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xPharm Exam 2 > Local Anesthetics > Flashcards

Local Anesthetics Flashcards

1
Q

Chemistry (7)

A
  • Weak bases 8-9 (charged: cationic)
  • To penetrate membranes must be uncharged
  • Much less effective in infected tissue (such as an abscess) due to lower tissue pH, unable to diffuse into cell
  • Local anesthetic receptor isn’t accessible from external side of cell membrane
  • Most have a lipophillic group attached to an ionizable group by an ester or amide bond
  • Esters have shorter DOA (more prone to hydrolysis)
  • Stereochemical configurations are important
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2
Q

Esters (4 drugs)

A
  • Cocaine
  • Procaine (Novocain)
  • Tetracaine
  • Benzocaine
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3
Q

Amides (5 drugs)

A
  • Prilocaine
  • Etidocaine
  • Lidocaine
  • Mepivacaine
  • Bupivacaine

PELM B

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4
Q

Local Anesthetics: General (6)

A
  • Reversible
  • Block voltage-gated sodium channels
  • Blocks pain sensation from sympathetic vasoconstrictor impulses to specific areas of the body
  • Delivered directly to target organ
  • Systemic circulation serves only to diminish or terminate effects
  • Routes: topical, injection and instillation (within epidural or subarachnoid spaces)
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5
Q

Local Anesthetics: Absorption (2)

A
  • Systemic absorption from injected local at site of administration
  • Can be modified by: dosage, site, drug-tissue binding, presence of vasoconstricting substances, physiochemical properties of the drug
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6
Q

Local Anesthetics: Distribution (5)

A
  • Amide locals are widley distributed aver IV bolus
  • Esters have such short DOA they aren’t studied
  • Initial rapid distribution phase, then slower redistribution
  • Sequestration occurs in storage sites (fat)
  • At nerver fiber leve, only small fraction penetrates fiber
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7
Q

Local Anesthetics: Metabolism and Excretion (4)

A
  • Converted in liver or plasma to water-soluble metabolites and then excreted in urine
  • Acidification of urine will increase ionization of base to water soluble compunds which are more readily excreted
  • Esters are hydrolyzed very rapidly in blood by butyrylcholinesterase (pseudocholinesterase), so have very short plasma T1/2s (less than 1 min)
  • Amides are hydrolyzed by CYP450, toxicity can occur in those with liver disease
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8
Q

Rate of liver metabolism from fastest to slowest:

A
  • Prilocaine
  • Etidocaine
  • Lidocaine
  • Mepivacaine
  • Bupivacaine
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9
Q

Action Potential Review (4)

A
  • During excitation, Na channels open and a fast inward Na current depolarizes membrane toward Na equilibrium potential
  • This depolarization causes Na channels to close and K channels to open
  • Outward flow of K repolarizes the membrane toward K equilibrium potential
  • This repolarization brings Na channels back to rested state
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10
Q

MOA of Local Anesthetics (6)

A
  • Work to block voltage-gated sodium channels (if blocked over a critical length of the nerve, propagation across the are is no longer possible… no conduction)
  • When progressively increasing concentrations of LA are applied to a nerve fiber, threshold for excitation increases
  • Impulse conduction slows
  • Rate of rise of action potential declines
  • Action potential amplitude decreases
  • Ability to generate an action potential is abolished
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11
Q

Local Anesthetics: Structure Activity Characteristics (5)

A
  • Smaller and more lipophilic molecules have faster rate of interaction with the Na channel receptor
  • Potency is also correlated with lipid solubility as long as the agent retains sufficient water solubility to diffuse to site of action
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12
Q

Water Soluble LAs (3)

A
  • Lidocaine
  • Procaine
  • Mepivacaine
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13
Q

More lipophilic LAs (3)

A
  • Tetracaine
  • Etidocaine
  • Bupivacaine

-More potent, longer DOA

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14
Q

Local Anesthetics: Action on Nerves (2)

A
  • May cause motor paralysis
  • A-delta and C fibers are small diameter fibers that participate in high frequency of pain transmission, they are blocked sooner with lower concentrations than A-alpha fibers
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15
Q

Local Anesthetic: Effect of Fiber Diameter (2)

A
  • Block small fibers better because the distance they can passively propagate is shorter (smaller fibers are first to fail to conduct)
  • Myelinated nerves must have 3 successive nodes blocked to halt propagation
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16
Q

