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Pain and Anxiety > LA Pharmacology > Flashcards

LA Pharmacology Flashcards

1
Q

What are local anesthetics produced as

A

2% solutions (20X1.8 = 236mg/carpule)
3% solutions (54mg/carpule)
4% solutions (72mg/carpule)
0.5% solutions (9mg/carpule)

Each carpule = 1.8 ml

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2
Q

What are carpule contents

A

LA drug
Sodium hydroxide/sodium chloride = buffering agent
Vasoconstrictor (EPI or Levonordefrin)
Vasoconstrictor preservative (sodium bisulfite = increased allergic rxns) - will decrease solution pH = more acidic = delayed onset

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3
Q

What was in LA solutions prior to 1984

A

Without EPI added METHYLPARABEN as preservative (many allergic rxns, if pt had allergic rxn before 1984 consider allergy to parabens)

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4
Q

What are the 2 groups of LA

A

Esters and amides

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5
Q

What are the ester local anesthetics?

A

Increased allergic reactions- 10% (if allergic to one ester probably allergic to all)

  • metabolized in BLOOD plasma via pseudocholinesterase
  • (small amt metab in liver)

Includes topicals only: benzocaine, tetracaine, procaine

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6
Q

What are the amide local anesthetics

A

ALL INJECTABLE LA in US are amides, topicals can be amides too
- low cross-hypersensitivity with esters
- metabolized in Liver

Lipocaine, mepivacaine, bupivacaine (metabolized in liver only = increased toxicity in liver disease)
Prilocaine (metabolized by liver+lung, shorter half life from lungs)
Articaine (metabolized by plasma 90% and liver 10%) - shortest half life

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7
Q

What is the chemical structure of LA

A

Lipophillic Aromatic Ring
-Base = inactive form
-Penetrates membrane (cannot bind receptors unless it picks up H+ ion)

Intermediate Linkage
-Determines if L.A. is ester/amide

Hydrophilic Terminal Amine
-Dissociates becoming tertiary amine → enters nerve → gains H+ ion = ionized = binds to receptor sites = active form
-Must pick up H+ inside the cell. Then becomes ionized again = active and can bind to receptor sites

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8
Q

What is the action of local anesthetics

A

Cation = active form, binds to receptor but cannot cross membrane
Anion = cannot bind but this is the one that can penetrate membrane

Loses H+ to cross membrane, then picks it up again to bind

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9
Q

What is pharmacodynamics

A

Physiological effects of drug on body

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10
Q

What are the pharmodynamics of LA

A
  • LA include cations and anions
  • All LA are acidic before injection (more cations)
  • all LA are vasodialators
  • the pKa of LA predicts the proportion of acid:base molecules
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11
Q

What are the cations

A

Acid - RNH+

Active form of drug that cannot cross membrane but can bind receptor

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12
Q

What are the anions

A

Base - RN

Lipid soluble form that crosses membrane (inactive, cannot bind membrane, picks back up H+ to bind)

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13
Q

All LA are ______ before injection

A

Acidic solutions

More cations than anions in cartridge

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14
Q

LA are vaso——?

A

Vasodialators

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15
Q

Decreased pKa =

A

Increased anions = increased base (RN molecules) = fast diffusion across membrane = rapid onset

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16
Q

Increased pKa =

A

Increased cations = decreased base = slow diffusion access membrane = slower onset

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17
Q

What is the effect of infections on LA?

A

Infected tissues are acidic (pH = 5-6)
LA is acidic, when injected into acidic tissues less molecules can cross the membrane = inadequate anesthesia

RNH+ molecules cannot dissociate H+ ions in acidic tissue = active form cannot enter cell membrane

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18
Q

What is the effect of nerve size on LA

A

LA must penetrate 8-10mm of myelinated nerve length (3-4 nodes of Ranvier) to block a nerve impulse

Increased volume of LA required for large nerves (like in IAN)

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19
Q

Increased concentration =

A

Increased diffusion through membrane = RAPID onset

20
Q

Increased lipid solubility =

A

Increased potency = decreased dose needed, (enhances diffusion of drug through nerve)

21
Q

Increased protein binding of molecules =

A

Increased duration (bind more strongly to receptor, prolonging anesthetic presence at site of action)

22
Q

Increased vasodilation of LA =

A

Decreased potency + decreased duration = increased dose needed

(Vasodilation = increase blood flow and increased removal of LA molecules from site)

23
Q

What is pharmacokinetics and what does it include?

