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Pharm Exam 2 > Tisdale: Local Anesthetics > Flashcards

Tisdale: Local Anesthetics Flashcards

1
Q

MECHANISM OF ACTION
Normal Voltage Gated Sodium Channel Function

Sodium channels associated with:

A

Sodium channels associated with excitable membranes

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2
Q

MECHANISM OF ACTION
Normal Voltage Gated Sodium Channel Function

Exists in 3 conformations:

A

Exists in 3 conformations:
o Between impulses the channel is closed (resting; Na cannot enter)
o After stimulation (membrane depolarization) the channel is open (activated; Na enters)
o Transition from an open to closed conformation (inactive; Na cannot enter)

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3
Q

MECHANISM OF ACTION
Normal Voltage Gated Sodium Channel Function

After these events:

A

After these events, the membrane repolarizes and the channel reverts back to closed form

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4
Q

Local Anesthetic Mechanism of Action
Basics

Block:
Blockage prevents:

A

Block voltage-dependent Na channels associated with excitable membranes by reducing the influx of Na ions

Blockage prevents depolarization of the membrane and blocks conduction of the action potential

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5
Q

Local Anesthetic Mechanism of Action
Mechanism

Uncharged drug must:

Only ______ is pharmacologically active:

A

Uncharged drug must cross the nerve membrane to enter the cytoplasm, where it is re-protonated

Only the charged LA is pharmacologically active

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6
Q

Local Anesthetic Mechanism of Action
Mechanism

Charged LA binds:
Overall result:

A

Charged LA binds the receptor when the Na channel is in the open state, and stabilizes the inactive state

Overall result is blockade of Na current; if current is blocked over a critical length of the nerve, propagation across the blocked area is not possible

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7
Q

Structure OF LOCAL ANESTHETICS
General Properties

All LAs must contain:
Aromatic ring connected by:
pKa of most LAs between:

A

All LAs must contain an aromatic ring (lipophilic; increases potency and duration of action)

Aromatic ring connected by an intermediate chain via an ESTER or AMIDE bond to an ionizable group (ie. tertiary amine; gives water solubility to LAs)

pKa of most LAs between 7.8-9.0

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8
Q

Structure OF LOCAL ANESTHETICS
General Properties

pKa vs physiological pH:

A

Those with a pKa closest to physiological pH will have a higher concentration of nonionized base that can pass through the nerve cell membrane (more rapid onset)

LAs with moderate hydrophobiticity are the most clinically effective

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9
Q

Ester Containing LAs

Inactivated in the bloodstream by:
Patients with genetic abnormality:
termination of action depends on:
Overall:

A

Inactivated in the bloodstream by pseudocholinesterase (plasma cholinesterase or butyrylcholinesterase)

Patients that have genetic abnormality in this enzyme at increase risk for toxic side effects (slower metabolism)

CSF last esterase enzymes and therefore termination of action depends on absorption into the blood stream

Overall, shorter duration of action than amide LAs

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10
Q

Amide Containing LAs

Metabolized by:
Rate of metabolism depends on:

A

Metabolized by microsomal P450 enzymes in the liver (N-dealkylation or hydroxylation)

Rate of metabolism depends on the drug, but overall is much SLOWER than ester hydrolysis

Lidocaine > Mepivacaine > Ropivacaine > Bupivacaine

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11
Q

Amide Containing LAs

Decreases in hepatic function effects: (3)

A

Decreases in hepatic function or liver blood flow will reduce the metabolic rate (predispose to toxicity)
o Cirrhosis
o Congestive heart failure
o Vasopressors

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12
Q

Amide Containing LAs

Comparison in rates:

A

Lidocaine > Mepivacaine > Ropivacaine > Bupivacaine

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13
Q

Administration

Topical:
Infiltration:
Field Block:

A

Topical: anesthesia of the mucous membranes of the nose, mouth, throat, esophagus and genitourinary tract by direct application

Infiltration: injection of LA directly into tissue without considering course of cutaneous nerves (most common)

Field Block: subQ injection to anesthetize a region distal to the injection

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14
Q

Administration

Nerve Block:

Central Nerve Block:
Spinal:
Epidural:

