Local Anesthetics Flashcards
Amides - list drugs:
- lidocaine
- articaine
- mapivacaine
- etidocaine
- prilocaine
- bupivacaine
- ropivacaine
- levobupivacaine
Esters - list drugs:
- procaine
- cocaine
- chloroprocaine
- tetracaine
- benzocaine
local anesthesia definition:
loss of sensation limited to a local area or region of the body
local anesthetic definition:
drug that blocks generation and propagation of nerve impulse that results in reversible, regional loss of function (analgesia)
local anesthesia advantages and disadvantages:
adv:
-drug is delivered directly to target organ - minimal loss of function=increased safety bc less disruption of organ systems
disadv:
-high concentration in small area may increase potential for systemic toxicity, poor min-min control and may not be adequate for procedure
Clinical uses for local anesthetics:
- topical
- perineural infiltration- need a lot of drug but easy to administer
- nerve block- less drug but needs to be skillful administered in a specific spot
- spinal block-into subarachnoid-large body area blocked but all areas distal to block are also useless - HYPOTENSION or could reach the brain
- epidural block- injection into extradural space- not in spinal canal yet blocks large area
Local anesthetics - MOA:
- *-blockade of voltage gated sodium channels
- decrease in generation and conduction of action potentials
- inh of Na and K conductance
- inh of depolarization and repolarization
Local anesthetics - sites of action:
- biotoxins (saxitoxins, tetrodotoxin) - EXTRACELLULAR PART - no man made drugs hit this site
- lidocaine (receptor theory) (INTRACELLULAR PART)
- benzococaine (uncharged) (IN LIPID BILAYER –> DISTURB GEOMETRY OF ION CHANNEL) (membrane expansion theory)
- combo lido and benzo (most clinically used
Two major Local anesthetic drug classifications?
amides
esters
figuring out which name is amide and which is ester?
- end in “-caine” suffix
- usually amides have 2 i’s in their name while esters have only 1 i.
Local anesthetic properties:
- weak bases - available as salts
- cationic form (LAH+) = msot active form at sodium receptor
- uncharged form (LA) = important for lipid penetration of membraness
- rapid absorption in highly vascular areas
- smaller and more lipophilic LAs are more potent, have faster rate of interaction with sodium channels and have longer duration of action
**Amides properties:
- *-longer halflife and longer duration of action
- half-life altered with liver issues
**Esters properties:
- short plasma half-life = short duration of action
- rapid metabolism by hydrolysis via butyrylcholinesterase (BChE)
- excreted in urine
Factors that influence LA onset and recovery of nerves - factors:
1) FIBER SIZE:
a) LAs block all nerves - not just nociceptors
b) smallest fibers most sensitive
c) myelinated more sensitive
d) blocking effect:
1st—–B (preganglionic, small, myelinated)
—–C (small, non-myelin–>slow pain and temp)
—–A-delta (medium, myelin–>fast pain, temp, crude touch)
—–A-gamma (medium, myelin–>muscle spindle)
—–A-beta (large, myelin - discriminative touch)
last—–A-alpha (motor, proprioception)
2) SITE OF DEPOSITION: anesthesia occurs first at the outer fibers as the drug moves down conc gradient
3) pH: inc pH = dec Cm (inc potency)
4) nerve stimulation rate: higher frequency nerves (Sensory) are more sensitive
5) Ca conc: Inc Ca = inc Cm (dec potency)
6) Addition of vasoconstrictors:
- epinephrine, phenylephrine, levonordefrin
- increase duration of action
- increase in local neuronal abs at site of drug administration
- vasoconstrictor substances reduce local blood flow and reduce systemic abs and toxicity
**minimum anesthetic concentration (Cm) =
=minimum concenration of drug for standard block
=relative standard of potency
