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Pharm 1 > Local Anesthetics > Flashcards

Local Anesthetics Flashcards

1
Q

What are local anesthetics (LA)?

A

Drugs that reversibly block conduction of electrical impulse along nerve fibers
- removal of drug is followed by spontaneous and complete return of nerve conduction, without evidence of structural damage to nerve fibers

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2
Q

What is the ability of LA to produce reversible blockade of impulses along pathways dependent on?

A
  • physiochemical properties of LA

- anatomy of nerves being blocked

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3
Q

What is the difference in myelinated vs unmyelinated nerves?

A
  • Unmyelinated: lacks fatty myelin sheath, charge can leak, impulse can slow down as it goes
  • myelinated: impulse can jump, no electrolyte leaking, IMPULSE SPEEDS UP
    • Na+ propagates action potential
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4
Q

How does an action potential work along axons?

A

Exactly the same way as a muscle cell action potential, with Na+ and Ca++ moving into the cell and K+ moving out, only the resting membrane is -70mv

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5
Q

What factors of nerve fibers influence sensitivity to LA?

A

Diameter and myelination
SIZE effects susceptibility more than myelination
- smaller= more susceptible than myelin

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6
Q

Do different types of fibers (myellin/demyelinated) send a different type of pain impulse?

A

Yes

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7
Q

In spinal nerves, sensitivity to LA is:

A

1st: autonomic nerve fibers
2nd: sensory nerve fibers
3rd: motor nerve fibers

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8
Q

LA mechanism of action?

A
  • reversibly block Na+ Chanel’s
  • receptors, located on inside of cell have a greater affinity for charged from of LA
    • BUT first must penetrate cell membrane, much easier in uncharged state
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9
Q

How does LA get into cell to work on the receptors?

A
  • LA is given as a weak base
  • when injected into the body will stay in same form (body is a weak base too) and diffuse into cell
  • once inside the neuron- acidic environment separates LA into ionized and unionized forms
    • cation (ionized form) binds with receptor on inside of neuron
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10
Q

All LA have a similar structure of an aromatic ring with an amine group at the very end? What splits LA into 2 groups?

A

The intermediate group:

  • can either be an ester linkage or an amide linkage
    • clinically important as it affects metabolism and allergy potential
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11
Q

Which LA are esters?

A

Procaine
Chloroprocaine
Tetracaine
Cocaine

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12
Q

Which LA are amides?

A 
* If you remove the “caine” their is an “i” in all Am”i”des**
Lidocaine
Prilociane 
Levobupivicaine
Mepivacaine
Bupivacaine
Ropivacaine
Etidocaine
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13
Q

The onset of action depends on:

A
  • lipid solubility* —> main determinant in amount of LA that is in non-ionized form
  • pka is the pH of LA where amount of ionized and non-ionized form of drug are equal
  • LA with pka closes to physiologic pH will have HIGHER CONCENTRATIONS of non-ionized form that can readily pass through nerve cell membrane
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14
Q

What is ion trapping and what is it caused by?

A

Loss of penetration into nerve

  • occurs when injecting into an acidic area (ischemia)
  • a weak base injected into an acidic environment converts to ionized form and cannot enter cell*
    • will not work to control pain
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15
Q

Duration of action:

A
  • correlates with lipid solubility
  • higher lipid solubility = longer duration —> less likely to be cleared by blood flow (stored in lipid depot)
  • higher lipid soluble are typically highly protein bound
    —> adding large chemical radicals to amide results in greater protein binding
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16
Q

Which LA have a duration of 200 + minutes?

A

Robivicane and bupivicine

- tetracaine duration is 200 minutes

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17
Q

Which LA have a duration of 30-60 or 30-90 minutes?

A

Lidocaine: 30-60 minutes
Prilocaine: 30-90 minutes

18
Q

Which LA have duration in the 40 minutes range?

A

Mepicacaine: 45-90 minutes
Procaine: 40 minutes
Chlorpromazine: 45 minutes

19
Q

How long until the onset of action in most LA?

A

5-15 minutes

20
Q

If you have a 1% solution of lidocaine, what does that mean?

A

1G/100mL

21
Q

How are LA distributed?