A

Nerve Block: injection of LA into or around individual peripheral nerves or nerve plexuses

Central Nerve Block:
o Spinal: injection into the CSF in the lumbar space
o Epidural: injected into epidural space

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15
Q

Duration of Action:

Do NOT use where?
Examples:

A

Duration of Action:
- Limited unless blood flow to the area is reduced- administer with a vasoconstrictor (ie. EPI)
o Decrease rate of absorption and localize LA
o Rate LA destroyed=rate LA absorbed

Do NOT use in anatomical regions with limited collateral circulation (irreversible hypoxic damage, necrosis, gangrene)
o Examples: fingers, nose, penis, toes

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16
Q

Nerve Blockade
Differential Functional Blockade

Smaller type B and C fibers:
firing rate:

A

Smaller type B and C fibers (mediate pain) and small myelinated Type A delta fibers (pain and temperature) are blocked first

These sensory fibers have a HIGH firing rate and a long action potential duration, resulting in a more rapid blockade

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17
Q

Nerve Blockade
Differential Functional Blockade

Larger myelinated Types (3):
firing rate:

A

Larger myelinated Type Aα, Aβ and Aγ fibers (postural, touch, pressure and motor information) are blocked later

The motor fibers have a SLOW firing rate and a short action action potential duration, resulting in a slower blockade

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18
Q

Nerve Blockade

General Order of Functional Deficits after LA Administration:

A

General Order of Functional Deficits after LA Administration: pain, temperature, touch, pressure, motor fnc.

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19
Q

Nerve Blockade

Factors Affecting Rate of Block: (3)

A

Fiber diameter: smaller diameter results in faster block

Firing frequency: higher firing frequency results in faster block

Location in nerve bundle: those in the periphery of the bundle are blocked faster (exposed first and at higher concentrations)

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20
Q

Undesired Effects

CNS: (6)

A

o Stimulation (due to depression of cortical inhibitory pathways)
o Restlessness
o Dizzy
o Tremors
o Confusion
o Respiratory depression (main threat to life)

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21
Q

Undesired Effects

CV: (2)

A

o Myocardial depression (decreased electrical excitability, conduction rate and FOC)
o Some degree of arteriolar vasodilation (all LAs except cocaine cause smooth muscle relaxation)

22
Q

Undesired Effects

Smooth Muscle: (2)

A

o Depress contractions in GI tract

o Relax vascular and bronchial smooth muscle

23
Q

Undesired Effects
Hypersensitivity: (2)
More likely with:

A

o Allergic dermatitis
o Asthma
o More likely with esters because they are derivatives of PABA (known allergen)

24
Q

Cocaine

General:
Duration/Onset:

A

General: first local anesthetic

Duration/Onset: medium onset and medium duration

25
Q

Cocaine

Effects: (2)

A

Effects:
o Local anesthetic and CNS stimulant properties
o Potent vascoconstrictor

26
Q

Cocaine

Toxicity: (2)
Clinical Use:

A

Toxicity:
o CNS toxicity related to both local anesthetic properties AND influence on re-uptake of catecholamines
o Impaired reuptake associated with adrenergic phenomena (HTN, increase HR, arrhythmia, and other serious cardiac effecs)

Clinical Use: anesthesia of mucous membranes

27
Q

Procaine (Novocaine)

General:
Onset:
Anesthesia in _____ minutes

A

General: first synthetic anesthetic

Onset: slow onset (pka=8.9; the higher the pKa, the lower the concentration in membrane permeable form)
o Anesthesia in 2-5 minutes

28
Q

Procaine (Novocaine)

Duration:
Metabolism:
Clinical Use:

A

Duration: short duration (low hydrophobicity and therefore rapidly dissociates from the Na channel)
o Drug is not retained in tissue (rapid removal from site via the circulation)

Metabolism: hydrolyzed to PABA (be aware of allergy and interaction with sulfa drugs)

Clinical Use: infiltration and dental procedures

29
Q

Benzocaine

Potency:
Onset:
Duration:

A

Potency: low

Onset: rapid (initial effects obtained in 1 minute)

Duration: short-acting (effects last about 15-20 minutes)

