2010 Anesthesia Lectue - Pharmacology of Local Anesthetics
Post on 17-Jul-2015
64 Views
Preview:
Transcript
Pharmacology of Local Anesthesia(Mode of Action, dosage and Available Forms)Dr. Ana Maria Ospina. Department of Oral and Maxillofacial Surgery NOVA Southeastern University
Local AnesthesiaA 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, without inducing a loss of consciousness.
Depressant
effect on excitable membranes
L.A. are chemicals that reversible block action potentials in excitable membranes. All drugs regardless of the route of administration must enter into the circulatory system before they begin to exert a clinical action; L.A. however cease to provide a clinical effect when they are absorb from the site of administration into the circulation.
All local anesthetics produce a peripheral vasodilation local blood flow rate of absorption blood levels depth and duration bleeding
Pharmacological Characteristics
Three components common to LAs:
Aromatic Lipophilic Group (Hydrophobic). Intermediate chain > Either ester or amide. Hydrophilic Amino Group.
Esters of benzoic acid:Butacaine Cocaine Ethyl aminobenzoate (benzocaine) Hexylcaine Piperocaine Tetracaine
Esters paraaminobenzoic acid:Chloroprocaine Procaine Propoxycaine
Amide Articaine Bupivacaine Dibucaine Etidocaine Lidocaine Mepivacaine Prilocaine Ropivacaine Quinoline Centbucridine (
Composed ofEsters:
Amides:
Cocaine Ethyl Aminobenzoate (Benzocaine) Tetracaine Procaine Propoxycaine
Lidocaine (Xylocaine) Mepivacaine (Carbocaine) Prilocaine (Citanest) Bupivacaine (Marcaine) Etidocaine (Duranest) Articaine (Septocaine)
UPTAKE of local anesthetic molecules
Factors that influence the uptake:
Access of the agent: Topical
application. Injection.
Closeness of the solution to the nerve. Diameter of the nerve. Vascularity Vasoactivity and concentration
Blood level is influenced by
Rate of absorption Rate at which the drug is absorbed into cardiovascular system
Blood level is influenced by
Rate of distribution (From vascular compartment to tissues, more rapid in healthy patients)
Blood level is influenced byDISTRIBUTIONThroughout the body to all tissues... Highly perfused organs, higher blood levels
Blood level is influenced by
Elimination (metabolic or excretory)
Time to Achieve Peak Blood LevelRouteIntravenous
Time1 min
IntramuscularTopical Subcutaneous
5-10 min5 min 30-90 min
Metabolism Overall
toxicity depends on a balance between its rate of absorption and its rate of removal
Metabolism (Biotransformation)
EsterHydrolyzed by the enzyme
Pseudocholinesterase
AmideMetabolism occurs in the liver.
Contraindications
Absolute: under no circumstance should the drug be administered Relative: May be administered after weighing the risk and benefits
Contraindications(relative vs. absolute) For EstersAtypical form of Pseudocholinesterase. (1/2800 person) PABA allergy Significant liver dysfunction, or Heart failure. ASA IV Allergy
For Amides
Contraindications for Local Anesthetics
Doubt: medical consultation to be sought
The biotransformation products of some LAs can cause certain clinical activity if they are permitted to accumulate in the blood. E.g., large doses of PrilocaineOrthotoluidine Methemoglobin Methemoglobinemia
Methemoglobinemia
Blood appears chocolate brown Deficient delivery Oxygen to tissues Cyanosis like state Respiratory depression Syncope Treatment: IV Methylene blue
Duration of ActionFactors:
Individual response to the drug. Accuracy in deposition of the local anesthetic. Anatomical variation. Status of the tissues at the site of drug deposition. Type of L.A. administered. Vasoconstrictor.
Excretion
Occurs mainly in the kidneys. 12-24 hours. Patients with significant renal impairment
Components for a cartridge of local anesthesia:
Each cartridge has 1.7 ml solution Local Anesthetic Agent. Sodium Chloride. (Alkalinizing Agent) Vasoconstrictor (and Antioxidant) Sterile water. (diluent)
Local Anesthetics Available in United States(Cartridges)Local Anesthetic + Vasoconstrictor Articaine 4% + epinephrine 1:200,000 1:100.000 Bupivacaine 0.5% + epinephrine 1:200,000
Duration of Action Intermediate ( ~ 60 min) Long (more than 90 min) Short (less than 30 min) Intermediate Intermediate
Lidocaine 2% 2% + epinephrine 1:50,000 2% + epinephrine 1:100,000Mepivacaine 3% 3% + levonerphrine 1:20.000 Prilocaine 4% 4% + epinephrine 1:200,000
Short IntermediateShort Intermediate
Local Anesthetics Available in United States (Other presentations)Local Anesthetic
Lidocaine (2%, 2.5%, 4%, 5%) /Prilocaine 2.5%Benzocaine 20%, 18% and 16%Benzocaine 14% + Butamben 2%
GelSpray
Gel Tetracaine 2% Gel Bupivacaine 0.5%, 0.25% Mepivacaine 1%, 2% Lidocaine 1%, 2%
Multi vials
Dosages
Maximum Recommended Dosages (MRDs) of Local Anesthetics Available in North America
MRD
The least concentrate solution that produce effective pain control should be used
Recommended Maximum Local Anesthetic Doses Hupp et al.
Cartridge1.7 ml of local anesthetic solution (USA) How to calculate # of mg of LA in a cartridge? By multiplying: Percent Concentration x 1.7 ml Example: Lidocaine 2% 2 % = 20 mg/ml 20 mg/ml x 1.7 (ml) = 34 mg of anesthetic agent in the cartridge.
Cartridge
Lidocaine Mepivacaine Articaine Bupivacaine
2% 3% 4% 0.5%
2 % = 20 mg/ml 3 % = 30 mg/ml 4 % = 40 mg/ml 0.5 % = 5 mg/ml
Case 122 Years old, healthy, 70 kg.Lidocaine 2 % = 34 mg in 1 cartridge (20mg/ml x 1.7 ml = 34 mg ) Maximum # mg / kg = 5 mg /kg
70 kg x 5 mg/kg = 350 mg 350/34 = 10 cartridges
Case 26 years old, healthy, 28 kgMepivacaine 3 % = 51 mg in 1 cartridge (30mg/ml x 1.7ml = 51 mg) Maximum = 5 mg/kg
28 kg x 5 mg/kg = 140mg / 51mg = 2.7 cartridges ofMepivacaine
Case 355 years old, healthy, 90 kgArticaine 4 % = 68 mg in 1 cartridge (40mg/ml x 1.7ml = 68 mg) Maximum = 7.0 mg/kg
90 kg x 7.0mg/kg = 630mg / 68mg =9.2 cartridges
Case 455 years old, healthy, 90 kgBupivacaine 0.5 % =8.5 mg in 1 cartridge (5mg/ml x 1.7ml = 8.5 mg) Maximum = 1.5 mg/kg
90 kg x 1.5mg/kg = 135mg / 8.5mg = 15 cartridges
Overdose
Administration of too large local anesthetic dose in relation to the age and weight of the patient. Overwhelming majority of cases: in children.
* All L.A. readily cross
blood-brain barrier plancenta
CNS: Toxic: Tonic-clonic convulsion CVS: Toxic: Cardiac arrest
Respiratory: Toxic: Respiratory arrest
Nothing that is done for a patient is of greater importance than the administration of a drug that prevents pain during treatment
Bibliography
Handbook of Local Anesthesia , Fifth Edition Stanley F. Malamed (Vital Source)
Thanks for your Attention ...!
top related