Local Anesthetics Flashcards
Administration methods of local anesthetics
-topical -local/field -intravenous block -peripheral nerve -plexus (brachial, lumbar) -central neuralgia (epidural, spinal)
Which has a longer half life, mepivacaine or lidocaine?
Mepivacaine (> 1 hr)
Define frequency-dependent block
Local anesthetics require the Na+ channel to be open in order to block it; thus, the greater the activity of he nerve, the greater the chance it will be blocked
What is the duration of a local anesthetic dependent on?
How well it penetrates the axoplasm and reaches the Na+ channel
Lidocaine
Classification: local anesthetic & antiarrhythmic
MOI: blocking of Na+ channels
Uses: local and topical anesthetic, occasionally used to treat ventricular arrhythmias
Contraindications: known sensitivity to drug class, Adams stokes syndrome, severe SA, AV, or intraventricular heart block
Adverse effects: dose-related, CNS depression
Administered: IV, SC
Cross BBB? Yes
Elimination: metabolized by liver
Define local anesthetic
Drug that produces “reversible loss of sensation in an area of an animal’s body without loss of consciousness or alteration of CNS activity”
Mepivacaine
Classification: local anesthetic MOI: blocking of Na+ channels Uses: preferred local anesthetic used in horses: spinal, laryngeal, lower leg & intrathecal use Contraindications: known sensitivity to class of drugs, heart block Adverse effects: dose-related, CNS depression, cardiotoxicity, tissue edema at site of injection Administered: SC Cross BBB? Yes Elimination: metabolized by liver
What are the two types of local anesthetics?
Amino amides (most common) Amino esters (degraded by enzymes- plasma esterases)
If there is an “i” before the caine, the drug is an amide or ester?
Amide (e.g. Lidocaine, Bupivacaine, Mepivacaine)
Why is Bupivacaine not advised to be administered IV?
Due to cardiotoxicity
What is the general structure of most anesthetics?
Lipophilic end and hydrophilic end
The amount of local anesthetic that reaches the blood depends on which 4 things?
- The site of injection
- presence/absence of vasoconstrictors, the physical property of the drug, and the amount injected
Methemglobinemia is a rare potential side-effect of what local anesthetic?
Lidocaine
What is the effect of protein plasma binding on the effects of a local anesthetic?
If absorbed from the injection site into circulation, the drug must be free and non ionized
What is the mechanism of action of anesthetics?
They target sodium channels in excitable cells (Nav1 and Nax) and block conduction of these nerves (block action potential/pain signal)
Why are unmyelinated and thinly myelinated axons the major targets of anesthetics?
Because these are the axons that generate/carry pain signals
Bupivacaine
Classification: local anesthetic MOI: blocking of Na+ channels Uses: local anesthetic, spinal & intrathecal use Contraindications: known sensitivity to class of drugs, heart block Adverse effects: dose-related, CNS depression, cardiotoxicitiy (> than lidocaine) Administered: SC, intrathecal, spinal Cross BBB? Yes Elimination: metabolized by liver
True or False? Cocaine was the first utilized topical anesthetic in human medicine
True
What is the name of the local anesthetic restricted to ophthalmic use?
Proparacaine
What is the onset of action?
Time the local anesthetic takes a to produce blockade; dependent upon placement of drug, molecule, size, and pKa
True or false? In order for local anesthetics to work, the sodium channel must be open
True
Describe methemoglobinemia
-iron in hemoglobin is stabilized in ferric (Fe3+) form > O2 is unable to bind, results in hypoxia and death - Lidocaine is an oxidizer -can treat w/ methylene blue
Unmyelinated axons are affected more/less quickly than the larger myelinated fibers?
More
What is the potency of a local anesthetic related to?
Lipid solubility & pKA > promote penetration of drug to site of action
What two systems do local anesthetics have effects on?
CNS (depression) and cardiovascular (decrease in force of contraction)
The adverse effects to local anesthetics observed in patients are correlated to what?
The amount/concentration of the dose of local anesthetic given
For myelinated nerves, at least ____ nodes of Ranvier must be blocked to produce the effect?
Two
