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33 Cards in this Set
- Front
- Back
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What channels do local anesthetics target? When do they bind? What do they effectively do?
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• Voltage-gated Na+ channels
• High affinity binding during the activated stage (channel opening) • Acitvated (open) > Inactivated > Resting (closed) channels • Effectively lengthen the refractory period |
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Which group of local anesthetics: esters or amides have a shorter half-life? Why?
What common group is ionizable and thus affected by pH? |
• Esters have a shorter half life.
--They are hydrolyzed faster by cholinesterase in the blood -- Amides are hydrolized by cyt. P450 in the liver. • Tertiary amine (connected to the aromatic ring by an ester or amide bond) is ionizable |
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What determines onset & offset of effect?
What may be added to reduce systemic absorption? What receptors are targeted? |
• Diffusion.
• Epinephrine (vasoconstrictors) • α2 receptors |
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What is of concern if injecting a local anesthetic such as cocaine, procaine, tetracaine, or bezocaine into the CSF?
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• They are all esters
• There is no cholinesteraste in the CSF • Possible in ↑ duration of action! |
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Why might some poepl have an allergic rxn to all of the following: cocaine, procaine, tetracaine, or bezocaine?
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• They are all esters
• They are hydrolized by cholinesterase to p-aminobenzoic acid --> allergic rxn in some. |
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How are amides hydrolyzed in the body?
What concerns might this lead to? How are amides transported in the body? What causes the effect? |
• Amides are hydrolized by CYP34A
• May have ↑ toxicity in liver disease & CYP34A metabolizes many drugs (alfentail, midazolam) • Transported by being bound to proteins (α1-glycoprotein) but it is the [Free drug] that determines effect and toxicity • α1-glycoprotein is ↓ in neonates & BC users and ↑ in smokers, cancer surgery, MI, uremia |
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What types of nerves are preferentially targeted?
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• Myelinated >> unmyelinated (fewer Na+ channels to activate - only those at nodes of ranvier)
• Small diameter >> large diameter • Location in large nerve bundle (motor on the outside, proximal sensory outer portion & distal sensory in core) |
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What type of nerve fibers are responsible for conducting pain? Why are they preferentially affected?
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• C-fibers (C-dorsal root & C-sympathetic)
• Preferentially targeted because 1. Small diameter 2. High Firing frequency. C-dorsal root fiberes are unmyelinated, but C-sympathetic fibers are myelinated |
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What CNS effects/toxicities can result from local anesthetics?
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• @ [low]: Sleepiness, lightheadedness, tongue numbness, metallic taste
• [high]: Nystagmus, shivering, *tonic-clonic convulsions/seizures*, CNS depression --> death |
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In the case that a high dose of local anesthetic was given and a seizure resulted what drugs would be given and what other interventions would be made to rescue the patient?
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• Diazepam (IV, benzo)
• Thiopental (short-acting barbiturate) • Succinycholine (IV, neuromuscular blocking, short-acting) • Hyperventilation (↑ blood pH) |
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What cardiovascular effects/toxicities can result from local anesthetic use?
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• Blocking of Na+ channels in the <3 leads to ↓ of abnormal pacemaker activity
• (-) ionotropic effect & arterial dilation --> hypotension & myocardial depression • Cardiovascular collapse & eath are rare |
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In addition to its effects on Na+ channels, what else does cocaine impact?
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• Blocks NE uptake, can cause cardiac arrythmias
• Vasoconstriction (ulceration in chronic abusers) • Hypertension |
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What local anesthetic is the most cardiotoxic? What rescue Tx is prescribed in the case of toxicity?
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• Bupivacaine --> causes electromechanical dissociation which can be fatal
• Tx: Epinephrine, atropine, and bretylium |
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What local anesthetic is associated with oxidation of hemoglobin to methemoglobin? What is the mechanism? What is the Tx?
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• Large doses of prilocaine --> o-toluidine which oxidizes hemoglobin to methemoglobin
• Tx: IV methylene blue or vitamin C |
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What is nerve block anesthesia? What drugs are used?
