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98 Cards in this Set
- Front
- Back
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What is the action of a local anaesthetic?
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-block sensory impulses from the periphery to the CNS
-ABOLISH SENSATION in a ltd area of the body -at higher doses may abolish mtr activity |
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Local anesthetics cause loss of consciousness. True or false?
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FALSE
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What is the basic structure of a local anaesthetic?
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-lipophilic group (aromatic ring
-intermediate chain (ester or amide) ioninzable group (tertiary amine) |
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What r the two groups of anaesthetics structurally?
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-intermediate chain is an
1-ESTER 2-AMIDE |
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Ester prototype local anaesthetic?
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Procaine
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Amide prototype local anaesthetic?
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Lidocaine
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Name the esters (local anaesthetics)?
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Cocaine
Benzocaine(not popular) Procaine Tetracaine |
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Which group of local anesthetic is more prone to hydrolysis?
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Esters (e.g procaine)
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Which group of local aesthetic has a short duration of action?
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Esters
This is due to them being more prone to hydrolysis |
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Local anaesthetics are bases or acids?
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Weak bases
pK 8-9 They are marketed as HYDOCHLORIDE salts which are mildy acidic |
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What form will the local anaesthetic be in the body
-anionic or cation? |
Cationic
More are in the protonated form due to the body pH being lower than the pK of the drug. |
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Which form of the drug is most active at the receptor site?
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Cationic/Protonated form
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What is the importance of the uncharged form of the drug?
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The uncharged form is lipophillic and is important for penetration of biologic membranes.
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What procedures are used to keep the local anesthetic at the nerve?
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The preparations contain a vasoconstrictor.
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What is the common vasoconstrictor used?
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Epinephrine
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Which local anesthetic does not need a vasoconstrictor?
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Cocaine - It constricts blood vessesl on its own
Prilocaine - it causes little vasodilation and does not need a vasoconstrictor |
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How does cocaine cause vasoconstriction?
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It decreses the reuptake of NE at the presynaptic cleft.
More NE causes constrction of blood vessels. |
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What other action does the vasoconstrictor allow?
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-decreases sytemic absorption of the drug
by decreasing blood flow -this enhances neuronal uptake of the drug -reduces sytemic toxic effects -prolong the period of anaesthesia |
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How does epinephrine act in spinal anesthesia?
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Epi acts on alpha2 receptors in the presynaptic neuron inhibiting release of SUBSTANCE P
- |
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What is the added effect of epinephrine in a spinal anesthesia?
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Decreased pain perception by inhibiting Substance P
Recognition of this has led to the use of other alpha 2 agonists CLONIDINE and DEXMEDETOMIDINE |
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What are the adverse effects of the vasoconstrictor?.
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-delayed wound healing
-tissue edema -necorsis |
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How are the esters of local anesthetics metabolized?
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Metabolism by
-TISSUE esterases and PLASMA esterases (pseudocholinesterases) |
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Which group of local anesthetics are degraded using liver cytP450 enzymes
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AMIDES
this also contributes to the longer duration of action |
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What is the general MOA of local anesthetics?
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They block voltage gated sodium(Na+) channels that conduct the axn potential along the neuron
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What 2 factors are the blockade of sodium channels by local anesthetics dependent on?
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VOLTAGE dependent
TIME dependent |
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Where on the receptor does the local anesthetics bind?
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They bind the receptor from the inside of the cell (near the intracellular end)
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How does the drug bind the receptor intracellulary?
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1. the uncharged form is lipophillic and penetates the membrane of the neuron
2. the uncharged form becomes protonated inside the cell 3. the protonated form binds to the receptor |
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Sufficient concentration of the local anesthetic on a nerve fiber would cause?
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action potential is abolished
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What are the steps of local anesthetics to abolish the action potential in a nerve fibre?
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1.The treshold for excitation increases
2. the impulse conduction slows 3. the rate of rise of the action potential declines 4. the amplitude of the axn potential decreases 5.Finally the ability to generate an action potential is abolished |
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What is the benefit of a smaller and more lipophillic molecule of the drug?
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the onset of action is faster
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The potency of a local anesthetic is related to?
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the LIPOPHILICITY
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Which agents are more liposoluble?
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Bupivacaine
Ropivacaine Tetracaine |
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Which local anesthetic agents are more POTENT?
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Bupivacaine
Ropivacaine Tetracaine |
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Which local anesthetic agents have a LONGER duration of action
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Bupivacaine
Ropivacaine Tetracaine |
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What characterstic is used when chosing a local anesthetic for a specific procedure?
