Pharmacology-Local Anesthetics

Front 1

Which drugs are used more often in the dental office than any other?

Back 1

Local Anesthetics

Front 2

What are the major properties of the ideal local anesthetic? (11 items)

Back 2

1) Potent local anesthetic
2) Needs to be reversible
3) Absence of local reactions
4) Absence of allergic reactions
5) Rapid Onset
6) Satisfactory Duration
7) Adequate tissue penetration
8) Low Cost
9) Stability in solution (won't degrade)
10) Sterilization by autoclave
11) Ease of metabolism & excretion

Front 3

What 2 major groups are local anesthetics divided into chemically?

Back 3

Amides & Esters
(The division is associated with potential allergic reactions.)

Front 4

Why are esters not used as much as they once were?

Back 4

Due to the allergic reactions they produce.

Amides don't produce allergies.

Front 5

Where are esters largley metabolized? Amides?

Back 5

In the plasma, amides are metabolized in the liver

Front 6

The aromatic nucleus {R} is ___________ and the amino group is _________

Back 6

lipophilic (lipid soluble)
hydrophilic (water soluble)

*Lipophilic compounds pass through the
lipid bi-layer-->faster onset. The hydrophilic compound hangs out in the "water".*

Front 7

What does a nerve action potential result in?

Back 7

The opening of sodium channels & and inward flux of sodium.
**If a local anesthetic can stop the propigation of electricity-->the opening and closing of sodium channels then the nerve doesn't "feel" anything.**

Front 8

The outward flow of ________ _______ repolarizeds the membrance and closes the sodium channels.

Back 8

potassium ions

Front 9

With regard to the action potential, what chemical opens channels and what chemical closes them?

Back 9

Sodium ions opens them
Potassium ions close them.

Front 10

What is the range for the charge to open/close the sodium ion channels?

Back 10

The membrane potential begins at -90 to -60mV and closes when it reaches +40mV

Front 11

Where do local anesthetics attach them selves?

Back 11

To specific receptors in the nerve membrane.

**After combining with the receptor LA's ( local anesthetics) block conduction of nerve impulses by decreasing the permeability of the nerve cell membrane to sodium ions. (It doesn't allow the influx of sodium).**

Front 12

If a LA (local anesthetic) passes easily through the lipid bi-layer what is the rate of onset?
How about its rate of "off-set"?

Back 12

It will have a fast onset and "off-set".

The trick is to not have it "off-set" too soon.

Front 13

Decreasing the permeability to sodium ions does what to the action potential?

Back 13

It decreases the rate of depolarization of the nerve membrane. (Stops the propagation of the action potential)
**This means you've raised the threshold and greater stimulus is needed for the action potentail to happen.**

Front 14

LA's reduce permeability by competing with ________ for the membrane binding sites, and thus prevent the onset of nerve conduction.

Back 14

Calcium

Front 15

When a LA is injected into tissues, the rate of absorption depends on the __________ of those tissues.

Back 15

vascularity

Front 16

The greater the blood flow in an area the greater the chance of ________ ______.

Back 16

systemic toxicity

(you don't want the LA to be absorbed by the blood because it needs to get to the nerve and block the action potentials.)

Front 17

What is added to the local anesthetic to reduce its absoroption by the blood stream?

Back 17

A vasoconstrictor.

This also reduces systemic toxicity by keeping the LA where you want it!

Front 18

When the LA is in a cartridge, the pH is 4.5, once its injected into tissues the pH of the body is at 7.4 so the amount of local anesthetic in the free-base form increases. What does this mean with regard to the tissues?

Back 18

There is greater tissue (lipid) penetration.
Might want to re-read pg 114 in the book.

In an acidic environment the amount of free base is reduced-->so it can't cross the lipid bi-layer as easily.

Front 19

If a free-base form of the LA is needed to penetrate the nerve membrane, what does this mean from a pH standpoint?

Back 19

You want a more "basic" environment…something with a higher pH like the 7.4 range of the body to enable the product to cross the lipid bi-layer.

Front 20

If infection is present, what does this mean about the localized pH level?

Back 20

Its usually reduced and is forming an acidic environment.

Front 21

Knowing that the sight of infections is more acidic than the rest of the body, what does this mean about where you'd place the LA?

Back 21

It means you might need to place it at a slightly different location so it could cross the lipid bi-layer and stop the action potential.

Front 22

If the LA is ___________ it will pass through the lipid bi-layer.
If its _________ it won't pass through and is blocked.

Back 22

Ionic (needs a hydrogen ion core)

Cationic

Front 23

Concerning absorption of the LA…with reduced absorption by the blood stream the chance of _______ toxicity is reduced.

