local anesthetics Flashcards
What is the definition of local anesthetics?
Loss of sensation in a circumscribed area of the body caused by depression of excitation in nerve endings or inhibition of the conduction process in peripheral nerves.
Most commonly used drug class in dentistry
Local Anesthetics
- Limited, defined area
- Awake, conscious patient
- Routes of administration
– Topical
– Injection
General Anesthetics
- Body-wide
- Unconscious patient
- Routes of administration
– Inhalation
– Injection
What properties are desired in a local anesthetic?
- Non-irritating to local tissue
- Should not permanently alter nerve structure
- Low systemic toxicity
- Efficacious when injected into tissue or applied locally to mucous membranes
- Rapid onset
- Suitable duration of action for the procedure
Name the three chemical components of local anesthetics and their primary functions
- Lipophilic domain: influences potency
- Intermediate chain: influences metabolism
- Hydrophilic domain: influences solubility
What are the 2 main types based on intermediate chain?
– Esters (e.g., procaine)
– Amides (e.g., lidocaine)
What is the action potential?
how neurons communicate with one another through neurotransmission, which is based on changes in electrical current in the cell membrane.
How do local anesthetics work to block pain?
– Penetration of nerve fiber
– Bind to target site
– Block sodium channels
– Decrease the rate of electrical depolarization
What happens upon administration of a local anesthetic with adequate anesthesia?
– Action potentials can’t occur
– No transmission of pain signals
What happens after the injection of a local anesthetic?
The anesthetic salt separates into base and cationic species.
What does the base species of a local anesthetic do?
penetrates tissue to reach the target site.
What does the cationic species of a local anesthetic do?
binds to the target site, blocking sodium flow through sodium channels.
What does the pKa value represent in terms of base and cationic species?
pH at which the cationic and base species are equal.
How does pKa affect tissue penetration by local anesthetics?
determines the proportion of base species that can penetrate tissue.
How does a lower pKa affect the base species in local anesthetics?
more base species are present to penetrate the nerve fiber, leading to a more rapid onset.
How does inflammation impact the pH at the affected area?
decreases the pH at the affected area, which leads to fewer base species being available.
Why should you choose a local anesthetic with a lower pKa?
ensures more base species are available for adequate anesthesia
What are the physiochemical properties?
- Potency
- Onset of action
- Duration of action
As ___________ increases, so does potency
lipid solubility
How does fiber diameter affect the onset of action of local anesthetics?
Smaller fibers lead to a quicker onset of action.
How does myelination affect the onset of action of local anesthetics?
Myelinated fibers result in a quicker onset of action.
How does pKa influence the onset of action of local anesthetics?
A lower pKa means a faster onset of action because more base species are available to penetrate the nerve.
What primarily determines the duration of action of a local anesthetic?
The amount of bound protein; higher protein binding results in a longer duration of action.
How are ester-based local anesthetics metabolized?
Primarily metabolized by plasma pseudocholinesterase, with some liver metabolism.
How are amide-based local anesthetics metabolized?
Primarily metabolized by the liver.
Both classes are primarily excreted by the kidneys.
List the determinants of toxicity
- Drug
- Concentration
- Route of administration
- Rate of injection
- Vascularity of tissue
- Patient’s weight
- Rate of metabolism and excretion
Which class of local anesthetics is most likely to produce allergenic toxicity?
Ester-based anesthetics
What is the likely cause of allergenic toxicity from ester-based anesthetics?
Typically due to a metabolite of esters, PABA
What are the symptoms of systemic toxicity of local anesthetics?
- CNS: Tremors, twitching, convulsions, respiratory depression, respiratory failure.
- Cardiovascular: Decreased neuronal excitability, conduction speed, and force; vasodilation, hypotension, cardiovascular collapse.
What is methemoglobinemia?
occurs when oxygen-providing hemoglobin (Fe++) is converted to the non-oxygen providing form (methemoglobin; Fe+++).
Which local anesthetic is most commonly associated with methemoglobinemia and how is it treated?
Most commonly associated with prilocaine (3-4 hours post-treatment).
Treatment: Methylene blue (IV) to reverse the condition.
Symptoms include cyanosis.
What is the benefit of adding a vasoconstrictor to some local anesthetics?
– Increased duration of action
– Decreased risk of toxicity
– Decrease in bleeding from surgical procedures
What are some contraindications for using vasoconstrictors in local anesthetics?
High blood pressure
Recent myocardial infarction
ASA 4+ patients
Tricyclic antidepressants use
Short-acting Local Anesthetics
- Cocaine
- Procaine
What type of local anesthetic is cocaine?
Cocaine is an ester local anesthetic.
What is the onset and potency of cocaine?
Cocaine has a short onset of action and moderate potency
What is the main clinical use of cocaine in modern medicine?
limited applicability, primarily used in ophthalmological procedures.
Does cocaine have vasoconstrictive properties?
Yes, cocaine acts as a vasoconstrictor.
What type of local anesthetic is procaine(novocain)?
Procaine is an ester local anesthetic.
What is the onset and duration of action for procaine?
Procaine has a long onset of action and a short duration of action.
How does the potency of procaine compare to other local anesthetics?
Procaine has low potency compared to other local anesthetics.
Intermediate-acting Local Anesthetics
- Lidocaine
- Articaine
- Mepivacaine
- Prilocaine
What type of local anesthetic is lidocaine (Xylocaine, Lignospan,Octocaine)?
Lidocaine is an amide local anesthetic.
Why is lidocaine typically combined with a vasoconstrictor?
counteract its vasodilating effects, unless the vasoconstrictor is contraindicated.
What is the onset of action for lidocaine?
short onset.
How potent is lidocaine compared to other local anesthetics?
moderate potency.
What is the systemic toxicity and allergic reaction risk of lidocaine?
low
How does the onset of action of articaine (Zorcaine, Septocaine) compare to other local anesthetics?
short onset of action.
What is the potency of articaine?
moderate potency
What is mepivacaine onset/duration of action and potency?
Moderate onset of action, duration and potency
What is Prilocaine onset/duration of action and potency?
Moderate onset of action, duration and potency
Methemoglobinemia is at greatest risk with?
Prilocaine
Long-acting Local Anesthetics
- Bupivacaine
- Etidocaine
What type of local anesthetic is Bupivacaine, etidocaine, Prilocaine, and Mepivacaine?
Amide
What is Bupivacaine onset/duration of action and potency?
longer onset/duration of action, high potency
What is Etidocaine onset/duration of action and potency?
- Short onset of action
- Long duration of action
- High potency
What is OraVerse used for?
reversal of soft-tissue anesthesia.
What is the active ingredient in OraVerse?
phentolamine mesylate.
What is the mechanism of action of OraVerse?
non-selective alpha adrenergic antagonist that produces vasodilation, improving blood flow at the injection site.
How long does it typically take for OraVerse to restore sensation?
1 hour
What are the disadvantages of using cocaine as a local anesthetic?
Cocaine increases the effects of local anesthetics, which might lead to intoxication.
