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DPPT Unit 3 > Local anesthetics > Flashcards

Local anesthetics Flashcards

1
Q

What are the three structural components of cocaine and its derivatives?

A

(1) Aromatic portion
(2) Ester linkage
(3) Charged portion

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2
Q

What are characteristics of the lipophylic portion of cocaine derivatives?

A

(1) Must be aromatic moiety
(2) Greater lipid solubility instills greater potency, longer duration of action, and greater toxicity
(3) Partitions drug into lipid, away from sites of metabolism
(4) Receptor sites have lipophylic nature

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3
Q

What are characteristics of the hydrophyllic portion of cocaine derivatives?

A

(1) Secondary or tertiary amines with pKa 8-9
(2) Active form is cation
(3) Only uncharged drug has access to site of action, so extracellular pH influences therapeutic effectiveness

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4
Q

What do local buffers do to local anesthetics?

A

Local buffers increase concentration of unionized form of drug, allowing it to enter the cell

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5
Q

What does repeated injection of local anesthetic result in?

A

(1) Depletion of local buffer

2) Tacchyphylaxis (diminishing effectiveness of drug

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6
Q

How does infection impact local anesthetic?

A

Infected areas tend to have lower pH, reducing concentration of unionized local anesthetic and reducing absorption

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7
Q

What are the characteristics of ester local anesthetics?

A

(1) Ester linkage hydrolyzed by plasma esterases (2) resulting in short plasma half life
(3) Breakdown products are p-aminobenzoic acid derivatives, which are (4) allergenic amides

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8
Q

What are the characteristics of amide local anesthetics?

A

(1) Duration of action is determined by liver N-dealkylation and hydrolysis of amide linkage
(2) Allergic reactions rare

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9
Q

What are the ester local anesthetics?

A

(1) Cocaine
(2) Procaine
(3) Tetracaine
(4) Benzocaine

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10
Q

What are the amide local anesthetics?

A

(1) Lidocaine
(2) Mepivacaine
(3) Bupivacaine
(4) Etidocaine
(5) Prilocaine
(6) Ropivacaine

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11
Q

Where do local anesthetics act?

A

α subunit of sodium channels

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12
Q

How do local anesthetics reach their target?

A

(1) Isoleucine prevents local anesthetic from accessing target from extracellular side of pore
(2) Local anesthetic binds tyrosine in S6 of domain 4 in intracellular half of pore, blocking the channel

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13
Q

What are consequences of Na channel block?

6

A

(1) Increased action potential threshold
(2) Reduced rate of action potential rise
(3) Decreased conduction velocity
(4) Decreased frequency of neuronal conduction and increased refractory period (reducing pain)
(5) Frequency- or use-dependent block
(6) Complete conduction block

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14
Q

What is use-dependent block of Na current?

A

Effect of local anesthetics:

At higher action potential frequencies, current generated decreases

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15
Q

What nerve properties increase sensitivity to block by local anesthetic?

A

(1) Small diameter
(2) Lack of myelination
(3) Low conduction velocity

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16
Q

What are some adverse effects of local anesthetic spreading to other tissues?
(5)

A

(1) Heart - arrhythmias, most serious being v-fib or pacemaker arrest
(2) Brain - restlessness, tremors, convulsions, respiratory failure, death, block of inhibitory pathways
(3) Suppression of autonomic nervous system
(4) Block of nAchR on skeletal muscle
(5) Decreased contractility of smooth muscle

17
Q

What factors determine absorption from local site?

4

A

(1) Presence of vasoconstrictor (usually epinephrine)
(2) Dosage and frequency of injection
(3) pKa and oil/water partition coefficient of drug
(4) Local pH

18
Q

What are the routes of administration of local anesthetic?

5

A

(1) Injection:
(a) Field block anesthesia
(b) Infiltration of peripheral nerve
(c) Intravenous regional anesthesia
(d) Spinal anesthesia

(2) Topical application

19
Q

What is field block anesthesia?

A

Subcutaneous injection for cutaneous anesthesia

20
Q

What is infiltration of peripheral nerve?

A

(1) Injection into a nerve
(2) Target nerves:
Brachial plexus, cervical plexus, sciatic/femoral nerves, ulnar nerve

21
Q

What are the risks of peripheral nerve block?

A

(1) Potential to puncture blood vessels, which lie close
(2) Pain
(3) Nerve damage

22
Q

How is intravenous regional anesthesia performed?

6

A

(1) Cannulate (place tube in) vein of extremity
(2) Place elastic bandage on extremity and exsanguinate
(3) Inflate proximal tourniquet above systolic pressure
(4) Remove bandage
(5) Inject local anesthetic without epinephrine into vein
(6) Use for

23
Q

Where can spinal block be administered?

4

A

(1) Spinal block in subarachnoid space of spinal canal
(2) Epi- or peridural block in epidural space
(3) Caudal block in epidural space of caudal canal
(4) Paravertebral block outside of dura

24
Q

When is spinal block used?

A

Surgery of lower abdomen, lower extremities, and peritoneum

25
Q

What is a post-operative effect of spinal block?

A

Post-operative postural headache after dural punction

26
Q

What are the features of topical anesthesia?

A

(1) Used on skin, nose, mouth, throat, tracheobronchial tree, esophagus, and genitourinary tract
(2) Superficial effect
(3) Rapid absorption and thus risk of serious toxicity

27
Q

What are the characteristics of topical anesthesia toxicity?

6

A

(1) Poor correlation between amount injected and plasma concentration
(2) Vasoconstrictor agent can lead to tissue anoxia and damage
(3) Respiration is maintained
(4) Benzodiazepines can be used to control convulsions
(5) Cross placenta and affect fetus
(6) Toxic to peripheral nerves

28
Q

Cocaine: potency, duration, other characteristics?

A

(1) Low potency
(2) Medium duration
(3) Affects upper respiratory tract, is a vasoconstrictor, can be toxic, has abuse potential

29
Q

Procaine: potency, duration, other characteristics?

A

(1) Low potency
(2) Short duration
(3) Low potency, short duration, and slow onset limits use but used in infiltration block

30
Q

Tetracaine: potency, duration, other characteristics?

A

(1) Very high potency
(2) Long duration
(3) Used in spinal block, topical anesthesia of eye, toxic due to slow metabolism

31
Q

How is benzocaine used?

A

Topically only

32
Q

Lidocaine: potency, duration, other characteristics?

A

(1) Medium potency
(2) Medium duration
(3) Most widely used local anesthetic, good for patients with sensitivity

33
Q

Bupivacaine: potency, duration, other characteristics?

A

(1) Very high potency
(2) Long duration
(3) Used during labor, more cardiotoxic than lidocaine

34
Q

Mepivacaine: potency, duration, other characteristics?

A

(1) Low potency
(2) Medium duration
(3) Similar to lidocaine, more toxic to neonates

35
Q

Etidocaine: potency, duration, other characteristics?

A

(1) Very high potency
(2) Long duration
(3) Preferential motor block, cardiotoxic

36
Q

Prilocaine: potency, duration, other characteristics?

A

(1) Low/medium potency
(2) Medium duration
(3) Causes methemoglobinemia

DPPT Unit 3 (15 decks)

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