION OF ACTION THAN LIDOCAINE • NOT ADMINISTERED TO CHILDREN
  50. 50.  TWICE AS TOXIC AS LIDOCAINE  TOTAL DOSE SHOULD NOT EXCEED 4mg/Kg (1.8mg/lb) TO A MAXIMUM OF 300 mg WHEN USED WITHOUT A VASOCONSTRICTOR  4.4mg/Kg (2mg/lb) TO A MAXIMUM OF 400mg WHEN COMBINED WITH 1:200,000 EPINEPHRINE  INCREMENTAL DOSE MAY BE REPEATED EVERY 2 TO 3 HOURS
  51. 51. TOPICAL ANESTHETICS  DIRECT APPLICATION TO ABRADED SKIN OR TO THE MUCOUS MEMBRANE SURFACE  PORELY SOLUBLE IN WATER AND DO NOT FORM SOLUBLE ACID SALTS  MOST COMMON EXCEPTIONS ARE LIDOCAINE AND TETRACAINE  LIDOCAINE 5% OR 10%  TETRACAINE 1% OR 2%  HIGHER CONCENTRATIONS ARE REQUIRED FOR DIFFUSION THROUGH MUCOUS MEMBRAN
  52. 52. • IN ADDITION THE MOST COMMONLY USED TOPICAL ANESTHETICS ARE BENZOCAINE (ETHYL AMINOBENZOATE) AND BENZYL ALCOHOL • WATER INSOLUBLE TOPICAL ANESTHETICS • SOLUBLE IN VEHICALS SUCH AS ALCOHOL, POLYETHYLENE GLYCOL, PROPYLENE GLYCOL OR CARBOXYMETHYLCELLULOSE THAT MAKES THEM AMENABLE TO SURFACE APPLICATION • POORLY ABSORBED AND SYSTEMIC TOXICITY VIRTUALLY UNKNOWN
  53. 53. BENZOCAINE  CLOSELY RELATED TO PROCAINE  ESTER OF AMINOBENZOIC ACID  NO BASIC NITROGEN GROUP, HENCE UNABLE TO FORM SOLUBLE ANESTHETIC SALTS  HURRICAINE CONTAINS BENZOCAINE  IRRITATING IF INJECTED IN TO TISSUE  CAN PRODUCE TOXIC SYMPTOMS IF ABSORBED IN SUFFICIENT QUANTITIES
  54. 54. LIDOCAINE  AVAILABLE IN TWO FORMS: LIDOCAINE BASE LIDOCAINE HYDROCHLORIDE  LIDOCAINE BASE  INSOLUBLE IN WATER  5% CONCENTRATION  EXCELLENT SURFACE ANESTHESIA WITHIN 15 SECONDS OF APPLICATION  SINGLE APPLICATION HAS A DURATION OF ABOUT 30 MINUTES  POORLY ABSORBED, SYSTEMIC TOXICITY IS NEGLIGIBLE  10% LIDOCAINE BASE IN AN AEROSOL SPRAY WITH A METERED DOSE VALVE DISCHARGES 10mg PER SPRAY ALSO
  55. 55. WATER SOLUBLE TOPICAL ANESTHETICS  PRIMARY DISADVANTAGE: RAPID ABSORPTION IN TO BLOOD STREAM  BENZYL ALCOHOL  AROMATIC ALCOHOL SOLUBLE IN WATER  VERY IRRITATING ON INJECTING INTO THE TISSUES  4% TO 10% SOLUTIONS  SHORT ACTING  LESS TOXIC THAN ETHYL AMINOBENZOATE
  56. 56. TETRACAINE HYDROCHLORIDE  VERY POTENT  HIGHLY WATER SOLUBLE  ONSET OF ACTION IS SLOW BUT DURATION IS RELATIVELY LONG LASTING (45 MINUTES TO 1 HOUR)  FREQUENTLY COMBINED WITH BENZOCAINE, AN AGENT OF RAPID ONSET AND BRIEF DURATION  A MIXTURE OF BENZOCAINE 14%, BUTAMBEN 2% AND TETRACAINE 2% DISSOLVED IN DIPROPYLENE GLYCOL UNDER THE NAME CETACAINE IS EXTENSIVELY USED  MAXIMUM DOSE: 20 mg OR 1 ml OF 2% SOLUTION
  57. 57. LIDOCAINE HYDROCHLORIDE  2% OR 4% CONCENTRATION  MAXIMUM RECOMMENDED DOSE IS 200mg  WHEN APPLIED BY MEANS OF COTTON APPLICATORS THE SUGGESTED MAXIMUM DOSE IS 1 TO 5 ML (40 TO 200MG) OR 0.6 TO 3 mg/Kg (0.3 TO 1.5 mg/lb) NOT TO EXCEED 300mg OR 4.5mg/kg
  58. 58. VASOCONSTRICTORS
  59. 59.  THE VASOCONSTICORS COMMONLY USED IN DENTAL LOCAL ANESTHETIC SOLUTIONS CAN BE DIVIDED INTO THE FOLLOWING 3 GROUPS 1. PYROCATECHINE DERIVATIVES- EPINEPHRINE AND NOREPINEPHRINE 2. BENZOL DERIVATIVE- LEVONORDEFRIN 3. PHENOL DERIVATIVE- PHENYLEPHRINE
  60. 60. MODE OF ACTION SYMPATHOMIMETICS AMINES ACT BY 1. ATTACHING TO AND DIRECTLY STIMULATING ADRENERGIC RECEPTORS 2. ACTING INDIRECTLY BY PROVOKING THE RELEASE OF ENDOGENOUS CATECHOLAMINES 3. A COMBINATION OF DIRECT AND INDIRECT ACTION ALL VASOCONSTRICTORS USED IN CONJUNCTION WITH LOCAL ANESTHETICS ARE DIRECTLY ACTING AGENTS
  61. 61. EPINEPHRINE  LEVOROTATORY ALKALOID SECRETED BY ADRENAL MEDULLA  HIGHLY SOLUBLE IN WATER  MOST POTENT VASOCONSTRICTOR USED  USED AS STANDARD OF COMPARISON  HAS A PRESSOR POTENCY OF ONE  CONCENTRATIONS FROM 1:50,000 TO 1:250,000 ARE USED