30
Q

Benzocaine

Unique Mechanism:
Forms:

A

Unique Mechanism: stabilizes the CLOSED form of the Na channel (small/fits into the pore in the closed state)

Forms: cream, aerosol, ointment

31
Q

Benzocaine

Clinical Use: (3)

A

Clinical Use:
o Topical pain reliever
o Anesthesia of mucous membranes
o Insertion of medical devices

32
Q

Tetracaine

Potency:
Duration:

A

Potency: high

Duration: long duration of action (high hydrophobicity due to butyl group)
o Prolonged interaction with the Na channel
o Increased time associated with tissue surrounding the nerve

33
Q

Tetracaine

Toxicity:
Clinical Use:

A

Toxicity: may result due to the fact that it is more slowly metabolized than other ester LAs (released gradually from tissue into blood)

Clinical Use: spinal and topical anesthesia

34
Q

ESTER-DERIVED LOCAL ANESTHETICS: (4)

A

Cocaine
Procaine
Benzocaine
Tetracaine

35
Q

AMIDE-CONTAINING LOCAL ANESTHETICS: (3)

A

Lidocaine
Bupivacaine
Ropivacaine

36
Q

Lidocaine

General:
Onset:

A

General: prototype amide linked drug and most widely used

Onset: rapid (lowest pKa of all the LAs we learn)

37
Q

Lidocaine

Potency:
Duration:
Forms:

A

Potency: moderate

Duration: medium-long duration (1-2 hours)
o	Moderate hydrophobicity
o	Metabolites (from metabolism in the liver) retain some anesthetic activity

Forms: ointment, jelly, patch, aerosol, solution

38
Q

Lidocaine

Clinical Use: (5)

A 
o	Infiltration
o	Nerve block
o	Epidural
o	Spinal anesthesia
o	Topical anesthesia
39
Q

Bupivacaine

Potency:
Duration:
Hydrophobic/philic?

A

Potency: good

Duration: prolonged anesthesia (up to 16 hours)
- Highly hydrophobic (butyl piperidine group attached to tertiary N)

40
Q

Bupivacaine

Selective block:
Toxicities:

A

Selective block: more sensory than motor block (if you give a dilute solution)

Toxicities: cardiotoxic properties

41
Q

Bupivacaine

Clinical Use: (4)

A

o Epidural*
o Infiltration
o Nerve block
o Spinal anesthesia

42
Q

Ropivacaine

General:
Positive Features: ( 4)

A

General: newest amide LA; very similar to bupivacaine

Positive Features:
o	Low cardiotoxicity
o	Less lipid soluble
o	Preferentially blocks sensory neurons
o	Produces vasoconstriction itself (do not need to add EPI)
43
Q

Ropivacaine

Clinical Use: (3)

A

o Epidural
o Infiltration
o Nerve block

44
Q

Benzocaine

Potency:
pKa:
Parenteral Uses:
Topical Uses:

A

Low

No amine group

None

Dermal
Laryngeal
Oral

45
Q

Cocaine

Potency:
pKa:
Parenteral Uses:
Topical Uses:

A

Low

8.7

None

Nose
Mouth/throat
Ear

46
Q

Procaine

Potency:
pKa:
Parenteral Uses:
Topical Uses:

A

Low

8.9

Infiltration
Nerve block
Spinal

None

47
Q

Tetracaine

Potency:
pKa:
Parenteral Uses:
Topical Uses:

A

High

8.2

Spinal

Larynx
Trachea
Esophagus

48
Q

Lidocaine

Potency:
pKa:
Parenteral Uses:
Topical Uses:

A

Intermediate

7.8

Epidural
Infiltration
Nerve block
Spinal

Dermal
Laryngeal
Oral

49
Q

Bupivacaine

Potency:
pKa:
Parenteral Uses:
Topical Uses:

A

High

8.1

Epidural
Infiltration
Nerve block
Spinal

None

50
Q

Ropivacaine

Potency:
pKa:
Parenteral Uses:
Topical Uses:

A

High

8.1

Epidural
Infiltration
Nerve block

None

Pharm Exam 2 (13 decks)

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