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Flashcards in Local Anesthetics Deck (43):

At what point in the pain pathway do local anesthetic work?

initiation, transmission, perception, or reaction?

transmission of the pain signal


What is a distinguishing characteristic of local anesthetics and how is their goal different from other pain management techniques?

the distinguishing characteristic is that they can provide complete loss of all sensory modalities

they're unique in that other forms of pain control want to try to be systemic, but local anesthetics try really hard to just be local


What are the three structural components of a local anesthetic:

the hydrophobic aromatic ring

the ester or amide linker

the hydrophillic amine


As the hydrophobicity of the aromatic ring increases, what happens to the LA's potentcy, duration of action, and toxicity?

potency goes up

duration of action begins sooner and lasts longer

toxicity also increases unfortunately


What are hte two types of linker bonds in LAs and how are the two classes different?

ester bonds or amide bonds

they are different in that they are metabolized differently

esters are more rapidly broken down in the plasma and also have a higher potential for allergic sensitization


What does the hydrophilic amine of an LA determine?

the pK of the drug - basically how much of the drug will be ionized at physiological pH


Are most local anesthetic weak acids or weak bases? What does this mean in terms of concentration of ionized drug?

weak bases with pK about 8-9


It means that at physiologic pH of 7.4, most of the drug will be ionized


Why are both the ionized and unionized form of the anesthetic necessary for the effect?

in order to enter the cell, the drug must be unionized

but in order to be effective and block the sodium channels, the drug must be ionized



So will a drug with a lower pK or higher pK have faster action?

lower pK

at lower pK you'll have less of the drug in the ionized form, so more will be able to cross the cell membrane into the neuron


Local anesthetics have higher affinity for the sodium channels when they are n what states? What does this means in terms of what neurons are most affected?

higher affinity for open and inactive states

less affinity for resting states

This means that neurons that are especially active will be affected first.


Why do local anesthetics block pretty much all transmission?

they block sodium channels, and literally all nerves use sodium channels

so it can block anything with a sufficient concentration of the drug


Do LAs preferentially block smaller diameter or larger diameter nerve fibers? Myelinated or unmyelinated?

will block small diameter nerve fibers faster

will block myelinated nerves faster than unmyelinated nerves of the same diameter


In what order are the modalities of sensation and motor function affected by LAs?

1. pain

2. cold

3. warmth

4. touch

5. deep pressure

6. motor function


What effect do LAs have on the cardiovascular system? Why is this a bad thing in terms?

they block Na+ channels in vascular smooth muscle, resulting in vasodilation

this is a bad thing because it counterintuitively promotes removal of the LA form the site of application, which decreases effectiveness and increases risk of toxicity


How do you pharmacologically circumvent the vasodilation effects of the LAs?

you give them with a vasoconstrictor like epinephrine to prolong action, decrease toxicity

also helpful because it decreases bleeding


What are some of the adverse CNS side effects of LAs?

tongue numbness (at even low concentrations)


visual disturbances


slurred speech

generalized convulsions

eventual coma


What cardiovascular adverse effects will the LAs have if they diffuse to the heart?

these are really bad - potentially fatal

hemodyanmic instability

decreased myocardial electrical excitability

decreased conduction rate/decreased force of ocntractions

cardiovascular collapse


In what type of LAs are hyeprsensitivity reactions more common? Why?

the esters

they are metabolized rapidly and one fo the metabolites - PABA - is easy to develop a hypersentivity to


What are the two reasons you don't want systemic distribution of a LA?

distribution decreases teh effectiveness because it dilutes the drug

distribution is associated with toxicity because ou don't want Na+ channels blocked in the CNS or CV systems


What is the negative impact of using a vasoconstrictor like epinephrine with LA when closing significant wounds?

they can have a negative impact by reducing blood flow, which makes healing ultimately harder


Why might LAs be less effective when injected to inflammed/pruritic areas?

inflammaton and pus formation makes the area more acidic, with a pH about 5.5-6.5

this means that the vast majority of the drug will be ionized right away and less likely to enter the neuron, reducing the anesthetic effect


Which form: esters or amides distribute more widely?

the amides, since they take longer to metabolize


What enzyme hydrolyzes the esters and where?

the pseudocholinesterases in the plasma


How and where are the amides metabolized?

they are hydrolyzed in the liver by mixed-function oxidases


How are LA metabolites excreted?



What is EMLA?

It's a eutetic mixture of local anesthetics

lidocaine and prilocaine

it's an oil at room temp, so you put it on intact skin to numb the area over where you're going to do an LP, venipuncture, or skin graft harvesting


What is the most common route of administration for the LAs? What do you need to be careful for with this route?

infiltration anesthesia - injected subcutaneous or submucosal for minor surgery or dental procedures

you need to be careful that you don't inadvertently inject it into the vascular system - you dont want systemic action


How would you administer an LA if you wanted to block nerve conduction in a bigger area like the finger or the arm?

a nerve block

injection into thte brachial plexus will anesthetize the whole extremity


What's another name for an intravenous regional block and when can you use it/what's the danger?

 A bier block

You can only use it on the extremities because you need to block the diffusion fo the drug by placing a touniquet and leaving it on for at least 15 minutes


How does an epidural work and what nerves does it primarily work on?

you inject LA into the epidural space of the spinal cord - primarily works on spinal nerve roots


Why is there a concern for systemic distribution with epidural injections?

they can diffuse into the blood stream following absorption from the epidural space

so give with epinephrine and use a dilute solution fo bupivacaine during labor to avoid respiratory depression in the neonate


Why are spinal local anesthetics helpful sometimes?

they are best at anesthetizing very large regions - you inject it into the CSF of the lumbar space

nice because it doesn't really get into the blood at all with this route


Is procaine an ester or amide? What does that mean for it's duration of action and metabolism?

it's short acting because it's rapidly metabolised in the plasma - thus not useful as a topical anesthetic


What is the most widely used local anesthetics?



Is lidocaine an ester or amide?

amide - metabolized in the liver


What is lidocaine used for besides as a LA?

an antiarrhythmic agent


lidocaine OD can produce death due to....

ventricular fibrillation or cardiac arrest


What local aneshetic works very similar to lidocaine, but with a longer duration of action?



What is the major pro to bupivacaine?

it's very potent and long-acting, making it perfect for epidural blocks and prolonged surgery


What is the benefit to ropivacaine over bupivacaine?

it has fewer CVS and CNS toxicities


What LA is common used for topical anesthesia of the eye, nose, and throat?



What is the added benefit that is unusual to cocaine?

It actually has vasoconstrictor action instead of vasodilation - so it's great at numbing areas and stopping bleeding

(especially in the mucosal membranes - so cut lips)