Local Anesthesia Flashcards

1
Q

Using the Henderson-Hasselbalch equation, what are the two basic rules about the acid form versus the basic form of a drug?

A
  1. The acid form will have a proton that is lacking in the basic form.
  2. Either the basic form is negatively charged OR the acid form is positively charged.
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2
Q

Take a look at the 4th slide for how to figure out how much of the drug is in the basic form

A

Sure thing boss.

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3
Q

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?

A

10 times
100 times more
1000 times more acid

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4
Q

If your pka and your pH are the same, how much acid and base will you have?

A

Equal amounts

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5
Q

What does the aromatic group do to the local anesthetic?

A

It makes it lipophilic.

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6
Q

The local anesthetics favored in dental practice have what type of linkage between the aromatic part and the amine part?

A

Amides

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7
Q

The general structure of local anesthetics can be described as having three parts. What are they?

A
  1. Aromatic region (to make it lipophilic)
  2. Ester or amide linkage (this means it will be short lived in the blood due to enzymatic activity) (amide linkages are favored in dentistry)
  3. The amine group
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8
Q

T/F ester linkages are more allergenic than amides?

A

True

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9
Q

Amide (linkages) will have an I in their name somewhere prior to ‘caine’ such as Lidocaine.

A

Truth

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10
Q

Will ester linkages have an ‘I’ in their name somewhere prior to caine?

A

Nope. An example is procaine

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11
Q

T/F, The acidic and basic forms of the local anesthetic are important for the intended function? Why?

A

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.

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12
Q

T/F- in a chiral molecule, the S-, R-, and Racemic mixes of the drug have the same effect?

A

False- they can have similar or different pharmacokinetic and/or pharmacodynamic properties.

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13
Q

What is the basic mechanism of action for a local anesthetic?

A

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.

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14
Q

Is local anesthetic effective outside the axon?

A

Nope

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15
Q

Which form of the local anesthetic can pass through the membrane? Which form is better at blocking the channel?

A

Basic or uncharged form

Acidic or charged form

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16
Q

T/F, myelinated and unmyelinated axons are susceptible to local anesthetics?

A

True

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17
Q

We care about which types of nerve fibers? Why these ones?

A

A delta and C fibers.

Because they deal with pain and temperature.

18
Q

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?

A

Pain. This is good for us!

19
Q

Local anesthetics bind to the open form of the sodium channel. Will the nerve block occur faster on rapidly firing or slowly firing nerves?

A

Rapidly firing

20
Q

T/F, B and C fibers are more easily influence by drugs than A fibers? Why?

A

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.

21
Q

What must happen to achieve total nerve block? How is that achieved?

A

Activity at several nodes must be blocked

This is achieved by further diffusion of the anesthetic.

22
Q

T/F the faster a fiber is blocked, shorter it takes to recover?

A

False, the longer it takes to recover.

23
Q

T/F inflamed tissue is more difficult to anesthetize? Why?

A

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)

24
Q

Which type of drug has a longer duration- lipophilic or hydrophilic? Why?

A

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.

25
Q

The pKa can’t stray too far from physiological pH. Why?

A

Because if you do, then you’re only going to get one form of the drug. You need both the acidic (charged) and basic (uncharged) forms in order for the local anesthetic to work properly.

26
Q

Sometimes the pH is lowered from biological pH (6-7) to a pH of 4 or 5 to stabilize epinephrine. Why is it not a great idea to add a bunch of NaHCO3 to increase the concentration of free base?

A

Because you can precipitate out the local anesthetic

27
Q

T/F, local anesthetics can readily pass from the periphery to the CNS?

A

True

28
Q

Are CNS neurons sensitive to local anesthetics?

A

Yes, very.

29
Q

T/F concentrations of local in the blood stream that won’t affect the peripheral activity also won’t affect CNS activity?

A

False. Those concentrations will affect the CNS

30
Q

What happens if you inject some local directly into a vein?

A

You can block cardiac Na+ or Ca++ channels… clearly that is bad. This depresses pacemaker activity, excitability, and conduction, and contractility and this can produce hypotension. Yes, you could die!

31
Q

What does epinephrine do?

A

It’s a vasoconstrictor. So this makes the success rate and intensity better. The toxicity of the anesthetic is also reduced.

32
Q

T/F all local anesthetics will get absorbed into the blood stream? What should you do about that with lidocaine and procaine?

A

True

You should administer a vasoconstrictor with them because those drugs produce potent vasodilation

33
Q

Are unbound drugs free to diffuse to various tissues, like the CNS or placenta once they’re in the blood?

A

Indeed they are.

34
Q

How does the body keep the concentration of amide local anesthetics low?

A

The liver takes care of business

35
Q

What enzyme breaks down ester locals?

A

Pseudocholinesterase

36
Q

Just don’t do some inadvertent intravascular injections. How do you prevent this?

A

After inserting the needle you aspirated a little bit- this means you pull out on the plunger and see what you suck up into the tube. If there’s no blood, you’re good. If you suck up blood, then don’t inject your anesthetic there.

37
Q

The most serious side effects of local anesthetics are a result of what?

A

2 things- operator error:

  1. inadvertent intravascular injection
  2. excessive amounts of the drug
38
Q

What are some possible adverse side effects (the most serious ones) of local anesthetics?

A

the most serious are convulsions, respiratory arrest, and cardiovascular collapse

39
Q

What do you do if your patient is in respiratory distress?
Hypotension?
Cardiac function disruption?

A

Respiratory distress- ventilation, oxygen
Hypotension- epinephrine
Cardiac function disrupted- cardiopulmonary resuscitation

40
Q

What about using local anesthetic during pregnancy?

A

Lidocaine and prilocaine are category B drugs so they’re okay, but you might not want to use articaine because it’s category C