A

Action of drug within the body

Includes: onset of action, induction, recovery from block, reinvention, duration/potency, distribution, biotransformation/metabolism, excretion, systemic effects

24
Q

What is onset of action and what is the primary factor

A

Period from LA deposit to blocked impulse conduction

pKa of LA is primary factor (decrease pKa = rapid onset) - pKa determines amount of ionized molecules in solution

Site is a secondary factor (small diameter nerves = rapid onset)

25
Q

What is induction of LA and what is the primary factor

A

Diffusion of molecules across membrane

Initial concentration of LA is primary factor
(Increased conc = increased diffusion = rapid onset)

*anesthetic loses concentration from tissue fluid, capillaries, lymphatics, anatomical barriers (bone)

26
Q

What is recovery from LA block and what is the primary factor

A

Reversal of LA action

Degree of binding to receptor site is primary factor (different for each LA = chemical characteristic)

Slower process than induction

27
Q

The degree of protein binding at the receptor site controls:

A

Duration of anesthetic action
Speed of nerve recovery from local anesthesia

28
Q

What happens with reinjection of LA in fully/partially recovered pt?

A

Partially recovered nerve fibers (pt still numb) = small volume is effective with rapid onset

Fully recovered nerve fibers (no numbness) = tachyphylaxis occurs = tolerance to LA = LA is ineffective

29
Q

What is duration of LA and what are the 3 factors

A

duration of LA = potency

  1. Protein binding of specific LA (stronger = increased duration = increased potency)
  2. Vascularity of injection site (increased = decreased duration = decreased potency)
  3. Vasoconstrictor in LA (increased = decreased blood flow = increased duration = increased potency)
30
Q

What is the distribution of LA and what organs have high concentrations

A

After absorption —> LA are distributed throughout body

Highly vascular organs have increased concentrations = brain (crosses barrier), heart, lungs, liver, kidneys

31
Q

What is toxicity directly related to?

A

Amount of LA accumulated in tissues

32
Q

Increased absorption =

A

Increased risk of systemic toxicity

33
Q

Total dose administered increased =

A

Increased absorption
(All molecules diffuse out of Na+ channels into bloodstream)

34
Q

Increased LA concentration =

A

Increased absorption

35
Q

What route of administration increased absorption?

A

Topical

36
Q

What site of injection increased absorption

A

Intravascular

37
Q

Increased vasoconstriction =

A

Decreased absorption

38
Q

What are the things that affect absorption of LA

A

Total dose administered
LA concentration
Route of administration
Vascularity of administration site
Presence of vasoconstrictor

39
Q

What is the biotransformation of LA

A

Metabolism of the drug

Measured in half-life (time for 50% to be removed)

40
Q

Increased half life =

A

Increased risk for systemic toxicity

41
Q

What LA has the shortest half life

A

Articaine

42
Q

Where are LA excreted

A

Kidneys - primary excretory organ for all LA

Small amt of ester LA are excreted unchanged in urine, still small but greater percentage of amide LA are excreted unchanged in urine

Increased risk of systemic toxicity in severe renal disease due to build up of drug when not cleared by kidneys

43
Q

Increased blood levels =

A

Increased toxicity

44
Q

What are the systemic effects of LA

A

Affect CNS and CV system after absorbed into blood (before metabolized)

45
Q

Toxicity and adverse reactions are directly related to….

A

1) Nature of specific LA (vasodilation)
2) Concentration of drug
3) Route of administration –>
intravascular = increased absorption
topical = increased absorption
4) Dose administered
5) Rate of injection –> increased rate = increased absorption
6) Vascularity of site
7) Age of patient –> children/elderly = decreased rate of metabolism
8) Weight of patients (decreased dose for decreased weight)
9) Health of patient = decreased metabolism associated with diseases/meds

Pain and Anxiety (12 decks)

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