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Flashcards in Local Anesthetics DSA Deck (51):
1

What are local anesthetic drugs?

Atricaine
Benzocaine
Bupivacaine
Chloroprocaine
Cocaine
Dibucaine
Levobupivacaine
Lidocaine
Mepivacaine
Procaine (Novocain)
Proparacaine
Ropivacaine
Tetracaine

2

Describe general binding and action of local anesthetics

Local anesthetics bind reversibly to sodium channels in nerves and block ion movement through channel pore, blocking action potentials responsible for nerve conduction

When applied locally to nerve tissue in appropriate concentrations, they can act on any part of the nervous system and on every type of nerve fiber

A local anesthetic in contact with a nerve trunk can cause both sensory and motor paralysis in the area innervated

Since the development of the first drug in 1905 (procaine), local anesthetics have been used for both systemic and local effects

3

Which local anesthetics are amides?

Lidocaine
Mepivacaine
Bupivacaine
Ropivacaine
Articaine

4

Which local anesthetics are esters?

Benzocaine
Cocaine
Procaine
Tetracaine
Ester-types only have one "i," while amide-types have at least 2 "i's"

5

Which local anesthetics have medium duration of action?

Lidocaine
Mepivacaine
Articaine
Cocaine

6

Which local anesthetics have long duration of action?

Bupivacaine
Ropivacaine
Tetracaine

7

Which local anesthetics have a short duration of action?

Procaine

8

Which local anesthetic is used for surface use only?

Benzocaine

9

Compared to procaine which has a potency of 1, which local anesthetics have a potency of 16?

Bupivacaine
Ropivacaine
Tetracaine

10

Which local anesthetic has a potency of 4?

Lidocaine

11

Which local anesthetics have a potency of 2?

Mepivacaine
Cocaine

12

What is the chemistry of local anesthetics?

Typical local anesthetics contain both hydrophilic (amine) and hydrophobic (aromatic ring) moieties that are separated by an ester or amide linkage.

Those with ester linkages (benzocaine, cocaine, procaine, tetracaine) are more prone to hydrolysis than those with amide links (lidocaine, mepivacaine, bupivacaine, ropivacaine, articaine), and as a result, generally have a shorter duration of action

13

Describe absorption and distribution of local anesthetics

Dosage, site of injection, drug-tissue binding, local blood flow, use of vasoconstrictors, and physiochemical properties of local anesthetics all play a role in determining systemic absorption

The use of vasoconstrictor substances (epinephrine) will reduce systemic absorption of agents and are useful for drugs with intermediate or short durations of action

14

How is cocaine unique concerning absorption/distribution?

It is unique due to its intrinsic sympathomimetic vasoconstrictive properties

15

Compare distribution of amide local anesthetics with ester local anesthetics

Amide local anesthetics are widely distributed after intravenous bolus administration, while tissue distribution of ester-type agents have not been extensively evaluated due to their extremely short plasma half-lives

16

Describe the metabolism and excretion of local anesthetics

Ester-type agents are metabolized in plasma, while amide-type agents are metabolized in liver and then excreted in urine as charged substances

Ester-type compounds are hydrolyzed by circulating butyrylcholinesterase enzymes (plasma cholinesterase)

Amide linkage of amide-type agents are hydrolyzed by liver cytochrome P450 enzymes. Toxicity from these is more likely to occur in patients with hepatic disease

17

Describe the mechanism of action of local anesthetics

They block voltage-gated sodium channel currents and stop the spread of action potentials across nerve axons (receptor site for local anesthetics is at the inner vestibule of sodium channel)

They block nerve conduction by decreasing or preventing the large transient increase in permeability of excitable membranes to sodium that normally is produced by a depolarization of membrane

18

Describe the structure and activity of local anesthetics

The smaller and more lipophilic the local anesthetic, the faster the rate of the interaction with the sodium channel and the more potent the agent's actions