Back 23

systemic (need to decrease vascularity)

Front 24

What is often added fo LA to reduce absorption into the blood stream?

Back 24

Epi

Front 25

What are the 3 big reasons to have a vasoconstrictor?

Back 25

1) Reduces the blood supply to the area
2) Limits systemic absorption
3) Reduces systemic toxicity

Front 26

What can be said about the absorption of LA using topical application?

Back 26

There is good absorption, especially on mucous membranes. Skin doesn't have quite as good of an absorption rate however.
** On mucous membranes absorption can approximate that produced by Intravenous injection.**

Front 27

Highly vascular organs are likely to have (higher/lower) concentrations of anesthetics?

Back 27

Higher…but if no nerve is present there then there is no action.

Front 28

Can local anesthetics cross the placenta? What about the blood/brain barrier?

Back 28

Yes to both.

May want to hold off Tx if Pt is pregnant.

Front 29

LA's are metabolized differently.
Esters are metabolized by _________ pseudocholinestrases & liver estrases

Back 29

Plasma

Front 30

Amide LA's are metabolized primarily by the __________

Back 30

Liver

Front 31

What is methemoglobinemia?

Back 31

When RBC's won't pick up oxygen molecules.

Can occur with large doses of prilocaine.

Front 32

Metabolites & some unchanged drug of both esters & amides are excreted by the ___________

Back 32

Kidneys

*Need to be especially aware with PT's who have kidney disease as this can be a problem.*

Front 33

What is the common order of nerve function loss when LA's are involved? (9 items)

Back 33

1) Autonomic
2) Cold
3) Warmth
4) Pain
5) Touch
6) Pressure
7 Vibration
8)Propriception
9) Motor

*If pain is gone but pt still feels light pressure-->that's normal.

Front 34

Adverse reactions and toxicity are directly related to the _________ level of the drug.

Back 34

Plasma

Front 35

What are some factors influencing toxicity?

Back 35

The drug itself Concentration,
Route of administration,
Rate of injection,
Vascularity,
Pt's weight & Rate of metabolism/excretion.

Front 36

What two main systmes are affected by LA's toxicity?

Back 36

Cardiovascular & CNS

*Could result in a seizure in the CNS or stimulation may occur before CNS depression.**

Front 37

Elective dental Tx should be rendered before a Pt becomes pregnant.
What drug can be used however in pregnant pt?

Back 37

lidocaine

**Fetal bradycardia has been reported however when using larger doses on a near term mother.**

Front 38

Do amides or esters usually produce allergies?

Back 38

esters
**If Pt indicates allergies to LA's more history should be elicited from PT before a local anesthetic is chosen. True allergies to amides have not been documented.**

Front 39

If a Pt experiences hives, rash or itching with use of LA, what is usually in response to?

Back 39

The preservatives of the amides.
(Sulfite, LA's with vasoconstrictors also contain sulfites.)

Front 40

What is the only class of LA to be used parenterally?

Back 40

Amides.

(Esters are occasionally used topically)

Front 41

Which amides is considered the BEST!

Back 41

lidocaine

Front 42

Why is lidocaine considered the best?

Back 42

It has a rapid onset related to its tendency to spread well through out the tissues.

Front 43

In dentistry, lidocaine__% with a (what ratio) epinephrine is used for infiltration and block anesthesia.

Back 43

2% with 1:100,000

Front 44

When using lidocaine w/epi 1:100,000, what is the usual duration of pulpal anesthesia?

Back 44

1-1.5 hours
(Soft tissue anesthesia is maintained for 3-4 hours)

Front 45

If lidocaine is used for topical anesthesia, what % is it as an ointment?

Back 45

5%

Front 46

What is the usual dose for mepivacaine, which is commonly used in dentistry as well?

Back 46

2% solution w/the additional of 1:20,000 levonordephrin (levo) as a vasoconstrictor.

Front 47

Since mepivacaine produces _____ vasodilation than lidocaine, it can be used as a ___% solution without a vasoconstrictor.

Back 47

less
3%
(It can be used for short procedures when a vasoconstrictor is contraindicated--not often.

Front 48

How often is prilocaine used in dentistry? Why?

Back 48

Not a whole lot..due to methemoglobinemia

*Prilocaine should not be administered to Pt's with any condition in which problems of oxygenation may be especially critical.*

Front 49

Where is prilocaines niche in dentistry?

Back 49

In procedures where the desired duration of action is someone longer than that obtained with mepivacaine both with & without vasoconstrictor

Front 50

What is another potential advantage of prilocaine?

