Exam 4 LA's part 1 Flashcards
What class are LA’s?
Class 1 sodium channel blockers
What is the lipophilic part & what is the hydrophilic part of LA’s?
Aromatic group & amino group
How are amides & esters differentiated & what is the exception?
- Amides have 2 I’s & esters have 1.
- Except cocaine it’s an Amide
What kind of intermediate chain do esters have?
What about amides?
- Esters have a hydrocarbon chain.
- Amides have a amine group
What ester has the highest potency & why?
Tetracaine, it’s very lipid soluble
What ester has the longest duration of action?
Tetracaine 60-180mins
What amide has the fastest onset?
Lidocaine
What promotes a longer duration of action for LA’s?
It’s protein binding capability (that is for intravascular, not local)
The closet the pK is to the pH the ____ LA’s act?
Faster
Lidocaine needs to be in what form to enter the cell?
Non-ionized & lipid soluble
Besides Na+ channels, what are the other sites of action for LA’s?
K+ channels, Ca2+ ion channels, GPCR’s
LA’s do not work in what kind of environment & why?
In acidic environment. It becomes ionized
How many nodes of Ranvier need to be blocked to localize an area?
2-3 Nodes (~1cm)
What would be affected if a LA epidural was injected into a vein instead of epidural space?
Preganglionic B fibers of the SNS
The rate of clearance of LA’s is dependent on what?
Cardiac output & protein binding
Which LA has the fastest metabolism?
Procaine. It has the least protein binding
What amide has the fastest metabolism?
Prilocaine
How are esters metabolized?
- Via hydrolysis by plasma cholinesterases.
- Except cocaine, which is via liver
Which LA’s can cause allergies & what causes the allergy?
Esters d/t metabolite Para-aminobenzoic acid (PABA)
What LA’s have a pulmonary first-pass extraction?
- (B)upivacaine
- (L)idocaine
- (P)rilocaine
Which local anesthetic property is most important when it comes to the duration of action?
Lipid solubility > clearance > protein binding
Which type of LA is preferred in pregnancy?
Ester. D/t amides protein binding & crossing placenta causesing Ion trapping in fetus
What LA has the most protein binding?
Bupivacaine
What is the infiltration dose for lidocaine?
300 mg plain & 500 mg w/ Epi
What LA’s can cause Methemoglobinemia?
Prilocaine & benzocaine
What is the dose of methylene blue?
- 1-2 mg/kg IV over 5mins
- Do not exceed 8 mg/kg
What protein does bupivacaine bind to?
Alpha-1 glycoprotein
Esters get hydrolized, list the 3 esters from fastest to slowest hydrolysis?
Chloroprocaine > procaine > tetracaine
Which LA is not a weak base?
Benzocaine
What is the onset & duration of benzocaine?
- Rapid onset.
- Duration 30-60mins
A 65 yo Pt with methemoglobinemia, weighing 120lbs, need methylene blue, what is the max dose?
54.55kg x 8 mg/kg= 436.4 mg