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The duration of action requied
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Which 2 drugs are SHORT acting?
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Procaine and
Chloro-procaine |
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Which 3 drugs are INTERMEDIATE acting?
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Lidocaine
Mepivacaine Prilocaine |
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Which 4 drugs are LONG acting?
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Bupivacaine
Etidocaine Tetracaine Ropivacaine |
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Can local anesthetics cause toxic effects?
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YES
-they are absorbed from the site of administration eventually -blood levels can rise too high causing effects on several organ systems |
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What systems are affected by local anesthetics?
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CNS
peripheral nervous system cardio-vascular system -blood (Hb) -Skin |
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Adverse effects of CNS stimulation causes?
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-restlessness
-tremor that can progress to clonic convulsions -CNS depression follows |
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Death from a local anestehtic is due to?
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Respiratory failure
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Excessive blood leves of a local anesthetic can cause?
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CONVULSIONS
(more serious toxic reaction) |
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What PREMEDICATION is given to prevent seizures, when LARGE doses of a local anesthetic must be used
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BENZODIAZEPINES
provides significant prophylaxis against seizures |
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What is the adverse effect of a local anesthetic on the Peripheral Vascular System?
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NEURO-TOXICITY
at excessively high conc, ALL local anesthetics are toxic to nerve tissue |
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What is the A/E of local anesthetics on the Cardio-Vascular system?
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(due to blockage of sodium channels)
-Depresses cardiac pacemaker ; activity, excitability and conduction -depress strength of cardiac contraction (EXCEPT cocaine) -cause arteriolar dilation and HYPOtension (EXCEPT cocaine) |
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Which local anesthetic is MORE cardiotoxic?
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BUPIVACAINE
(not as popular because of this) |
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What is the effect of Cocaine on the Cardio-Vascular system?
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-vasoconstriction
-HYPERtension -Cardiac arrythmias The vasoconstriction can lead to ISCHEMIA and in chronic abusers it causes ulcerations of mucous membranes and damage to the nasal septum |
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Which local anesthetic causes production of MET-hemoglobin?
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PRILOCAINE
(large doses used during regional anesthesia) MetHb causes decompensation in patients with cardiac or pulmonary disease and require immediate treatment |
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Name the metabolite of PRILOCAINE?
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o-toluidine
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What causes the production of MET-hemoglobin in blood?
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accumulation of oxidizing agent O-TOLUIDINE
(metabolite of PROCAINE) Treatment is METHYLENE BLUE given IV to convert MetHb to Hb |
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Which type of local anesthetics are metabolized to PABA?
p-aminobenzoic acid |
The ESTER types
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What causes the allergic reactions when using local anesthetics?
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PABA-metabolites of ester type anesthetics
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Are amide type local anesthetic metabolized to PABA?
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NO
so allergic reactions to these amide types are rare |
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What is the management of the A/E on the Cardio-Vascular system?
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-IV fluids
-vasopressors when appropriate (like ephedrine-stimulates myocardium) -Hypotention treatment: vasoconstrictors IV or IM |
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What is the management of the A/E on the CNS?
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Convulsions are controlled with
-oxygen -IV diazepam (benzodiazepines) or -ultra-short acting barbituates or -succynyl choline - |
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What is the management of the A/E on the skin?
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-mild cutaneous reaction- DIPHENHYDRAMINE
-more serious reaction- SC epinephrine |
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Which drug use is contraindicated with Procaine?
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Sulfonomide drugs
Procaine produces PABA which causes inhibition of the action of sulfonamides |
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What is the MOA of sulfas?
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they block the conversion of PABA+Pteridine to Dihydropteric acid
(inhibits enzyme Dihydropterate synthetase) |
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What are the properties of PROCAINE?
prototype ester-linked local anesthetic |
short acting
low hydrophobicity low potency -degraded by pseudoesterases -metabolites excreted in urine |
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What is the primary use of procaine?
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-inflitration anesthetics
-DENTAL procedures -diagnostic nerve blocks (ocassionally) |
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Which anesthetic is popular in obstetrics?
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Short acting homolog of Procaine
2- CHLORO-procaine |
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What r the properties of Tetracaine?
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-long acting
-HIGHLY potent -high hydrophobicity (so long duration of action) -slow metabolism (despite the ester linkage it is relesed slowly from the tissues into the blood) |
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What are the main uses of Tetracaine?
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Spinal and topical anesthesia
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What r the properties of Cocaine?
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-ONLY naturally occuring local anes.
-MEDIUM potency -medium duration of action -vasoconstrictive axn due to inhibition of NE reuptake |
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What properties of Cocaine contribute to its cardiotoxic potential and euphoric effect?
