LA in Dentistry Flashcards
1
Q
LA Chemical properties
A
- Most are amphiphilic
- both lipophilic and hydrophilic
- LA without a hydrophilic part as used as topical agents (benxocaine)
- LAs are either esters or amides
- Esters are outdated (novacaine)
- Most common LA are amides (Lidocaine)
2
Q
LA Characteristics (acid/base chemistry)
A
- Basic compounds
- Poorly soluble in water
- Unstable in air
- pKa values range from 7.5-10
- Bc basic, combine with acids to form salts
- Salt form makes them soluble and stable in water or saline
- Why Lidocaine HCL on package
3
Q
How do LA work
A
- Enters from inside the cell
- Blocking the sodium channels which inhibits the depolarization of the membrane
- LA bind to specific receptors on the sodium channel
- Thereby stopping the impulse from continuing down the axon
4
Q
pH effects on LA
A
- the pH of anesthetic (and pH of tissue) influences its nerve blocking action
- Acidification (lower pH) of tissue decreases effectiveness of LA (inflammation and infection)
- Inflammed tissue pH 5-6
5
Q
LA in equilibrium
A
- LA exists simultaneously as uncharged molecules RN base, and positively charged RNH+ (cation)
- RNH+ + = RN + H+
6
Q
LA acid/base in low pH
A
- Equilibrium shifts to the left
- Most of the anesthetic exists in cationic form and can’t diffuse into sodium channels and bond to a receptor protein
- RNH+ > RN + H+
7
Q
LA acid/base High pH
A
- Equilibrium shifts toward the free base form
- Can diffuse into sodium channels and bind receptor proteins
- RNH+ < RN + H