What types of drugs work faster? What determines the drug dose? |
• Nerve block = complete, temporary, local anesthesia
• Lidocaine & bupicacaine are used • Drugs w/ low pKA work faster (more often in the hydrophobic sate) • Dose depends on location and the amount of vascularziation there |
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What is complex regional pain syndrome?
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• Pain, swelling, ↓ ROM, vasomotor instability, cyanosis, mottling, ↑ sweating. Occurs after injury, surgery, or vascular event (MI, stroke)
• Stage 1: pain, local edema • Stage 2: edema, muscle wasting, skin ∆s • Stage 3: ↓ ROM |
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What local anesthetics are amides? Why is it important to make this distinction?
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• Lidocaine, Mepivacaine, Bupivacaine, Prilocaine, Ropivacaine (all have two i's)
• Important b/c amides are longer acting than esters which are rapidly hydrolyzed by cholinesterase |
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What local anesthetics are esters? Why is it important to make this distinction?
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• Cocaine, procaine, tetracaine, benzocaine (do not have two i's)
• Important to distinguish from amides b/c esters are shorter-acting than amides b/c they are rapidly hydrolyzed by cholinesterase |
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Long duration local anesthetic. Ester class.
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Tetracaine
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Medium duration local anesthetic. Ester class.
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Cocaine
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Short duration local anesthetic. Ester class.
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Procaine
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Topical only - local anesthetic. Ester class.
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Benzocane
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When using local anesthetics that are esters, systemic absorption is proportional to ______?
• Weak bases or acids? • Which form is able to pass through the cell mb? • Which form binds to the channel? • What does this mean? |
• Systemic absorption is propotional to vascularization
• Esters are weak bases. • Lipophilic form binds to the channel (not hydrolized) • Hydrophilic/Hydrolyzed form binds to the channel • Means that the drugs are pH depenent and ionization is important. |
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What enzyme hydrolyzes local anesthetics of the ester class?
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• Butyrlcholinesterase.
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What is the MOA of local anesthetics?
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• State dependent blockage of voltage dependent Na+ channels
• Prevents depolarization & conduction of AP in excitable cells, especially neurons (when given near neurons) |
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What are the CNS side affects associated with local anesthetics?
• What are the respiraotry side effects? • What are the CV effects? What is a risk at [high]? • What other side effects are of concern? |
• CNS: light headiness or sedation, restlessness, nystagmus, tonic-clonic convulsions (treat with sedative hypnotics). • Respiratory and cardiovascular collapse. • CV: except cocaine all are vasodilators, heart block, Arrhythmias, hypotension. • High concentrations may permanently damage nerves. • ***Esters can form metabolites that create hypersensitivity reactions*** |
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What adverse effect can be perpetuated by the metabolites from ester local anesthetics?
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Ester metabolites can create hypersensitivity rxns.
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Which local anesthetic is the most cardiotoxic?
What specifically are the cardiac concerns? What class of anesthetics is this drug a part of? |
• Bupivicaine
• Causes arrythmias & hypotension (potentially irreversible) • Amides |
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What local anesthetic can be metabolized th methemoglobinemia?
How is this treated? What class of anesthetics is this drug a part of? |
• Prilocaine
• Treat w/ methylene blue • Amides |
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What local anesthetic can also block norepinephrine reuptake leading to vascoconstricting action and cardiovascular toxicity?
What specifically are the CV risks? What class of anesthetics is this drug a part of? |
• Cocaine
• CV risks = hypertension, cerebral hemorrhage, arrythmias and MI's • Esters |
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Long duration local anesthetic. Amide class. (3)
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• Bupivacaine
• Ropivacaine • Etidocaine mne: All amides have two i's. Long acting - BERrrrrrrrrr! |
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Medium duration local anesthetic. Amide class. (3)
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• Lidocaine
• Prilocaine • Mepivacaine mne: All amides have two i's. Medium acting - L, M, n, o, P |
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Which nerve fibers are most sensitive to local anesthetics? Which are least sensitive?
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Most sensitive: rapid firing, small diameter "C" fibers & medium diameter, myelinated B sympathetic pregagnlionic fibers
Least sensitive: Large diameter, slow firing, myelinated "A" type motor neuron fibers |
