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Flashcards in Local Anesthetics - Slattery Deck (15):
1

What types of drugs change the way that pain is percieved?

General Anesthetics and opioids

2

There are three structural compenents of drugs:
Hydrophobic, linker, and hydrophilic components

What does hydrophobicity do for the drug?

Increase the potency
Increase plasma protein binding
Increase action duration
Increase toxicity

3

There are three structural compenents of drugs:
Hydrophobic, linker, and hydrophilic components

What does the linker do for the drug?

Determines the mentabolic fate of the drug

Esters vs Amides
Esters are rapidly broken down in plasma and a high potential for allergic sensitization

4

There are three structural compenents of drugs:
Hydrophobic, linker, and hydrophilic components

What does the hydrophilic component do for the drug?

It determines the pK of the drug

5


How does the pK affect local anesthetic drug effectiveness?



Local anesthetics are weak bases (pK about 8-9) and the proportion of ionized vs ionized drug is determined by the pH of the environment and pK of the hydrophilic region of the drug Ionized form of drug not lipid soluble, can’t cross plasma membrane Ionized and un-ionized forms in equilibrium Un-ionized form of drug can cross membrane


6

So what is different in rate of onset of action between the lower pK vs higher pK drugs?

Lower pK drugs have more rapid onset of action
-more uncharged form at physiological pH
-rapid diffusion into cytoplasm
-once inside cytoplasm they ionize and activate

7

What is the anesthetic's affinity like for the different states of the Na channel?

Low affinity for resting state
High affinity for open or inactive states

Block Na channels from the inside

8


What is the difference in susceptibility of different nerve fibers to block by anesthetic?



Preferentially block smaller diameter nerve fibers -Some debate here



Myelinated nerves are blocked before unmyelinated nerves of the same diameter



 



(No cade, I don't completely understand why exactly this is. Slattery said it, but I still don't have a good explanation as to why)



(Maybe size plays a bigger role than myelination, so thats why it is in that basic order)


9

Why would you want to include epinephrine along with your local anesthetic?

LA's can block sodium channels in vascular smooth muscle to promote its removal from a localized site
-this will increase the risk of toxicity and lower the drug's effectiveness

epinephrine is a vasoconstrictor that will prolong the action, decrease toxicity, and decrease bleeding

10

Why can local anesthetic be bad if it hits your heart?

Decreased myocardial electrical excitability
-Decreased conduction rate
-Decreased force of contractions

Cardiovascular collapse
-Potentially fatal

11

Why do you tend to see hypersensitvity reactions with ester-type and not amides?

Esthers are more rapidly broken down in the plasma

12

If there is a lot of pus or inflammation at the site where you are injecting the LA what might be a complication you should think about?

Extracellular pH is lower in infected tissue
-This means that more of the drug will be ionized and unable to cross into the cytosol
-This means that there will be less anesthetic effect on the neurons

13

What is the advantage of mixing a couple LA's in an EMLA (Eutitic Mixture of Local Anesthetics)

Mixture has a melting point less than either compound alone
Exists as an oil at room temperature, can penetrate intact skin
Effective for procedures such as lumbar puncture, venipuncture, skin graft harvesting, etc.

14

After doing a nerve block the patient gets scared and tries to take off the tourniquet. Why would this be bad???

If you take it off too fast, then the drugs would be distributed systematically and cause heart problems

15


Which local anesthetics are ester and which are amide type local anesthetics? cocaine, lidocaine, tetracaine, procaine, ropivacaine, prilocaine, dibucaine.



Amide-type: mepivicaine Bupivicaine Ropovicaine Lidocaine Ester: Cocaine Tetracaine Procaine



"I before caine = amide" (usually)