Local Anesthetic: Effect of Firing Frequency (3)

A
  • More blockage at higher frequencies of depolarization and longer depolarizations
  • Sensory fibers (pain): high firing rate, long AP duration
  • Motor fibers: slower firing rate, shorter AP duration
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17
Q

Local Anesthetic: Effect of Fiber Position (3)

A
  • In large nerve trunks, motor nerves are usually located circumferentially, and are exposed first to drug when it is administered by injection into the tissue surrounding the nerve
  • Therefore, the motor nerve block can occur before the sensory block in large, mixed nerves
  • In extremities, proximal sensory fibers are on the outer layer (distal the core), so infiltration block of large nerve anesthesia is proximal first then distal
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18
Q

Local Anesthetic: Effects on Other Excitable Membranes (2)

A
  • Effects on cardiac cell membranes are of major clinical significance. May be useful as antiarrhythmic agents at concentrations lower than those required to produce nerve block, and all can cause arrhythmias in high enough concentration
  • LAs also have weak neuromuscular blocking effects but they are of little significance
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19
Q

Conditions that affect onset/duration of LA (5)

A
  • Vasoconstrictors
  • Intracellular acidosis: can hasten onset, resulting in intracellular accumulation
  • Tachyphylaxis: rapid loss of effectiveness after few doses, can be due to extracellular acidosis
  • Repeated injections can deplete the buffer and result in acidosis and no drug movement
  • Toxicity: if blood levels increase too much, many systems will be affected
20
Q

How do vasocontrictors affect LAs?

A
  • Epinephrine and phenylephrine slow removal from site
  • This slows systemic absorption
  • And decreases systemic toxicity
21
Q

Local Anesthetics: CNS (4)

A
  • Sleepiness, lightheadedness, auditory and visual disturbance, restlessness
  • High concentration: nystagmus and shivering, seizures, CNS depression, death
  • Use smallest dose required
  • If seizures, use Benzos
22
Q

Local Anesthetics: PNS (3)

A
  • High concentration: damage nerve tissue
  • Chloropropcaine: can cause sensory and motor deficits after accidental spinal anesthesia
  • Lidocaine: severe neurotoxicity when used for prolonged periods due to pooling of drug at vulnerable spots
23
Q

Local Anesthetics: CV (6)

A
  • Direct effecs on cardiac and smooth muscle membrane, indirect on autonomic nerves
  • Blocs heart’s Na channels and depresses abnormal pacemaker activity
  • Depress strength of contraction (except cocaine)
  • Cause hypotension and arteriorlar dilation
  • Most cardiotoxic: Bupivacaine and etidocaine
  • Less cardiotoxic: Ropivacaine
24
Q

Cocaine + CV (5)

A
  • Blocks NOR reuptake
  • Causes vasoconstriction and hypertension
  • May cause arrhythmias
  • Vasconstriction can lead to ischemia and ulceration of mucus membranes
  • Vasconstriction useful in topical applications
25
Q

Local Anesthetics: Blood (6)

A
  • Large doses (prilocaine): methemoglobinemia
  • Accumulation of 0-toluidine which converts hemoglobin to methemoglobin
  • Patient can become cyanotic (if levels get to 3-5 mg/dl)
  • Causes decompensation in patients with pulmonary/cardiac disease
  • METHYLENE BLUE IV to reconvert (also vitamin C)
26
Q

Local Anesthetics: Allergic Reactions (2)

A
  • Ester type are metabolized to PABA derivatives (PABA is responsible for allergic reactions)
  • Amides are not metabolized by PABA and reactions are rare
27
Q

Topical Anesthesia (3)

A
  • Nose, mouth, throat, ear, GU, skin
  • Common: cocaine, tetracaine, lidocaine
  • Can be absorbed into circulation from mucous membranes or denuded skin
28
Q

TAC (8)

A
  • Tetracaine/Adrenaline (EPI)/Cocaine
  • Topical for laceration repair
  • Onset: 10 min
  • Don’t use with TCA’s, MAOI’s, HTN, or cardiac disorders
  • Not for skin flaps, mucus membranes, digits, nose, pinna of ear, penis
  • T: ester, long DOA, most potent, less water soluble than lidocaine, procaine, mepivacaine
  • E: vasoconstrictor
  • C: ester, medium DOA
29
Q