Ex: Tetracaine, bupivacaine, and ropivacaine are more lipophilic than lidocaine, procaine, and mepivacaine and are therefore more potent and have longer durations of action

19

Describe fiber diameter

Local anesthetics preferentially block small fibers because the distance over which such fibers can passively propagate an electrical impulse is shorter

Myelinated nerves tend to become blocked before unmyelinated nerves of the same diameter, so preganglionic B fibers are blocked before the smaller unmyelinated C fibers

20

Describe firing frequency

Fibers that fire at higher frequencies of depolarization are blocked before those that fire slower

Ex: Type A delta and C fibers are blocked earlier than large A alpha fibers

21

Describe fiber position

In bundles of large mixed nerves in large nerve trunks, it is not uncommon for motor nerve block to occur before sensory block because motor nerves are usually located circumferentially (motor nerves are the first nerves to be exposed to local anesthetic when it is administered into tissue surrounding the nerve)

In extremities, proximal sensory fibers are located in outer portion of nerve trunk and distal sensory innervation is located in core of nerve

22

Describe function, diameter (um), myelination, and sensitivity block for Type A alpha fibers

Proprioception, motor
12-20
Heavy
+

23

Describe function, diameter (um), myelination, and sensitivity block for Type A beta fibers

Touch, pressure
5-12
Heavy
++

24

Describe function, diameter (um), myelination, and sensitivity block for Type A gamma fibers

Muscle spindles
3-6
Heavy
++

25

Describe function, diameter (um), myelination, and sensitivity block for Type A delta fibers

Pain, temperature
2-5
Heavy
+++

26

Describe function, diameter (um), myelination, and sensitivity block for Type B fibers

Preganglionic autonomic

27

Describe function, diameter (um), myelination, and sensitivity block for Type C dorsal root fibers

Pain
0.4-1.2
None
+++++

28

Describe function, diameter (um), myelination, and sensitivity block for Type C sympathetic fibers

Postganglionic
0.3-1.3
None
++++

29

What are topical routes of administration?

Nasal mucosa, wound margins, GU tract, EENT

30

Describe infiltration anesthesia

Injection of local anesthetic directly into tissue in vicinity of peripheral nerve endings without taking into consideration the course of cutaneous nerves

Can be superficial enough to include only the skin and deep enough to include intraabdominal organs

31

Describe block anesthesia

Injections of local anesthetics in major nerve trunks
Purpose is to anesthetize a region distal to site of injection
Ex: femoral nerve block for surgery distal to knee, brachial plexus block for procedures on upper extremities or shoulders

32

Describe spinal anesthesia

Injection of local anesthetic into cerebrospinal fluid in lumbar space
Produces anesthesia over a considerable fraction of body with a dose of local anesthesia that produces negligible plasma levels

33

Describe epidural anesthesia

Injection of local anesthesia into epidural space
Can be performed in sacral hiatus or in lumbar, thoracic, or cervical regions of spine
Current popularity has arisen from development of catheters that can be placed into epidural space, allowing their continuous infusions or repeated bolus administration

34

Describe intravenous regional anesthesia (Bier block)

Used for short surgical procedures (

35

Describe prolongation of action by vasoconstrictors

Duration of local anesthetic action is proportional to time in contact with nerve
Coadministration of local anesthetics and vasoconstrictors (epi to activate alpha-adrenergic receptors and cause vasoconstriction) decreases the rate of anesthetic absorption into circulation, reduces rate at which local anesthetic is metabolized, and reduces systemic toxicity

36

Describe epinephrine action of prolongation

Epinephrine-containing solutions should not be injected into tissues supplied by end arteries (fingers, toes, ears, nose, penis) because the resulting vasoconstriction may cause gangrene

Use caution when injecting epinephrine-local anesthetic combinations into muscle tissue (epi can activate beta2-adrenergic receptors in skeletal muscle vascular beds and cause dilation, increasing potential for systemic toxicity)

37

Describe cocaine and prolongation by vasoconstrictors

Cocaine alone potentiates effect NE on alpha-adrenergic receptors by blocking NE transporter and results in localized vasoconstriction, eliminating need for combining drug with epi

38

What are the two major forms of local anesthetic toxicity?

