13 Flashcards
(25 cards)
Postitively charged anesthetic will
act once it gets inside neural membrane. Both form of anesthetics exist, and amine groups help get pKa to 7.4 where we want these to be working.
**basic form does a better job of getting in the membrane than acidic form generally speaking. Both act, but the basic form gets in better.
Ester linkages ——- better than amide
break apart - serum cholinesterases will hydrolyze esters
Aromatic groups are for
lipophilic properties - crossing membranes.
Do NOT inject these things into
arteries - they will get into the brain.
Esters downsides
hydrolyzing leads to something being more allergenic - the hydrophobic group is allergenic.
Local anesthetics with an ester linkage will be hydrolyzed by
pseudocholinesterase and have a very short half life in the plasma
Local anesthetics with an amide linkage will be metabolized by
P450 enzymes in the liver and have a longer half life in the plasma.
Esters are more generally
allergenic
Amides will have an
I in their name prior to the “caine”
Local anesthetics favored in dentistry are
amides
Local anesthetics cross the axon membrane and interact with the ————— forms of the Na+ channel, blocking Na+ conductance. They are not effective outside the axon.
open and inactivated
Because local anesthetics bind to the open form of the sodium channel, they produce a more
rapid nerve block on axons with a more rapid firing rate.
- Functions served by ——— are more readily disrupted by local anesthetics than the —————
B and C fibers
motor functions served by (larger) A fibers*
- Sensory neurons are ———–in size and sensitivity
heterogeneous
The faster a fiber is blocked, the ——- it takes to recover
longer - first on first off.
Block more
rapid with rapidly firing nerves
Inflamed tissue is more difficult to anesthetize.
Products released by cells in inflamed tissue lower
pH, making it more difficult to get sufficient levels of anesthetic inside the axon.
If epinephrine is included, the pH is frequently lowered to ——– to stabilize the epinephrine.
4 or 5
The buffering capacity at the injection site should ————-
neutralize this lower pH from stabilizing epinephrine
Risk of adding bicarbonate before injection?
precipitating anesthetic.
Direct effects on the heart local anesthetic.
Block cardiac Na+ channels Block cardiac Ca++ channels (much higher concentrations)
Effects on the autonomic nervous system: (inhibition of sympathetic responses)
Depress contractility, produce hypotension
-zosin
a1-adrenergic receptor blocker
-olol
b-adrenergic receptor blocker
