Local Anesthesia Flashcards
(40 cards)
Using the Henderson-Hasselbalch equation, what are the two basic rules about the acid form versus the basic form of a drug?
- The acid form will have a proton that is lacking in the basic form.
- Either the basic form is negatively charged OR the acid form is positively charged.
Take a look at the 4th slide for how to figure out how much of the drug is in the basic form
Sure thing boss.
If your pH is 1 unit higher than your pka (for example, say your pka is 4 and your pH is 5) then how much more acid than base will you have? What about for 2 units? 3 units?
10 times
100 times more
1000 times more acid
If your pka and your pH are the same, how much acid and base will you have?
Equal amounts
What does the aromatic group do to the local anesthetic?
It makes it lipophilic.
The local anesthetics favored in dental practice have what type of linkage between the aromatic part and the amine part?
Amides
The general structure of local anesthetics can be described as having three parts. What are they?
- Aromatic region (to make it lipophilic)
- Ester or amide linkage (this means it will be short lived in the blood due to enzymatic activity) (amide linkages are favored in dentistry)
- The amine group
T/F ester linkages are more allergenic than amides?
True
Amide (linkages) will have an I in their name somewhere prior to ‘caine’ such as Lidocaine.
Truth
Will ester linkages have an ‘I’ in their name somewhere prior to caine?
Nope. An example is procaine
T/F, The acidic and basic forms of the local anesthetic are important for the intended function? Why?
True.
The uncharged basic form allows for the local to get inside the nerve. Once inside, the charged version has a better ability to bind to the Na+ channel and inhibit the conduction of a nerve impulse.
T/F- in a chiral molecule, the S-, R-, and Racemic mixes of the drug have the same effect?
False- they can have similar or different pharmacokinetic and/or pharmacodynamic properties.
What is the basic mechanism of action for a local anesthetic?
Local anesthetics cross the axon membrane and interact with the open and inactivated forms of the Na+ channel, blocking sodium conduction. No more sodium ions can come in and the drug remains in the inactive sodium channel.
Is local anesthetic effective outside the axon?
Nope
Which form of the local anesthetic can pass through the membrane? Which form is better at blocking the channel?
Basic or uncharged form
Acidic or charged form
T/F, myelinated and unmyelinated axons are susceptible to local anesthetics?
True
We care about which types of nerve fibers? Why these ones?
A delta and C fibers.
Because they deal with pain and temperature.
When a local anesthetic is acting on C fibers (pain) compared to acting on A beta fibers (touch and pressure), which fiber returns to normal function slowest?
Pain. This is good for us!
Local anesthetics bind to the open form of the sodium channel. Will the nerve block occur faster on rapidly firing or slowly firing nerves?
Rapidly firing
T/F, B and C fibers are more easily influence by drugs than A fibers? Why?
True.
Because A fibers are really big compared to B and C fibers. The drug has to diffuse over a longer distance on A fibers.
What must happen to achieve total nerve block? How is that achieved?
Activity at several nodes must be blocked
This is achieved by further diffusion of the anesthetic.
T/F the faster a fiber is blocked, shorter it takes to recover?
False, the longer it takes to recover.
T/F inflamed tissue is more difficult to anesthetize? Why?
True.
This is because the cells release things in inflammation that lower the pH, making it more difficult to get the drug inside the axon (remember that the uncharged or basic version of the drug is best at getting inside the axon)
Which type of drug has a longer duration- lipophilic or hydrophilic? Why?
Lipophilic because it is going to be bound to a protein and protected from clearance in the blood. Hydrophilic drugs will go in the blood very well and be more susceptible to enzymatic clearance.
