Local Anesthetics Flashcards
What letter do all amides have?
Two I’s
What determines the lipid solubility of the drug?
The aromatic ring and hydrocarbon chain length
Do high or low lipid soluble drugs penetrate cells quicker?
High lipid solubility
Are amides or esters more stable overall?
Amides
What does the metabolism of esters result in? Amides?
Production of PABA for esters
Nothing really for amides, which is why they are more commonly used now
Are all locals weak or strong bases?
Weak base-so they exist as ionized and unionized
As pH increases (More basic), there is ____ ionized particles of LA
Less, meaning more LA will enter the cell
As pH decreases (more acidic) there is ____ ionized particles of LA in the cell
more
So if a patient is acidotic for some reason, how will that affect LAs?
They won’t be as effective
What is LAs MOA?
Reversibly bind to voltage gated Na channels. This blocks Na influx and AP and nerve conduction
What size of fibers are LAs more effective at blocking?
Small
Do myelinated or non myelinated fibers get blocked first?
myelinated
The loss of nerve function proceeds as ……
Put these in order: Loss of pain, temp, skeletal muscle, touch, and proprioception
Pain, temp, touch, proprioception, skeletal muscle tone
What type of fiber transmits pain and temp?
A delta, which is myelinated
What type of fiber transmits pain and postganglionic signals?
C, nonmyelinated
Explain in depth of LA block Na channels.
The LA exists in equilibrium as ionized and unionized outside the cell membrane. The unionized part can diffuse into the cell, then get ionized with H+ (or maybe others as well). It then binds to the receptor, blocking it.
What is each Na channel comprised of?
A single alpha subunit containing a central ion conducting pores associated with accessory beta subunits
What are the factors that control absorption and distribution of LAs?
Vascularity, protein binding (slowly metabolized)
What is the biggest factor for duration of action?
Protein binding
Procaine is 6% protein bound and has a short duration of action wheras bupivacaine is 95% bound and has a long duration of action
How much can LA duration of action be increased with coadministration of epi?
2X using 1:200,000 epi
What is the metabolism of esters? Besides cocaine
Plasma cholinesterase
How is cocaine metabolised?
Hydrolyzed in the liver
How are amides metabolized?
Amidases
What are the ADEs of LAs?
CNS-Excitation followed by depression and death due to respiratory depression
CV- Bradycardia, heart block, vasoldilation (hypotension)
Allergic reactions-More common with esters r/t PABA
What are the contraindications to LAs?
Heart block, concurrent use if quinidine, flecainide, disopyramide, and procainamide, and prior use of amiodarone
What are the three causes of possible LA toxicity
IV injection
Rapid absorption from vascular area
Overdose
What are the factors that reduce toxicity?
Use smallest dose possible
Lower dosage on frail patients
Inject slowly and aspirate to ensure not in vessel
Add epi
What is the max dose of epi to give with LA?
200mcg
What area should we avoid using epi with the LA?
In areas with end arteries d/t possible development of necrosis due to prolonged hypoperfusion
What is a unique characteristic of cocaine?
It produces localized vasoconstriction as well as anesthesia
What two drugs are not good substitutes for cocaine?
Procaine and chloroprocaine
Which LA has the potential to cause methemoglobinemia?
Benzocaine
How long can bupivacaine blocks last?
Up to 24 hours
What is the issue with prilocaine?
Can also cause methemoglobinemia
What is unique about articaine?
It is technically an amide, but it contains an additional ester group that helps it to be metabolized quicker
What is the most commonly used dental anesthetic?
Articaine
What is the name for combination of LAs?
EMLA
