Local anesthesia
Lecture 3Composition of local anesthetic solution
Local anesthetic agent Vasoconstrictor Preservative Reducing agent Fungicidal agent Sodium chloride and distilled waterOther agents: TCAD Tramadol Diphenhydramine meteclopromide neosaxitoxin
Local anesthetic agentAmide Lidocaine Mepivicaine Prilocaine Articaine Bupivicaine Etidocaine
Ester Cocaine Procaine Propoxycaine
LidocaineMost common agent Discovered in 1948 ( first of amide group) Regarded as the standard Minimal allergisity Have topical anesthetic activity Vasodilating activity PKa =7.9
Onset of action = 2-3 min Duration = 60 min (pulpal) and 60-120 min (soft tissue) Maximum recommended dose (MRD)= 4.4mg/kg =300 mg
Metabolism and safety
Lidocaine metabolized in liver and excreted in urine (10% unchanged completely)? Contraindicated in end stage liver disease On CNS large dose cause initial stimulation followed by depression ( anticonvulsant effect) On CVS large dose cause myocardial depression ( used in ventricular tachycardia)back
Maximum dose calculation
Available concentration =2% =2gm in each 100 ml /100 →→→→0.02gm/ml = 20 mg/ml*2 ml/dental cartridge =40 mg /dental cartridge300 /40 = 7.5 dental cartridge (MRD)back
MepivicaineSame potency to lidocaine Similar to lidocaine in metabolism and excretion Same onset slight extended duration (weak vasodilatation) PKa =7.6
Less toxic than lidocaine Used for child and geriatric patient when vasoconstrictor contraindicatedMRD =4.4 mg/Kg= 300mg 2% → 7.5 cartridge3% → 5 cartridge
Prilocaine (citanest)
Same potency to lidocaineLess toxicityLess vasoldilating activity PKa =7.9MRD =6mg/kg3% → ?? cartridge4% → ??? cartridge
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Prilocaine (citanest)Metabolism occur mostly in liver into orthotolidine which can cause methemoglobulinemia in susceptible individual (patient with hemolytic anemia) if used in large dose → poor oxygen carrying capacity resulting in cyanosisClinically patient may have cyanosis in the lip, mucous membrane and skin. Patient may also have respiratory distress in severe casesTreatment by methyline blue 1% injection 1-2 mg/kg IV/5min
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ArticaineSlightly more potent than lidocaineSimilar toxicity, and vasodilating activitySome literature present a cross allergisity with sulfate so it is best to be avoided in patient allergic to sulfonamide MRD =7mg/kg 4% → 7 cartridgeSimilar to prilocaine in producing methemoglbulinemia
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BupivicaineFour times more potent than lidocaine and 4 times less toxic Slower onset (5-10 min) and extended duration lasting for 90-180 minMRD =1.3mg/kg 0.5% → 10 cartridge
Dental Indication Prolonged dental procedure Expected post operative pain Contraindication Child and mentally retarded patient
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EtidocaineSimilar to bupivicaine except:More toxic than lidocaineMRD= 8mg /kg available in1.5% → 13 cartridge In general surgery both indicated in prolonged procedure when uses of vasoconstrictor is contraindicated systemically or locally
Ropivicaine
A newer long acting local anethesia as an isomer of bupivicaine with minimum toxicity and more effectivenessLocal anesthetic agent
Amide Lidocaine Mepivicaine Prilocaine Articaine Bupivicaine EtidocaineEster Cocaine Procaine Propoxycaine
backCocaine
Oldest anesthetic agent used since 18th century It is the only agent having a vasoconstrictor activity( sympathomimatic activity) and can be used topically because it is rapidly absorbed through mucous membrane It has liability for dependence which makes its uses very limited
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ProcaineHas 50% potency and toxicity than lidocaine It has prominent vasodilating activity which reduce its duration PKa =9.1 (slow onset) MRD =1000mg
Its hydrolyses occurs in plasma by enzyme pseudocholine esterase High incidence of allergisity
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PropoxycaineMore potent and more toxic than lidocaine Has rapid onset and adequate duration It is available in combination form with procaine to reduce toxicity 0.4% propoxycaine + 2% procaine =24mg/ml MRD =400 mg It is indicated only in patient allergic to amide form of local anesthesia
H W
MD calculation in prilocaine Other agents having local anesthetic properties WriteAbout EMLA, carbonated local anesthesia
Composition of local anesthetic solution
Local anesthetic agent Vasoconstrictor Preservative Reducing agent Fungicidal agent Sodium chloride and distilled waterVasoconstrictor
Advantages of vasoconstrictor in combination with local anesthesia: Reduce blood flow thus reduce bleeding Reduce local anesthetic absorption and toxicity (reduce systemic effect) Increase duration and depth of anesthesiaTypes of vasoconstrictor