Back 50

The concentration of epinephrine (1:200,000) is lower than in other local anesthetic amide combinations.

Front 51

What can be said about bupivacaine compared to other amides?

Back 51

It is more potent but less toxic than other amides.

Front 52

What can be said about the duration of bupivacaine compared to other amides?

Back 52

bupivacaine has the longest duration.

*It's extremly good for post- opp pain. Indicated for lengthy dental procedures when pulpal anesthesia is needed for more than 1.5 hours.**

Front 53

In a 0.5% solution of bupivacaine what is the concentration of epi?

Back 53

1:200,000

Front 54

When should bupivacaine not be used in patients?

Back 54

If prone to self-mutilation (lip biting) or in Pt's with cardiac conditions.
*Can be very cardio toxic*

Front 55

articaine allows for greater _______ solubility & the ability to cross _______ barriers such as nerve membranes.

Back 55

lipid

lipid barriers

Front 56

What is it about articaine that allows for this greater lipid solubility?

Back 56

Its derived from thiophene.

Front 57

What is it about the chemical structure of articaine that separates it from other local anesthetics?

Back 57

It has an extra ester linkage.

**This mean it can be degraded more quickly in the blood.**

Front 58

What % of articaine is metabolized by the liver vs the amount metabolized by the blood?

Back 58

5-10% is metabolized by the liver 90-95% is metabolized in the blood.
**Remember the extra ester linkage allows for the blood degradation.**

Front 59

What is one of the best properties of articaine?

Back 59

Its ability to supplement lidocaine in the MN.

Front 60

What % solution is articaine?

Back 60

4% solution

*FYI, it rarely causes paresthesia after a MN block.**

Front 61

Where is articaine secreted?

Back 61

In the Kidneys!

Front 62

Since articane is a 4% concentration what is the epi content?

Back 62

1:100,000

Front 63

How are esters most commonly used?

Back 63

Topically!

*No esters are currently available in a dental cartridge.**

Front 64

What are 5 reasons for the use of a vasoconstrictor to be used in a local anesthetic?

Back 64

1) Prolong the duration of action
2) increase the depth of anesthesia
3) delay systemic absorption
4) reduce the toxic effect in the systemic circulation
5) reduce the bleeding in the area of injection & improve visability at the surgical site.

Front 65

What happens if a LA doesn't include a vasoconstrictor?

Back 65

The drug is more quickly removed from the injection site and distributed into systemic circulation.

Front 66

Any anesthetic given w/o a vasoconstrictor is more likely to be _______ than those given with a vaso constrictor.

Back 66

Toxic

Front 67

What has been shown when using a 1:100,000 vs a 1:200,000 dose of epi as a vasoconstrictor?

Back 67

They produce about the same amount of vasoconstricton and the same distributon of local anesthetics.

Front 68

How long should a Pt who's had either an MI, or a stroke in the past ______ (length of time) wait to make an appt for elective dental Tx after their medical condition is under control?

Back 68

6 months

Front 69

What 2 epi drug interactions that are most likely to be clinically significant?

Back 69

1) Triccyclic antidepressants (not used too much)
2) Selective B-Blockers (Beta blockers)

Front 70

The duration of action is primarily related to the LA's _______ _________ capacity.

Back 70

Protein-binding

*Duration is unrelated to the local's half life.*

Front 71

___________ _________ determines the potency of a local anesthetic agent.

Back 71

Lipid solubility

Front 72

pKa is related to the _______ __ ________.

Back 72

duration of action.

*With lower pKa the LA is distributed more in the base for so its better absorbed.*

Front 73

____________, an ester, is the most commonly used topical anesthetic.

Back 73

benzocaine.

Front 74

__________, an amide is the 2nd most commonly used topical anesthetic

Back 74

lidocaine

Front 75

1000mg is equal to how many grams?

Back 75

1 gram

Front 76

1 gram is equal to how many milligrams?

Back 76

1000 mg's

Front 77

A 2% solution is equal to how many mg/ml?

Back 77

20mg/ml

Front 78

A 6% solution is equal to how many mg/ml?

Back 78

60mg/ml

Front 79

A 4% solution is equal to how many mg/ml?

Back 79

40mg/ml

Front 80

What is the equation to change lbs to kg?

Back 80

lbs/2 - 10% = the weight in kg (kilograms) *160lbs/2 -10% = 72kg

Front 81

100 mg is equal to ______ grams?

Back 81

0.1 grams

Front 82

In a 1% solution how many mg/ml?

Back 82

10 mg/ml