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inhibition of NE reuptake
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What is the primary use of Cocaine as a local anesthetic?
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Ophthalmic anesthesia
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What is another primary use of Cocaine as a local anesthetic?
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Part of a Topical anesthetic-TAC
- TAC -Tetracaine, Adrenaline, cocaine -mixture sometimes used before suturing small cuts |
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What is the new alternative to TAC?
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EMLA cream (Eutectic mixture of Local anesthetic)
This is an emulsion in which the oil phase is a mixture of Lidocaine and Prilocaine 1:1 by weight NB. Eutectic means they melt at a temp lower that each other |
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Why was EMLA formulated?
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-this was because of concern about coacaine toxicity and/or addiction
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What properties does EMLA possess?
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The formulation allows effective skin penetration than other anesthetic creams
(good for use in children afraid of needles) |
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What r the properties of Lidocaine?
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-moderate hydrophobicity
-moderate potency -RAPID onset of action -Medium duration of action -LOW pKa |
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What advantage does Lidocaine possess with its low pKa?
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a large fraction is present in the non-ionized form at physiologic pH
-FAST diffusion via membranes (more than others) -Rapid block of nerve |
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Which local anesthetic is the MOST popular?
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Lidocaine
A/E includes drowsines, tinnitus, twitching and even seizures |
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What are the uses of Lidocaine as a local anesthetic?
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-infiltration anesthesia
-Peripheral nerve block -epidural, spinal and topical anesthesia |
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What class of antiarrythmic drug does Lidocaine belong to?
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CLASS I
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What r the properties of Prilocaine?
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-MEDIUM duration of action
-Pharmacological profile similar to Lidocaine -causes LITTLE VASODILATION. -can be used without a vasoconstrictor (similar to cocaine) |
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What r the properties of Bupivacaine?
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-LONG duration of action
-HIGHLY hydrophobic -HIGHLY potent -racemic mixture (R and S stereoisomers) |
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Which strereoisomer of Bupivacaine is less cardiotoxic?
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S isomer -Levobupivocaine
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What r the properties of Ropivacaine?
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-clinical effects similar to Bupivacaine but..LESS cardiotoxicity
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Local anesthetics are marketed as?
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Water soluble salts -usually the HYDROCHLORIDES
These salts are mildly ACIDIC |
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The acidic nature of the hydrochlorides salts convey what use to the local anesthetics?
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This property increases the stability of the anesthetic and any acompanying vasoconstrictor substance
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Why are local anesthetics less effective in infected tissues?
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Infected tissues have a low extracellular pH
-only a small fraction of the non-ionized local anesthetic is available to diffuse into the cell |
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Application of an anesthetic to a highly vascular area causes?
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-More RAPID absorption
-HIGHER blood levels This is different if used at poorly perfused areas e.g Tendons, Dermis, SC fat |
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What 2 drugs are used to augment local anesthetic effects in subarachnoid space and on peripheral nerves?
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CLONIDINE and DEXMEDETOMIDINE
This is because of their agonits action on alpha 2 receptors (like Epi) causing inhibition of Substance P release |
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What is the concern for patients with liver disease and the use of amide anesthetics?
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Amides are metabolized by the cyt P450 enzymes.
in liver disease metabolism is slowed -Toxicity is most likely to occur |
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Activated channels predominate at what membrane potential?
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POSITIVE membrane potential
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Channels in a rested state predominate at what membrane potential?
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A more NEGATIVE membrane potential
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What state of channels have a LOWER affinity for local anesthetics?
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Rested state
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The effect of a given drug concentration is more MARKED in which neurons?
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RAPIDLY firing neurons
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What type of fibres are blocked FIRST by local anesthetics?
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A delta fibres-small myelinated are blocked before larger myelinated (-A alpha, A beta and A gamma)
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What function is blocked LAST by local anesthetics?
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MOTOR function
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What neuromuscular effects does local anesthetics have?
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WEAK neuromuscular blocking effects
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At high concentation, Bupivacaine and Ropivacaine cAN cause?
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LETHAL arrythmias
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Which anesthetics are most commonly used for infiltration anesthesia? (to numb area of skin or a mucosal surface)
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Lidocaine
Procaine Bupivocaine |
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Why is BUPIVACAINE useful as an epidural anesthetic during labour?
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At low conc:
-it provides adequate pain relief WITHOUT significant motor block |
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What is Bier's block?
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Intravenous regional anesthetiA used occasionally for arm and hand surgery
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The End
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Hurray
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