Local anesthetics/amides/esters Flashcards
What are nociceptors?
Free nerve endings of primary afferent neurons
What is the difference between pain and nociception?
Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, whereas nociception is the detection of a noxious stimulus at the tissue level by nociceptors.
What are the 5 nociception pathways?
transduction, transmission, modulation, projection, perception.
What nociceptors are present on the distal terminus of primary sensory nerve fibers?
ABeta fibers, A-delta fibers, and C fibers
Which nociceptors are responsible for sensing “first pain”?
A-delta fibers
What is chronic pain?
pain that persists longer than is providing protection.
Neuron alteration occurs through which 2 main changes?
peripheral sensation and central sensitization.
What is hyperalgesia?
exaggerated perception of pain produced by a noxious stimulus.
What is allodynia?
non-noxious stimulus that elicits pain.
Where does central sensitization occur and what receptors does it involve?
It ooccurs in the dorsal horn of the spinal cord and involves NMDA receptors.
Does central pain sensitization occur in chronic and acute pain, or just chronic?
chronic and acute
What enables low intensity stimuli to produce pain?
changes in sensory processing in the spinal cord.
What receptor plays a central role in chronic pain?
NMDA
What is the result of increased glutamate in the synaptic cleft?
activates normally closed NMDA receptors.
What parts of the pain pathway are affected by local anesthetics?
transduction, modulation, and transmission.
Perception is affected by what type of anesthetics?
general anesthetics
What are the main effects of local anesthetics?
they cause the reversible blockade of transmission in peripheral nerves or spinal cord to stop pain signaling from progressing.
T/F: local anesthetics are any drugs that cause the reversible blockade of nerve impulse conduction when applied locally to nerve tissue.
True.
What are 2 classes of local anesthetics?
Amides and esters
T/F: all local anesthetics are weak acids.
False. They are weak bases.
What is the mechanism of action of local anesthetics?
neurologic blockade occurs by preventing depolarization and blocking the propagation of an action potential by inhibiting the influx of sodium through voltage-dependent Na+ channels.
How is the duration of action of local anesthetics usually terminated?
By redistribution.
What affects the onset of action of local anesthetics?
physiochemical properties, site of administration, and drug dose.
What affects the duration of action of local anesthetics?
lipophilicity, ability to bind the sodium channel, underlying disease, and drug to drug interactions.
Where are amides mainly metabolized?
liver
what breaks downs esters?
plasma esterases
T/F: amide local anesthetics have short half lives.
False. Their half life is long because they are metabolized by the liver.
What are some routes of administration for local anesthetics?
topical, local infiltration, or IV regional anesthesia
What are some examples of regional analgesia?
Brachial plexus block or an intercostal nerve block.
When would a wound soaker catheter be used?
After surgery requiring regional analgesia.
What are some contraindications of epidurals and epidural catheters?
coagulopathy, anatomy, skin infection/sepsis, and neurologic disease.
What are some complications/adverse effects of epidurals?
local irritation, CNS stimulation, CNS depression, cardiovascular depression, and other less common effects.
This drug is the most commonly used local anesthetic in vet med, has a rapid onset of action, and is metabolized by the liver.
Lidocaine.
About how long does it take lidocaine cream to take effect?
20-30 minutes.
Would you use epi with lidocaine when using lidocaine systemically?
No.
What other use does lidocaine have?
antiarrhythmic (ventricular arrhythmias)
T/F: lidocaine is used to stimulate intestinal motility in the horse.
True
This local anesthetic is potent, has a longer duration of action, and is the most cardiotoxic of the local anesthetics.
Bupivacaine.
When should you be weary of using bupivacaine?
in post-op pericardectomy patients.
How is bupivacaine infused?
through thoracostomy tubes or soaker catheters.
What is mepivacaine used for?
diagnosing nerve blocks in horses and for epidurals.
This drug is less irritating and has a longer duration of action than lidocaine, and is preferred for distal limb/intraarticular injections.
Mepivacaine.
This drug is an ester, is used topically, has a rapid onset, and allows for corneal and conjunctival manipulation.
Proparacaine.
T/F: proparacaine can be used intranasally for nasal-oral feeding tube placement.
True.
This ester is not used as a local anesthetic, but is a class 1a antiarrhythmic.
Procainamide
Is procaine used as a local anesthetic?
No, but it is present in some penicillin G preparations.
