Duan: Local anesthetics Flashcards
Do local anesthetics cause a loss of consciousness?
no
What do local anesthetics do?
block axonal conduction in nerves when applied in appropriate concentrations
Local anesthetics have a completely (blank) reaction
reversible
What drug was discovered in 1860 by German chemist Albert Niemann?
cocaine
**made his tongue feel numb
What did Sigmund Freud do with cocaine?
used it to treat morphine addiction
What did Carl Koller (ophthalmologist) do with cocaine?
used it as the first local anesthetic on glaucoma patients
What happened to Von Anrep, Freud, and Koller as a result of self-experimentation w cocaine?
they became addicted
Cocaine is an (blank) that is a potent (blank) stimulant
ester; CNS
Cocaine is a potent sympathomimetic and (blank)
vasoconstrictor
What unfortunate events can cocaine cause?
fatalities from arrhythmias (v fib), MI, or seizures
the first synthetic local anesthetic drug (1898), derivative of cocaine, slow onset , short duration, less potent, higher potential to cause allergic reactions, sympathomimetic (release adrenaline) increase heart rate, feel nervous
Procaine (Novocaine)
slightly more potent with shorter duration of action than procaine
Chloroprocaine (Nesacaine)
10 times more potent with slower onset and longer duration of action than procaine
Tetracaine (Pontocaine)
does not contain the terminal hydrophilic amine group, only slightly soluble in water, slowly absorbed with prolonged duration
Benzocaine
What is unique about Benzocaine?
it is only useful as a topical anesthetic
List 4 ester local anesthetics and the duration of action/potency
cocaine - medium duration, potency =2
procaine - short duration, potency =1
tetracaine - long duration, potency =16
benzocaine **surface use only
Lidocaine is an (blank) with execellent potency (2-3x more potent that procaine)
amide
What should lidocaine be combined with to increase its duration of action?
epinephrine
What is lidocaine used for?
surface anesthesia peripheral nerve block infiltration anesthesia spinal anesthesia epidural anesthesia antiarrhythmia
This is an amide that is pharmacologically similar to lidocaine; it is coadministered w epi to prolong duration of action
Mepivacaine
What is mepivacaine used for?
cardiovascular disease in elderly patients
What is unique about mepivacaine?
not useful in obstetrics bc of prolonged metabolism in fetus and neonate, which increases toxicity risk
This is an amide that is 10x more potent than procaine and has a particularly LONG duration of action (24hrs)
Bupivacaine
This is an amide with duration of action similar to bupivacaine, but slightly less potent
Ropivacaine
What is the mechanism of action of local anesthetics?
block voltage-gated Na+ channels in neuronal membranes that are responsible for signal propagation - the postsynaptic membrane will not depolarize and will thus fail to transmit an AP
How is specificity of anesthetics obtained?
by route of administration
**highly effective analgesia (loss of pain sensation) in well-defined regions
Which nerves should be blocked first?
small-diameter, unmyelinated nerve fibers
large-diameter, myelinated fibers less susceptible and require greater doses to achieve neural blockade
What is more important to consider with nerves, size factor or myelination?
size factor
Rank the following in terms of predominant nerve blockage:
small myelinated fibers
small unmyelinated fibers
large myelinated fibers
small unmyelinated > small myelinated > large myelinated
What is the order of sensory loss of the following?
touch
pressure
pain
temp
pain (lost first) > temp > touch > pressure (lost last)
What are 3 routes of administration for anesthetics?
regional: injected into area of nerve fibers to be blocked
topical: surface use; esp on mucous membranes
infiltration: inject under skin (often used with epinephrine to cause vasoconstriction)
When you get give anesthesia via an infiltration method (injected under skin), what should it be given with?
epinephrine
**causes vascular constriction
Where is spinal vs epidural vs caudal anesthesia injected?
spinal: subarachnoid space
epidural: outside of subarachnoid space, diffuses into subarachnoid space
caudal: epidural space of the sacral canal
What procedures usually require a spinal anesthetic? Where is it injected?
upper-abdominal surgery; injected into subarachnoid space
What procedures usually require a caudal anesthetic? Where is it injected?
perinea and rectal procedures; injected into epidural space of sacral canal
What are epidurals usually used for? Where is it injected?
ob: labor and delivery, C-section; administered outside, but diffuses into subarachnoid space
What are three factors that affect the reaction of local anesthetics?
lipid solubility: the higher the lipid solubility, the faster nerve penetration, and onset of action
pH influence: all local anesthetics are weak bases - decreased pH shifts equilibrium toward ionized form, which delays the penetration of the drug
blood flow: vasoconstrictors (epi) are used to limit the vasodilation activity of local anesthetics
What is the pH equation we should be aware of?
log(ionized/uncharged form) = pKa - pH
What is the pH of all local anesthetics?
weak bases (pH 8-9)
What does a decrease in pH do to onset of action of local anesthetics?
shifts the equilibrium to ionized form, delaying penetration of the drug and onset of action
Why would you want to vasoconstrict when giving local anesthetics?
to keep the drug around longer and delay the systemic absorption of the drug into the bloodstream
Which anesthetics, esters or amides, are very rapidly hydrolyzed in blood
esters
Hydrolysis of esters yields (blank)
paraaminobenzoic acid (PABA)
almost completely biotransformed in liver by amidases and undergo N-dealkylation followed by hydrolysis by liver microsomal cytochrome P450
amides
**pts with liver disease or taking other drugs affecting cyto P450 will reduce the biotransformation of amides
What do moderate doses of anesthesia do to the CNS? What do very high doses do to the CNS?
stimulate CNS; depress CNS
What affects do anesthetics have on the cardiovascular system?
depress myocardium
reduce excitability
lower contractility
slow conduction
Which anesthetic causes vasoconstriction?
cocaine
Which anesthetics have the highest rate of hypersensitivity reactions?
esters, bc they form PABA which is known to be allergenic
What is the most common cause of toxicity w anesthetics?
high dose and systemic concentration due to unintentional intravenous injection
What are three toxic affects we should be aware of when administering anesthesia?
cardio toxicity
allergic reaction
neurotoxicity