Exam 3: Local anesthetics Flashcards
What part of the pain pathway do local anesthetics work to block?
Prevent transmission of the pain
What is the distinguishing characteristic of local anesthetics?
ability to provide complete loss of all sensory modalities
What part of a neuron does a local anesthetic act to block?
sodium channels helping to carry an action potential down the axon
What are the three structural components of local anesthetics?
Hydrophobic component, intermediate linker component, hydrophilic component
What does the hydrophobic component of an anesthetic do?
Increases potency, plasma protein binding, increases duration of action, increases toxicity
What is usually the structure of the hydrophobic component of an anesthetic?
aromatic ring
What are the two linker classes of an anesthetic?
Ester bone and amide bond
What determines the metabolic fate of a local anesthetic?
the linker component (esters are rapidly broken down in plasma, esters have higher potential for allergic sensitization)
What are does the hydrophilic component of an anesthetic do?
determines the dissociation constant, impacts the onset of action
What is the structure of a hydrophilic component of an anesthetic usually?
An amine
Are local anesthetics weak acids or weak bases?
Weak bases, pK= 8-9
When are weak bases ionized, when are they un-ionized?
ionized in acidic environments, unionized in basic environments
What form (ionized or not) of an anesthetic can cross a cell membrane?
unionized
What form of an anesthetic (ionized or not) can act on the sodium channels to block them?
ionized
Do higher or lower pK drugs have a more rapid onset of action? Why?
Lower pK, more uncharged form of drug at physiological pH (more can enter the cell quickly)
What state of a sodium channel (resting, open, inactive) do drugs have an affinity for?
High affinity for open or inactive states, forcing them to stay in the inactive state
What nerves do local anesthetics preferentially block?
Nerves that have a higher rate of depolarization and smaller diameter, myelinated nerves before unmyelinated
What is the order in which sensations are affected with local anesthetics
Pain, cold, warmth, touch, deep pressure, motor function
T/F: LAs can increase vasodilation
True
What are adverse effects of LAs on CNS?
tongue numbness, dizziness, visual disturbances, tinnitus, slurred speech, convulsions, eventual coma
What are adverse effects of LAs on the cardiovascular system?
hemodynamic instability, decreased myocardial electrical excitability, cardiovascular collapse
What linker region is associated with hypersensitivity? why?
ester LAs because of para-aminobenzoic acid (PABA), which is a metabolite of esters
What is the absorption of LAs determined by?
dose, vascularity of target, drug tissue binding
What can be used to decrease systemic absorption of LAs?
epinepherine (vasoconstrictor), helps to keep a higher local concentration
What can affect local distribution of LAs?
pH of the local tissue- inflamed tissues and infection often have a lower pH
Where are esters and amides metabolized respectively?
esters in plasma by pseudocholinesterase, amides in liver by oxidases
What is EMLA?
Eutectic mixture of local anesthetics, exists as an oil at room temp so it penetrates in tact skin, effective for procedures such as lumbar punctures
What is infiltration anesthesia used for? What is its route?
Subcutaneous injection, used for minor surgery and dental procedures
What is a nerve block for? What is its route?
Injection at base of digit or larger volume into brachial plexus, Major or minor block of peripheral nerve conduction
What is a Bier block?
IV injection of anesthetic + tourniquet to keep it there, used to anesthetize distal arm or leg, used in forearm, hand, sometimes distal leg and foot
What is an epidural anesthesia?
Injection of LA into epidural space during labor and delivery, primarily acts on nerve roots, can go to blood so should use epinephrine to decrease peak plasma rates
What is spinal anesthesia?
Injection into CSF in lumbar space, can anesthetize large amount of body, the density of the solution determines where it moves (more dense, it’ll travel down to caudal spinal cord)
Describe procaine
Ester-type, short acting usually given with vasoconstrictor, rapid metabolism of plasma
Describe lidocaine
Amide-type, metabolized in liver, overdose may cause death from v-fib
Describe mepivacaine
Amide type, not effective topically, somewhat longer acting than lidocaine
Describe bupivacaine
Amide type, long acting and potent LA, used for: regional and epidural blocks, prolonged surgery
Describe ropivacaine
Amide-type, long acting LA, less CV and CNS toxicity than bupivacaine
Describe tetracaine
Ester-type, used for topical anestheisa of eye, nose and throat and for spinal anesthesia
Describe cocaine
ester-type, good penetration of tissues and its a vasoconstrictor, used for upper respiratory tract and mucosal membranes
