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Block 7 week 2 > Local Anesthetics - Duan > Flashcards

Local Anesthetics - Duan Flashcards

1
Q

What are the characteristics of local anesthetics?

A
  1. applied locally
  2. produce loss of sensation to pain in a specific area of the body
  3. no loss of consciousness
  4. mechanism - block axonal conduction in nerves when applied in appropriate concentrations
  5. mechanism is reversible
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2
Q

Which local anesthetics are esters?

A
  1. cocaine
  2. procaine
  3. tetracaine
  4. benzocaine
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3
Q

Which local anesthetics are amides?

A
  1. lidocaine
  2. etidocaine
  3. bupivacaine
  4. levobupivacaine
  5. mepivacaine
  6. prilocaine
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4
Q

What group is common to all of the ester anesthetics?

A

They all have a lipophilic group.

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5
Q

How do the ester anesthetics differ in duration of action?

A
  1. cocaine - medium duration
  2. procaine (novocain) - short duration of action
  3. Tetracaine - long duration
  4. benzocaine - topical use only
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6
Q

Describe cocaine.

A
  1. an ester
  2. hydrolyzed very rapidly in blood
  3. a potent sympathomimetic and vasoconstrictor
  4. a potent CNS stimulant
  5. very addictive
  6. behavioral toxicity similar to paranoid schizophrenia
  7. fatalities from arrhythmias (V-fib), myocardial infarction or seizures
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7
Q

What enzyme is responsible for hydrolyzing cocaine in the blood?

A

Pseudocholinesterase.

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8
Q

What properties of cocaine make it addictive?

A
  1. causes euphoria
  2. causes CNS stimulation
  3. reduces fatigue
  4. perceived increase in mental ability
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9
Q

Describe Procaine.

A
  1. brand name = novocaine
  2. the first synthetic local anesthetic - a derivative of cocaine
  3. slow onset
  4. short duration
  5. less potent than cocaine
  6. higher potential to cause allergic reactions
  7. sympathomimetic - causes release of adrenaline
  8. increases heart rate and feelings of nervousness
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10
Q

Describe chloroprocaine.

A
  1. also called nesacaine
  2. slightly more potent than procaine
  3. shorter duration of action than procaine
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11
Q

Describe Tetracaine.

A
  1. also called Pontocaine
  2. 10X more potent than procaine
  3. slower onset and longer duration of action than procaine
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12
Q

Describe Benzocaine.

A
  1. also called americaine, ora-jel and solarcaine
  2. does not contain the terminal hydrophilic amine group so only slightly soluble in water
  3. slowly absorbed with prolonged duration
  4. only used topically
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13
Q

What structural groups are common to the amide anesthetics?

A

They all have a lipophilic group and an amine substituent group.

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14
Q

What are the duration of action of the amide anesthetics?

A
  1. lidocaine - medium duration
  2. mepivacaine - medium duration
  3. bipuvacaine - long duration
  4. etidocaine - long duration
  5. prilocaine - medium duration
  6. rapivacaine - long duration
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15
Q

Describe Lidocaine.

A
  1. brand name = Xylocaine
  2. an amine
  3. inactive drug is activated in liver by amidase
  4. little allergic reaction
  5. 2-3 X more potent than procaine
  6. rapid onset of action
  7. longer duration of action when combined with epinephrine - increases half life
  8. clinically versatile
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16
Q

Describe how Lidocaine is activated and inactivated in the liver.

A

The inactive form undergoes N-dealkylation via amidase to become monoethylglicexylidide or MEGX. MEGX undergoes hydrolysis to the inactive glycine xylidide by a liver cytochrome P450 when inactivated.

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17
Q

Name some clinical applications of Lidocaine.

A
  1. can be used topically
  2. used as a peripheral nerve block
  3. used in infiltration anesthesia
  4. used as spinal anesthesia
  5. used in epidural anesthesia
  6. used as an anti- arrhythmia agent
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18
Q

Describe Mepivacaine.

A
  1. also called carbocaine
  2. pharmacologically similar to lidocaine
  3. coadminister with epinephrine to prolong duration of action
  4. effective without a vasoconstrictor
  5. can be used in elderly patients and those with cardiovascular disease
  6. not useful in obstetrics because of prolonged metabolism in fetus and neonate - increases risk of toxicity
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19
Q

Describe Bupivacaine.

A
  1. also called Marcaine
  2. 10X more potent than procaine
  3. long duration of action - about 24 hours
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20
Q

Describe Ropivacaine.

A
  1. long duration of action like Bupivacaine

2. slightly less potent than Bupivacaine

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21
Q

What is the MOA of pain?

A
  1. free nerve endings are stimulated
  2. upon stimulation, sodium enters the neuron and causes depolarization of the nerve and initiation of an AP
  3. the AP is propagated down the nerve to the CNS where it is interpreted as pain
22
Q

Describe the MOA of local anesthetics.

A

Local anesthetics block the inward sodium current by blocking he voltage gated sodium channels in neuronal membranes that are responsible of signal propagation, the membrane of the postsynaptic neuron will not depolarize and will thus fail to transmit an AP.

23
Q

What is the concept of differential block?

A
  1. preferentially block small-diameter, unmyelinated nerve fibers first. These are c-fibers for pain and temp stimuli.
  2. large diameter myelinated nerve fibers appear to be less susceptible and require greater doses to achieve neural blockade.
  3. size is more important than myelination as a factor for anesthesia
24
Q

Describe the order of pain blockage in reference to nerve fibers.

