Local Anesthetics Flashcards
What is the definition of a local anesthetic?
It is a drug that blocks nerve conduction and generation of action potentials when applied to any part of the nervous system and on every type of nerve fiber, without loss of consciousness.
What is the prototype local anesthetic?
Procaine.
What is the most popularly used local anesthetic?
Lidocaine.
What was the first highly effective local anesthetic with reversible activity?
Cocaine.
What are some desirable characteristics of local anesthetics?
1) Should not be irritating or produce permanent damage.
2) Should not be addictive.
3) Low systemic toxicity.
4) Rapid onset.
5) Duration - sufficiently long to perform a diagnostic or surgical procedure.
6) Should be reversible.
What are three chemistry components of local anesthetic compounds?
1) Amine group.
2) Aromatic group.
3) Ester or amide linkage.
What does the amine group confer to the compound?
Confers HYDROPHILIC properties.
What does the aromatic group confer to the compound?
Confers HYDROPHOBIC (& lipophilic) properties.
What does the ester or amide linkage confer to the compound?
Determines route of metabolic degradation and potential allergic reactions.
What does the molecular size of the compound influence?
Influences rate of dissociation of local anesthetics from their receptor sites.
What are three common LA’s that have ester linkage?
1) Cocaine.
2) Procaine.
3) Tetracaine.
What common LA has an amide linkage?
Lidocaine.
How is absorption of a local anesthetic agent determined?
Determined by site of injection, dosage, presence of vasoconstricting agent and pharmacological profile of the local anesthetic itself.
What is pH critical for in terms of local anesthetics?
pH is critical for local anesthetics effectiveness.
What is the makeup of a local anesthetic and how are they marketed?
Local anesthetics are weak bases (only slightly soluble), marketed at HCl salts.
Why is cell penetration of a local anesthetic poor in infected and necrotic tissues?
Infected and necrotic tissues have a lower pH, consequently there will be a very low fraction in the unionized form and cell penetration will be poor.
What is the pH characteristic of?
The environment.
What is the pKa characteristic of?
The drug.
Local anesthetics are what _____ (acids or bases)?
Weak bases.
What would you dissolve local anesthetics in because they are weak bases?
Acids (commonly HCl).
At a low pH, local anesthetics are primarily what? Ionized or unionized?
Ionized.
If a local anesthetic is in a low pH and primarily ionized, what will it do physiologically?
Interaction with the receptor rather than facilitate crossing of the membranes.
A necrotic tissue is basic or acidic?
Slightly acidic compared to normal.
Does it take more or less time for necrotic tissues to be anesthetized?
More time.
What can be added to a local anesthetic to help prolong the effect?
Epinephrine or other adrenergenic compounds.
What three effects will adding epinephrine to the solution of local anesthetic cause?
1) Prolong drug duration by decreasing blood flow (local vasoconstriction).
2) Decrease systemic toxicity by slowing absorption.
3) Delay healing or cause local tissue necrosis or edema.
What is important in assessing the toxicity of local anesthetics?
The rate of metabolism and the metabolic by-products.