Systemic effects following absorption of local anesthetics (CV or CNS effects)
Direct neurotoxicity from local effects of these drugs when given in close proximity to spinal cord and other major nerve trunks

39

Describe undesired effects of local anesthetics on CNS

Low concentrations have the ability to produce sleepiness, light-headedness, visual and auditory disturbances, and restlessness (early signs of toxicity include circumoral and tongue numbness and metallic taste)

High concentrations may result in nystagmus (unintentional jittery movement of eyes), muscle twitching, and convulsions

Central stimulation is followed by depression. Death usually is caused by respiratory failure

40

When large doses of a local anesthetic are required, premedication with ____ can provide prophylaxis against CNS toxicity. How?

Benzodiazepine (diazepam or midazolam)
Raising seizure threshold (local anesthetics cause depression of cortical inhibitory pathways, thereby allowing unopposed activity of excitatory neuronal pathways)

41

Describe undesired effects of local anesthetics on CV system

Result of direct effects on cardiac and smooth muscle and from indirect effects on autonomic nervous system
Local anesthetics block cardiac sodium channels and decrease electrical excitability, conduction rate, force of contraction, and arteriolar dilation, leading to systemic hypotension (not the case with cocaine)

42

Describe cocaine effects on CV system

Inhibits NE reuptake and results in vasoconstriction (which can lead to local ischemia), hypertension, and cardiac arrhythmias

43

Describe bupivacaine effects on CV system

Most cardiotoxic due to its long durations of action

44

Describe lidocaine effects on CV system and CNS

Class Ib antiarrhythmic
Suppresses automaticity of conduction tissue by increasing electrical stimulation threshold of ventricle, His-Purkinje system, and spontaneous depolarization of ventricles during diastole by a direct action of tissues
Blocks both initiation and conduction of nerve impulses by decreasing neuronal membrane's permeability to sodium ions, which results in inhibition of depolarization with resultant blockade of conduction
Most common adverse effect of IV lodicaine is CNS toxicity, which is typically mild, dose-dependent, and always resolves upon discontinuation

45

Describe allergic reactions to local anesthetics

Allergic reactions to ester-type local anesthetics are most common due to metabolism to allergy-causing compounds (allergies to amide-type local anesthetics are extremely rare)

Pts who are allergic to one ester-type agent will most likely be allergic to another ester-type

46

Describe benzocaine

Poor solubility in water, used only as a topical agent
Used topically for dermatologic conditions, hemorrhoids, premature ejaculation, and as an anesthetic lubricant (nasogastric and endoscopic tubes and catheters)

47

Describe bupivacaine

Agent with long duration of action capable of producing prolonged anesthesia
Has a tendency to provide more sensory block than motor block

48

Describe cocaine

Clinically desired properties are blockade of nerve impulses and local vasoconstricting actions secondary to its ability to inhibit local NE reuptake
Euphoric properties are primarily due to inhibition of catecholamine reuptake (mainly dopamine in CNS)
Used primarily as a topical anesthetic of upper respiratory tract

49

Describe dibucaine

Due to toxicity associated with injections, now used only as a topical cream for use on skin

50

Describe lidocaine

Prototypical amide local anesthetic
Alternative choice for individuals sensitive to ester-type local anesthetics
Produces faster, more intense, longer lasting, and more extensive anesthesia than an equal dose of procaine
Used as an antiarrhythmic agent

51

Describe procaine

Compared to newer agents, procaine generally has lower potency, slower onset, and shorter duration of action
Only used for infiltration anesthesia (local anesthesia produced by injection of solution directly into area of terminal nerve endings)
Metabolized to a para-aminobenzoic acid, which inhibits action of sulfonamide antibiotics