Adrenergic agonist agent VasopressinAdrenergic agonist agent (sympathomimetic agent) - catecholamine
Mode of action: Direct (binding) Indirect (displacing) Mixed actionSympathetic receptors:1 vasoconstriction2 Reuptake1 Cardiac stimulation2 Vasodilatation
-
-
+
+
Phenylphrine
+
++
++
+
Levonordephrine
-
-
++
++
Nor - adrenaline
++
++
++
++
Adrenaline
2 1 2 1
Affinity of adrenergic agents on receptors
OHCH
CH
1
NH
Epinephrine
Levonordefrin
Norepinephrine
CH
H
H
3
H
CH
H
3
1
2
HO
2
HO
Adrenaline
Synthetic or natural abstract from adrenal medulla . It is the most common and potent vasoconstrictor. Concentration: Expressed in ratio gm: ml / 1: 100000 Meaning 1 gm in 100000 mlConcentration
1:100000 means: =1 gm in 100000 ml =1000 mg in 100000 ml= 0.01 mg /mlIn single dental cartridge (1.8 ml)= 0.018 mg =18 g (microgram)Adrenaline availability (concentration)
1:1000 (alone) is used for control of bleeding? contraindicated in arterial bleeding- Rebound bleeding 1:50000 for surgery where hemostasis is necessary 1:80000 and 1:100000 commonly used concentration 1:200000 low concentration used for medically compromised patient (vasoconstrictor contraindicated) and where hemostasis is of little importance15
1:20000
1
levonordephrine
5
1:2500
4
Phenylphrine
25
1:30000
0.34
Nor - adrenaline
100
0.2
Adrenaline
Potency
Available concentration
MRD (mg)
Maximum recommended dose (MRD)
Other adrenergic agonist vasoconstrictorNor-adrenaline and phenylphrine have prominent alpha activity comparing to beta activity which may result in severe vasoconstriction (increase blood pressure) and ischemia. It is contraindicated in patients with cardiac problem. It is contraindicated in terminal extremities
MAO
MAO
Receptor
a
Extraneuronal
tissues
Renal
excretion
[ COMT ]
[ COMT]
Adrenergic
nerve terminal
Injected drug
COMT: Catechol-O-methyltransferase MAO: monoamine oxidase
Metabolism of catecholamines
Side effects and overdoseCNS: Fear apprehension palpitationCVS: Cardiac stimulant effects , increase blood pressure and rebound bleeding at prolonged dental procedure. Causes of rebound bleeding:Adrenaline selectivity on receptor:Low concentration effectHigh concentration effect
Limitation of adrenergic vasoconstrictor
Precautions/contraindications Uncontrolled Cardiovascular disease Uncontrolled thyrotoxic goiter Drug interactions Tricyclic antidepressants General anesthetics Adrenergic antagonists COMT inhibitors Not MAO inhibitorsVasoconstrictors (epinephrine, Levonordefrin) with Tricyclic antidepressants (imipramine, desipramine)
Hypertensive and/or cardiac reactions are more likely. Use epinephrine cautiously; avoid Levonordefrin.
Vasoconstrictors (epinephrine, Levonordefrin) with
Vasoconstrictors (epinephrine, Levonordefrin) with
Nonselective beta blockers (Propranolol, Nadolol)Hypertensive and/or cardiac reactions are more likely. Use cautiously.
Vasoconstrictors (Epinephrine, Levonordefrin) withCOMT inhibitors (Tolcapone, Entacapone) Hypertensive and/or cardiac reactions are more likely. Use cautiously.
Consideration
MRD for cardiovascular disease patient = 0.04 mg of adrenaline = 2 dental cartridge of 2ml 1:100000 concentration adrenaline Controversy still exists on using adrenaline in controlled cardiovascular diseased patient. Explain why?Uses of small amount available in dental cartridge is better than exposing the patient to failure anesthesia which produce pain and bleeding that can stimulate fear and increase intrinsic adrenaline that may have more dangerous effect than extrinsic adrenaline
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Vasopressin (Felypressin)Synthetic analogue of posterior pituitary hormone (Octopressin) Act on V1 receptor that is found on venous site of microcirculation It posses mild hemostatic effect and used only when other vasoconstrictor contraindicated Available concentration = 0.03 IU/ml in combination with prilocaine 2% or 3% MRD= 0.27 IU
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PreservativeMaintains sterility of the solution Caprylhydrocuprienotoxin used for this purpose Methylparaben used in the past but nowadays omitted ?
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Reducing agent (in vasoconstrictor containing solution)Antioxidant (reducing agent) used to prevent oxidation of vasoconstrictor that may deteriorate on exposure to sunlight (brown discoloration) Sodium metabisulfite used for this purpose On exposure to oxygen it will diffuse through the rubber of the cartridge where sodium metabisulfite will be converted to sodium metabisulfate (oxidized) Oxidized instead of vasoconstrictor Why is an old solution more acidic? Painful ? Irritant?
Fungicide Thymol Sodium chloride and distilled water (ringers solution) For isotonicity of injected solution to reduce edema and discomfort on injection