Duan: Local anesthetics Flashcards by Megan Foggia

Do local anesthetics cause a loss of consciousness?

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What do local anesthetics do?

block axonal conduction in nerves when applied in appropriate concentrations

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Local anesthetics have a completely (blank) reaction

reversible

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What drug was discovered in 1860 by German chemist Albert Niemann?

cocaine

**made his tongue feel numb

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What did Sigmund Freud do with cocaine?

used it to treat morphine addiction

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What did Carl Koller (ophthalmologist) do with cocaine?

used it as the first local anesthetic on glaucoma patients

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What happened to Von Anrep, Freud, and Koller as a result of self-experimentation w cocaine?

they became addicted

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Cocaine is an (blank) that is a potent (blank) stimulant

ester; CNS

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Cocaine is a potent sympathomimetic and (blank)

vasoconstrictor

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What unfortunate events can cocaine cause?

fatalities from arrhythmias (v fib), MI, or seizures

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the first synthetic local anesthetic drug (1898), derivative of cocaine, slow onset , short duration, less potent, higher potential to cause allergic reactions, sympathomimetic (release adrenaline) increase heart rate, feel nervous

Procaine (Novocaine)

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slightly more potent with shorter duration of action than procaine

Chloroprocaine (Nesacaine)

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10 times more potent with slower onset and longer duration of action than procaine

Tetracaine (Pontocaine)

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does not contain the terminal hydrophilic amine group, only slightly soluble in water, slowly absorbed with prolonged duration

Benzocaine

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What is unique about Benzocaine?

it is only useful as a topical anesthetic

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List 4 ester local anesthetics and the duration of action/potency

cocaine - medium duration, potency =2
procaine - short duration, potency =1
tetracaine - long duration, potency =16
benzocaine **surface use only

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Lidocaine is an (blank) with execellent potency (2-3x more potent that procaine)

amide

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What should lidocaine be combined with to increase its duration of action?

epinephrine

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What is lidocaine used for?

surface anesthesia
peripheral nerve block
infiltration anesthesia
spinal anesthesia
epidural anesthesia 
antiarrhythmia

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This is an amide that is pharmacologically similar to lidocaine; it is coadministered w epi to prolong duration of action

Mepivacaine

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What is mepivacaine used for?

cardiovascular disease in elderly patients

What is unique about mepivacaine?

not useful in obstetrics bc of prolonged metabolism in fetus and neonate, which increases toxicity risk

This is an amide that is 10x more potent than procaine and has a particularly LONG duration of action (24hrs)

Bupivacaine

This is an amide with duration of action similar to bupivacaine, but slightly less potent

Ropivacaine

What is the mechanism of action of local anesthetics?

block voltage-gated Na+ channels in neuronal membranes that are responsible for signal propagation - the postsynaptic membrane will not depolarize and will thus fail to transmit an AP

How is specificity of anesthetics obtained?

by route of administration **highly effective analgesia (loss of pain sensation) in well-defined regions

Which nerves should be blocked first?

small-diameter, unmyelinated nerve fibers | large-diameter, myelinated fibers less susceptible and require greater doses to achieve neural blockade

What is more important to consider with nerves, size factor or myelination?

size factor

Rank the following in terms of predominant nerve blockage: small myelinated fibers small unmyelinated fibers large myelinated fibers

small unmyelinated > small myelinated > large myelinated

What is the order of sensory loss of the following? touch pressure pain temp

pain (lost first) > temp > touch > pressure (lost last)

What are 3 routes of administration for anesthetics?

regional: injected into area of nerve fibers to be blocked topical: surface use; esp on mucous membranes infiltration: inject under skin (often used with epinephrine to cause vasoconstriction)

When you get give anesthesia via an infiltration method (injected under skin), what should it be given with?

epinephrine **causes vascular constriction

Where is spinal vs epidural vs caudal anesthesia injected?

spinal: subarachnoid space epidural: outside of subarachnoid space, diffuses into subarachnoid space caudal: epidural space of the sacral canal

What procedures usually require a spinal anesthetic? Where is it injected?

upper-abdominal surgery; injected into subarachnoid space

What procedures usually require a caudal anesthetic? Where is it injected?

perinea and rectal procedures; injected into epidural space of sacral canal

What are epidurals usually used for? Where is it injected?

ob: labor and delivery, C-section; administered outside, but diffuses into subarachnoid space

What are three factors that affect the reaction of local anesthetics?

lipid solubility: the higher the lipid solubility, the faster nerve penetration, and onset of action pH influence: all local anesthetics are weak bases - decreased pH shifts equilibrium toward ionized form, which delays the penetration of the drug blood flow: vasoconstrictors (epi) are used to limit the vasodilation activity of local anesthetics

What is the pH equation we should be aware of?

log(ionized/uncharged form) = pKa - pH

What is the pH of all local anesthetics?

weak bases (pH 8-9)

What does a decrease in pH do to onset of action of local anesthetics?

shifts the equilibrium to ionized form, delaying penetration of the drug and onset of action

Why would you want to vasoconstrict when giving local anesthetics?

to keep the drug around longer and delay the systemic absorption of the drug into the bloodstream

Which anesthetics, esters or amides, are very rapidly hydrolyzed in blood

esters

Hydrolysis of esters yields (blank)

paraaminobenzoic acid (PABA)

almost completely biotransformed in liver by amidases and undergo N-dealkylation followed by hydrolysis by liver microsomal cytochrome P450

amides **pts with liver disease or taking other drugs affecting cyto P450 will reduce the biotransformation of amides

What do moderate doses of anesthesia do to the CNS? What do very high doses do to the CNS?

stimulate CNS; depress CNS

What affects do anesthetics have on the cardiovascular system?

depress myocardium reduce excitability lower contractility slow conduction

Which anesthetic causes vasoconstriction?

cocaine

Which anesthetics have the highest rate of hypersensitivity reactions?

esters, bc they form PABA which is known to be allergenic

What is the most common cause of toxicity w anesthetics?

high dose and systemic concentration due to unintentional intravenous injection

What are three toxic affects we should be aware of when administering anesthesia?

cardio toxicity allergic reaction neurotoxicity