A

Unlike most meds, LA are meant to remain in area of injection/application

  • the HIGHER the CONCENTRATION of drug that REMAINS AT THE AREA of the nerve, the FASTER the ONSET OF ACTION
  • Systemic absorption = offset and termination of drug effect
22
Q

How do LA leave the area of injection?

A

If close to blood vessels —> swept away more quickly
Sits in fatty tissue longer
- does not get metabolized in place-needs to dissipate away to be metabolized

23
Q

What does systemic absorption depend on?

A
  • Blood flow
  • specific agent
    • highly lipid soluble
    • intrinsic vasodilation properties
24
Q

What does adding vasoconstrictors (epi) to the mix do?

A
  • decreases vascular absorption
  • increases nerve cell uptake
  • enhances quality of anesthesia
  • prolongs duration of action
  • limits toxic effects *
25
Q

Why do you add epi to LA?

A

All LA, except cocaine, relax vascular smooth muscle—> vasodilation—> systemic absorption

 - epi counters the vasodilation
 - cocaine is the only one that doesn’t dilate—> strong vasoconstrictor (alpha and beta adrenergic stimulator)
26
Q

Once LA is absorbed systemically, how is it distributed?

A

Initially to highly perfused organs-> brain, lungs, liver, kidneys, heart

 - slower distribution to moderately perfused organs
       - muscles and gut (muscles d/t large mass)
27
Q

How are LAs with ester linkages metabolized?

A

Mainly by pseudocholinESTERase

  • targets “Ester” linkage
  • ester hydrolysis is a rapid process
  • H2O soluble metabolites are excreted in the urine
  • pts with genetically abnormal pseudocholinesterase are at risk for toxic side effects (you won’t know until you give the med)
28
Q

What enters have metabolites that can cause allergic reactions?

A

Procaine and Benzocaine

Metabolized to PABA, which causes an allergic reaction

29
Q

How are amides metabolized?

A

By CYP 450- liver takes longer than breaking ester linkages

  • decreased liver function decreases metabolism—>increases toxicity
  • metabolism depends on renal clearance
30
Q

Which LAs create metabolites that convert to methemoglobin?

A

Prilocaine and benzocaine

31
Q

What does methemoglobin do to the body?

A

Produces a left shift

  • brownish gray cyanosis
  • tachypnea
  • met. Acidosis
  • Severs s/s: tissue hypoxia, HA, irritability, LOC *
32
Q

What is the treatment for methemaglobinemia?

A

Methylene blue: immediate reversal

33
Q

Is methemoglobinemia an issue in healthy patients?

A

No, becomes a problem with anemia or CHF- pts that can’t tolerate decrease in O2 carrying capacity

34
Q

What does adding opioids, NaHCO3,and epi to LA do?

A

added to increase safety, quality, intensity, duration, and rate of anesthesia

35
Q

Toxicity of LA occurs when:

A
  • accidental IV administration

- excessive dose

36
Q

What will you see in toxicity?

A

Cardiac and cerebral effects

  • famous lidocaine side effects with systemic absorption—> gibberish, tinnitus, confusion, seizures, metallic Tate
  • will see HR and BP increase then both will drop
  • high death rate if significant toxicity
    • combo of bradycardia, heart block, and low BP cause cardiac arrest
37
Q

What is the treatment for systemic LA toxicity?

A

Lipid infusion: binds lipophillic med

38
Q

If you need to give LA and you pt has had an allergic reaction in the past what do you do?

A

Find out which one and if it’s an amide or ester-> then use one from the other class

39
Q

What is EMLA?

A

Mix of lido and prilocaine
Dermal pain receptors, lipophillic
- about 1 hours to onset of analgesia

40
Q

Can topical anesthetic absorb systemically?

A

Yes: avoid high blood flow membranes

41
Q

What is topical cocaine used for?

A

ENT- excellent in nasal surgery—> Shrinks nasal mucosa

- produces vasoconstriction by blocking norepinephrine and epinephrine uptake int adrenergic nerve endings

42
Q

What can happen if epinephrine is injected into nasal mucosa prior to cocaine admin?

A

Toxic effect of epi may occur since cocaine blocks epi reuptake
—>life threatening arrhythmias

Pharm 1 (9 decks)

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