  62. 62. CVS: BETA1 STIMULATION RESULTS IN AN INCREASE IN HEART RATE (POSITIVE CHRONOTROPIC EFFECT) INCREASE IN STROKE VOLUME, CARDIAC OUTPUT AND OXYGEN CONSUMPTION INCREASED IRRITABILITY OF MYOCARDIUM- PREMATURE VENTRICULAR CONTRACTIONS AND TACHYCARDIAS OTHER EFFECTS: INCREASED BLOOD GLUCOSE LEVELS, INCREASED GLYCOGENOLYSIS AND PUPILLARY DILATION
  63. 63. NOREPINEPHRINE  MAJOR PRESSOR AMINE FOUND IN THE POSTGANGLIONIC ADRENERGIC NERVE  WHITE CRYSTALLINE SALT, FREELY SOLUBLE IN WATER WITH A PH OF 3.4  IT HAS NO RADICAL ON THE AMINO GROUP  ACTS PREDOMINANTLY ON THE ALPHA RECEPTOR SITE  DOSE SHOULD NOT EXCEED 0.34mg OR 10ml OF SOLUTION CONTAINING 1:30,000
  64. 64. LEVONORDEFRIN  IT IS ONE FIFTH AS ACTIVE AS EPINEPHINE  LOWER SYSTEMIC TOXICITY  IT ACTS DIRECTLY AND ALMOST EXCLUSIVELY ON THE ALPHA RECPTOR SITES  DOSE: WHEN 1:10,000 CONCENTRATION IS USED IT SHOULD BE LIMITED TO A TOTAL DOSE OF 1mg  PATIENTS WITH CARDIAC CONDITIONS ITS USE SHOULD BE LIMITED TO A MAXIMUM OF 0.4mg
  65. 65. PHENYLEPHRINE  SIMILAR TO EPINEPHRINE BUT DIFFERING STRUCTURALLY .  IT HAS ONLY ONE HYDROXYL GROUP ON THE BENZENE RING  IT IS THE MOST STABLE AND WEAKEST OF ALL VASOCONSTRICTORS AND LONG LASTING  USED IN CONCENTRATIONS 10 TO 20 TIMES THOSE OF EPINEPHRINE: 1:2,500  IT IS A PURE ALPHA RECEPTOR AGONIST  DOSE: 1:2,500 LIMITED TO 4mg AT ONE TIME  IN PATIENTS WITH CARDIAC CONDITIONS : REDUCED TO 1.6 mg
  66. 66. TERMINATION OF ACTION AND POTENTIAL DRUG INTERACTION  TRICYCLIC ANTIDEPRESSANTS INTERFERE WITH THE REUPTAKE MECHANISM  DEACTIVATION BY EXTRANEURONAL ENZYME (CATECHOL- O-METHYL TRANSFERASE)  UPTAKE BY BLOOD SYSTEM  INTRANEURONAL ENZYME DESTRUCTION (MONOAMINO OXIDASE)  MAO I INHIBITOR  ALPHA ADRENERGIC BLOCKERS: PHENOTHIAZINE  EPINEPHRINE REVERSAL EFFECT  BETA ADRENERGIC BLOCKERS (PROPRANOLOL, INDERAL)
  67. 67. SELECTION OF VASOCONSTRICTORS 1. DURATION OF DESIRED EFFECT 2. PHYSICAL CONDITION OF THE PATIENT 3. DESIRE TO PRODUCE HEMOSTASIS 4. CONCURRENT MEDICATION
  68. 68. Properties of ideal LA  Reversible action.  Non-irritant.  No allergic reaction.  No systemic toxicity.  Rapid onset of action.  Sufficient duration of action.  Potent.  Stable in solutions.  Not interfere with healing of tissue.  Have a vasoconstrictor action or compatible with VC.  Not expensive
  69. 69. CONCLUSION
  70. 70. Mechanism of action - Inhibiting excitation of nerve endings or blocking conduction in peripheral nerves. Binding to and inactivating sodium channels. - Local Anaesthetics are alkaloid bases that are combined with acids, usually hydrochloric, to form water soluble salts. All anaesthetic salts are formed by a combination of weak base and a strong acid. The salts are used because they are stable and soluble in water; water solubility isnecessary for their diffusion through interstitial fluids to the nerve fibers.
  71. 71. - Sodium influx through these channels is necessary for the depolarization of nerve cell membranes and subsequent propagation of impulses along the course of the nerve. - when a nerve loses depolarization and capacity to propagate an impulse, the individual loses sensation in the area supplied by the nerve
  72. 72. - block nerve fiber conduction by acting on nerve membranes - inhibit sodium ion activity - blocks depolarization--> blocks nerve conduction
  73. 73.  When the influx of sodium is interrupted, an action potential cannot arise and signal conduction is inhibited. LA drugs bind more readily to sodium channels in activated state, thus onset of neuronal blockade is faster in neurons that are rapidly firing. This is referred to as state dependent blockade.

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