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Pharm 2 > Test 3: Local Anesthetics Basic Overview > Flashcards

Test 3: Local Anesthetics Basic Overview Flashcards

1
Q

All currently available local anesthetics consist of a ______ phenyl ring and a ____ or ______ amine. (Blue box!)

A

All currently available local anesthetics consist of a lipophilic phenyl (benzene) ring and a tertiary or quaternary amine.

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2
Q

Describe the chemical structure of a local anesthetic.

A

A benzene ring (Lipophilic) on one side is bonded to a tertiary/quaternary amine (Hydrophilic) on the other side.
-The bond between the benzene ring and the carbon (Amine) group determines whether the drug is an amide or an ester.

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3
Q

What are the 3 characteristic segments in the chemical structure of a local anesthetic?

A

1) Intermediate ester or amide carbon group
2) Unsaturated aromatic ring/Benzene ring
-Lipophilicity
3) An amine end (tertiary or quaternary)
-Hydrophilicity
-Able to ionize at physiologic pH

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4
Q

Which LA is an example of a Racemic Mixture?

A

Bupivicaine

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5
Q

Which LA is an example of a pure enantomer?

A

Levobupivicaine

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6
Q

Which type of LA is metabolized via hydrolysis by plasma/tissue cholinesterase?

A

Esters
-Occurs throughout the body
-Rapid
-Exception: Cocaine

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7
Q

How is Cocaine metabolized?

A

In the Liver

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8
Q

Which type of LA is metabolized in the Liver by the CYP450 system?

A

Amides
-Significant blood level may develop with rapid absorption because it has to have a transport mechanism to get to blood from Liver. Hangs out in blood until then. Rapid absorption of a lot of it will decrease the enzymes, and lead to higher levels.

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9
Q

Which type of LA is more likely to have allergic reactions?

A

Esters > Amides due to PABA.
-Allergy to one ester is allergy to all.

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10
Q

What is PABA?

A

para-aminobenzoic acid

The reason why Esters have allergy potential.

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11
Q

If you have an allergy to one amide, can you switch them to another amide?

A

Yes.

Can’t do this for esters though.

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12
Q

Which type of LA has a shorter duration of action?

A

Esters
-Shorter due to rapid metabolism
-Tetracaine is the longest acting ester

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13
Q

Why are amides longer acting?

A

-Longer acting because they are more lipophilic & protein bound
-Require transport to the liver for metabolism

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14
Q

What is the class, onset, and DOA of Chloroprocaine?

A

-Ester
-Fast
-30-60 min

Comes in a higher concentration, so faster onset.

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15
Q

What is the class, onset, and DOA of Lidocaine?

A

-Amide
-Fast
-90-120 min

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16
Q

What is the class, onset, and DOA of Bupivicaine?

A

-Amide
-Slow
-180-600 min

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17
Q

What is the class, onset, and DOA of Ropivicaine?

A

-Amide
-Slow
-180-600

18
Q

What is Pka?

A

The pH at which 50% of a drug is in the charged (or ionized) and water-soluble form, whereas the remaining half is uncharged (or nonionized) and lipid soluble.
-LAs are weak bases

19
Q

What happens to weak bases at a pH significantly less than its pKa?

A

They become mostly ionized.
-Therefore drugs that have a higher pKa (relative to pH 7.4) are ionized to a greater extent at body pH than those with a lower pKa.

20
Q

Decreased pKa = ____ time to onset of action.

A

Decreased pKa = decreased time to onset of action (faster onset).
-In general, the closer the pKa is to pH 7.4, the more rapid the onset.
-Exception: Chloroprocaine

Because their ionization is less, local anesthetics with lower pK a (7.6–7.8), such as lidocaine, mepivacaine, and prilocaine, tend to have a more rapid onset of action than drugs with a greater pK a (8.1–8.6), such as bupivacaine, tetracaine, and procaine.

21
Q

Why does Chloroprocaine have a rapid onset of action?

A

-pKa is 9.1
But, using 3% concentration gives a rapid onset of action.