A

Local anesthetics work on certain nerve fibers more preferentially than others.

Small, unmyelinated nerve fibers > small, myelinated autonomic fibers > large, myelinated autonomic fibers.

25
Q

What is the order of sensory loss with reference to anesthetics?

A

Pain is lost first, temperature second, touch third and pressure sensation is lost last.

26
Q

Describe the routes of administration of local anesthetics.

A
  1. regional - inject into area of nerved fibers to be blocked
  2. topical - put onto surface - extensively used on mucous membranes such as nasal mucosa, mouth, urethra and wound margins
  3. infiltration - injection under the skin. Often used with epinephrine which causes vascular constriction. For use when there is a need to localize drug action. Minimally effective concentration should be used to avoid toxicity.
27
Q

Where are anesthetics injected when used for spinal block?

A

Into the subarachnoid space.

28
Q

Where are anesthetics injected when used for an epidural?

A

Administered outside of subarachnoid space but diffuses into it.

29
Q

Where are anesthetics injected when used for a caudal block?

A

Epidural space.

30
Q

What is a paravertebral nerve block?

A

?

31
Q

Describe a spinal nerve block.

A
  1. injection into subarachnoid space
  2. spread of anesthetics can be controlled by increasing density of anesthetic solution with 10% solution of glucose and by tilting the patient
  3. used for upper abdominal surgeries
  4. problems - if autonomics are blocked then there is a loss of sympathetic tone and hypotension can result
32
Q

Describe a Caudal block.

A
  1. injected into the epidural space of sacral canal

2. used for perinea and rectal procedures

33
Q

Describe a Caudal block.

A
  1. injected into the epidural space of sacral canal

2. used for perinea and rectal procedures

34
Q

Describe an Epidural block.

A
  1. administered outside but diffuses into subarachnoid space

2. used in labor and delivery and cesarean section

35
Q

What are some factors that affect the reaction of local anesthetics?

A
  1. lipid solubility of the anesthetic
  2. pH
  3. blood flow
36
Q

Describe how lipid solubility affects reaction of local anesthetics.

A

The higher the lipid solubility of the anesthetic, the faster the nerve penetration, blockage of sodium channels and onset of action will be.

37
Q

Describe how pH influences reaction of local anesthetics.

A
  1. The uncharged or unionized form of a drug can cross nerve membranes and gain access to their site of action to block sodium channels
  2. log(cationic form/uncharged form)=pKa-pH
  3. all local anesthetics are weak bases with pKa of 8-9
  4. decreases in pH shifts equilibrium toward ionized form, delaying the penetration of the drug and thus its onset of action. Decreases in tissue pH can occur in infected tissues
38
Q

Describe how blood flow can affect the reaction of local anesthetics.

A

Vasoconstriction can be used to limit vasodilation activity of a local anesthetic. This causes delay of systemic absorption and keeps the anesthetic in place for a longer period and prolongs the action of the drug locally. Epinephrine can be sued to causes vasoconstriction.

39
Q

Name a factor that affects the metabolic degradation of a local anesthetic.

A

Degradation will vary depending on whether a compound has an ester or amide linkage.

40
Q

Describe the metabolic degradation of esters.

A

Esters are extensively and rapidly hydrolyzed in blood by plasma pseudocholinesterase and also by liver esterase’s. The product is paraaminobenzoic acid or PABA.

41
Q

Describe the metabolic degradation of amides.

A

Amides undergo N-dealkylation followed by hydrolysis in the liver via cytochrome P450.

42
Q

Describe the order of degradation of some amide anesthetics.

A

Some anesthetics are degrades more quickly than others. Prilocaine>etidocaine>lidocaine>mepivacaine>ropivacaine>bupivacaine>levobupivacaine.

43
Q

What factors should be taken into account when using amide anesthetics?

A

Amide anesthetics are metabolized in the liver by cytochrome P450’s. This enzyme system is affected by liver disease, reduced hepatic blood flow and are also used to metabolize other drugs also. All of these factors can affect the biotransformation of amides.

44
Q

What are the systemic pharmacological effects of local anesthetics on the CNS?

A
  1. moderate doses lead to CNS stimulation

2. very high doses lead to CNS depression

45
Q

What are the systemic pharmacological effects of local anesthetics on the cardiovascular system?

A
  1. direct depressant effect on myocardium
  2. reduces excitability
  3. lowers contractility
  4. prolongs the refractory period
  5. slows conduction
  6. vasodilation
  7. vasocontriction - cocaine only
46
Q

Do hypersensitivity reactions occur with local anesthetics?

A

Yes. they are most common with esters since they form PABA when metabolized. PABA is a known allergen

47
Q

How is toxicity caused when using local anesthetics?

A

Toxicity is usually caused by systemic absorption and high concentration of local anesthetics due to unintentional IV injection.

48
Q

What factors are taken into account when deciding on dose or concentration of local anesthetic used?

A
  1. age
  2. weight
  3. health of individual
  4. type of solution used
  5. presence of vasoconstrictor
  6. maximum dose for an individual is usually between 70mg and 500 mg
49
Q

What are the affects of cardiovascular toxicity?

A
  1. reduced excitability
  2. reduced contractility
  3. reduced conduction
  4. blood vessel relaxation (leads to hypotension) or constriction (constriction with cocaine only)
50
Q

What are the affects of neurotoxicity?

A
  1. light headedness
  2. irritation and agitation - shivering or twitching
  3. seizures
  4. numbness

Block 7 week 2 (5 decks)

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