Exam 3: Local anesthetics Flashcards
What part of the pain pathway do local anesthetics work to block?
Prevent transmission of the pain
What is the distinguishing characteristic of local anesthetics?
ability to provide complete loss of all sensory modalities
What part of a neuron does a local anesthetic act to block?
sodium channels helping to carry an action potential down the axon
What are the three structural components of local anesthetics?
Hydrophobic component, intermediate linker component, hydrophilic component
What does the hydrophobic component of an anesthetic do?
Increases potency, plasma protein binding, increases duration of action, increases toxicity
What is usually the structure of the hydrophobic component of an anesthetic?
aromatic ring
What are the two linker classes of an anesthetic?
Ester bone and amide bond
What determines the metabolic fate of a local anesthetic?
the linker component (esters are rapidly broken down in plasma, esters have higher potential for allergic sensitization)
What are does the hydrophilic component of an anesthetic do?
determines the dissociation constant, impacts the onset of action
What is the structure of a hydrophilic component of an anesthetic usually?
An amine
Are local anesthetics weak acids or weak bases?
Weak bases, pK= 8-9
When are weak bases ionized, when are they un-ionized?
ionized in acidic environments, unionized in basic environments
What form (ionized or not) of an anesthetic can cross a cell membrane?
unionized
What form of an anesthetic (ionized or not) can act on the sodium channels to block them?
ionized
Do higher or lower pK drugs have a more rapid onset of action? Why?
Lower pK, more uncharged form of drug at physiological pH (more can enter the cell quickly)
What state of a sodium channel (resting, open, inactive) do drugs have an affinity for?
High affinity for open or inactive states, forcing them to stay in the inactive state
What nerves do local anesthetics preferentially block?
Nerves that have a higher rate of depolarization and smaller diameter, myelinated nerves before unmyelinated
What is the order in which sensations are affected with local anesthetics
Pain, cold, warmth, touch, deep pressure, motor function
T/F: LAs can increase vasodilation
True
What are adverse effects of LAs on CNS?
tongue numbness, dizziness, visual disturbances, tinnitus, slurred speech, convulsions, eventual coma
What are adverse effects of LAs on the cardiovascular system?
hemodynamic instability, decreased myocardial electrical excitability, cardiovascular collapse
What linker region is associated with hypersensitivity? why?
ester LAs because of para-aminobenzoic acid (PABA), which is a metabolite of esters
What is the absorption of LAs determined by?
dose, vascularity of target, drug tissue binding
What can be used to decrease systemic absorption of LAs?
epinepherine (vasoconstrictor), helps to keep a higher local concentration