22
Q

A base in an alkaline environment is ______, ____ soluble, and _____ diffusable across the bilipid membrane. (Blue Box!)

A

A base in an alkaline environment is non-ionized, lipid soluble and easily diffusable across the bilipid membrane.

23
Q

Why are Local Anesthetics stored as acidic solutions?

A

-Longer shelf life.
-When we put them into body, now dropping it in a more basic environment, driving it towards the non-ionized form.

Manufacturers acidify local anesthetic solutions to increase solubility and stability (the free base is more susceptible to photodegradation and aldehyde formation), which results in a longer shelf life.

24
Q

Local anesthetics provide _____, as long as they are in the site of deposition. (Blue box!)

A

Local anesthetics provide analgesia, as long as they are in the site of deposition.

25
Q

LAs are primarily what kind of amines?

A

Tertiary - can cross BBB.

26
Q

What is the target site of action for a LA?

A

The Voltage gated Na Channel
-Binding site is inside the cell (pore channel). Binds to ionized form
-Channel has to be open or inactive for binding to occur.

27
Q

What are factors that potency is dependent on?

A

-pH and pKa
-Potency is related to lipid solubility.

28
Q

How does onset differ between SAB and epidurals?

A

-SAB: no nerve sheaths, direct access to nerves, fast onset
-Epidural: requires 10xs more dose to produce dense block

29
Q

How does protein binding affect DOA of LAs?

A

Increased Protein binding = Increased DOA

30
Q

How does vascular uptake effect the DOA of LAs?

A

-LA provide analgesia as long as they are in the site of deposition
-Vasoconstriction slows the rate of uptake (keeping it at site of action).
-Lido + Epi (or neosynephrine)
-Not really necessary with long acting LA’s b/c the DOA of the Bupiv can outlast that of Epi.

31
Q

Describe what happens when a Local Anesthetic is injected into the tissues.

A

1) Inject a weak base LA into the tissues. (tissues are typically a more acidic environment)
2) Protonates depending on pH & pKa (some becomes ionized form)
3) Non-ionized form crosses the lipid membrane
4) Intracellular pH is decreased and the LA equilibrates again (becomes ionized once inside the cell)
5) Ionized LA antagonizes the Voltage Gated Na+ Channel (attaches to the binding site)

32
Q

___ layers of connective tissue are barriers to local anesthetics. (Blue Box!)

A

3 layers of connective tissue are barriers to local anesthetics.
-Endoneurium
-Perineurium
-Epineurium

33
Q

What is an axon?

A

An extension of a centrally located neuron.
-Functional unit of peripheral nerves

34
Q

What is the axolemma?

A

Cell membrane like structure.
-Bilipid Layer
-Proteins and ion channels
-Axoplasm – intracellular contents

35
Q

What are Schwann Cells?

A

Cells that support and insulate each neuron
-Small non-myelinated nerves, Schwann cells cover several axons
-Larger myelinated nerves, Schwann cells cover only one axon and produce several concentric layers of myelin.

36
Q

What is the myelin sheath?

A

-Allows for faster conduction of impulses
-Myelinated nerves are larger & more difficult to block than unmyelinated nerves

37
Q

What are the Nodes of Ranvier?

A

Segments of nerve between Schwann cells that do not contain myelin.
-Contain the Voltage Gated Sodium Channels - LA site of action
-Saltatory Conduction – AP’s jump from node to node
-Have to act on 3 nodes to block conduction.

38
Q

What are fascicles?

A

A bundle of axons in a peripheral nerve.

39
Q

What is the Endoneurium?

A

Delicate connective tissue composed of longitudinally arranged collagen around the myelin sheath of each myelinated nerve fiber
-Surrounds and embeds the axons in the fasiculi.

40
Q

What is the Perineurium?

A

-Layers of flattened overlapping collagenous cells
-Binds a group of axons together to form a fascicle

41
Q

What is the Epineurium?

A

Areolar connective tissue that functionally holds the fasciles together to form the peripheral nerves.

Pharm 2 (40 decks)

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