EMLA (7)

A
  • Eutectic Mixture of Local Anesthetics
  • Lidocaine: amide, medium potency, medium DOA
  • Prilocaine: amide, less potent, medium DOA
  • Don’t use on mucus membranes, eyes or in those with G6PD
  • May cause skin blanching, erythemia, itching, rash
  • Onset: 1 hour
  • Duration: 1-2 hours
30
Q

ELAMAX (LMX) (6)

A
  • 4% lidocaine
  • Onset: 30-60 min
  • Don’t use on mucus membranes, eyes or in those with G6PD
  • May cause skin blanching, erythemia, itching, rash
  • Vasoconstriction: 1.5 hours
  • Vasodilation: 2-3 hours
31
Q

Iontophoresis (4)

A
  • Using electrical current to transfer drug
  • Delivery is proportional to total electrical charge
  • Peak: 10-20 min
  • Usually lidocaine
32
Q

Infiltration Anesthesia (4)

A
  • Injection directly into tissue (superficial or deep)
  • Provides satisfactory anesthesia without disruption of normal bodily functions
  • Duration increased with epinephrine
  • Use: Lidocaine, Procaine, Bupivacaine
33
Q

Nerve Block Anesthesia (2)

A
  • Injection into nerve plexuses and around individual peripheral nerves
  • Never intentionally into a nerve
34
Q

Onset of a nerve block is affected by 4 things

A
  1. Proximity of injection to nerve
  2. Concentration and volume of drug
  3. Degree of ionization of drug
  4. Time
35
Q

What drugs determine the duration of a nerve block?

A
  • Short: procaine
  • Intermediate: lidocaine, mepivacaine
  • Long: bupivacaine, ropivacaine, tetracaine
36
Q

Spinal Anesthesia (5)

A
  • Injection into CSF in lumbar space
  • Use: lidocaine, tetracaine and bupivacaine
  • For short: procaine
  • Permanent neurological injury is rare
  • Avoid in patients with progressive spinal diseases
37
Q

Epidural Anesthesia (2)

A
  • Primary site of action is spinal nerve roots

- Can use LA and opioids (morphine, fentanyl) for post-op and chronic pain

38
Q

Procaine (5)

A
  • Ester
  • Very short plasma T1/2 and DOA
  • More water soluble
  • Used for infiltration anesthesia
  • Used for nerve blocks (shortest acting)
  • Used for short spinal anesthesia
39
Q

Tetracaine (5)

A
  • Ester
  • Less water soluble (more potent, longer DOA)
  • Common topical anesthetic
  • Used for nerve blocks (long acting)
  • Used for spinal anesthesia
40
Q

Benzocaine (1)

A

-Ester

41
Q

Lidocaine (9)

A
  • Amide
  • More water soluble
  • First modern local anesthetic, most widely used
  • Severe neurotoxicity when used for prolonged periods due to pooling of drug
  • Common topical anesthetic
  • Used for Iontophoresis
  • Used for infiltration anesthesia
  • Used for nerve blocks (intermediate acting)
  • Used for spinal anesthesia
42
Q

Mepivacaine (4)

A
  • Amide
  • More water soluble
  • Intermediate acting agent for injection
  • Used for nerve blocks (intermediate acting)
43
Q

Bupivacaine (7)

A
  • Amide
  • Slowest rate of liver metabolism
  • Less water soluble (more potent, longer DOA)
  • More cardiotoxic than others
  • Used for infiltration anesthesia
  • Used for nerve blocks (long acting)
  • Used for spinal anesthesia
44
Q

Etidocaine (3)

A
  • Amide
  • Less water soluble (more potent, longer DOA)
  • More cardiotoxic than others
45
Q

Prilocaine (3)

A
  • Amide
  • Fastest rate of liver metabolism
  • Large doses (>10mg/kg) cause methemoglobinemia
46
Q

Ropivacaine (4)

A
  • Amide
  • S stereoisomer of bupivacaine (less affinity for cardiac Na channel)
  • Similar to bupivacaine (less intense motor block and less cardiotoxicity)
  • Used for nerve blocks (long acting)
47
Q

Chloroprocaine (4)

A
  • Ester
  • Very short plasma T1/2 and DOA
  • Can cause sensory and motor deficits after accidental spinal anesthesia
  • Chlorinated derivative of procaine

xPharm Exam 2 (8 decks)

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