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Flashcards in Local anesthetics Deck (26):
1

Local Anesthesia

Loss of sensation in a limited area of the body

2

MOA of local anesthetics

administered in Non-ionic form --> diffuse into the cells --> become Ionized --> block Na channel from the inside

3

Loss of sensation (chronologically)

1. Pain
2. Cold/warmth
3. Touch
4. Pressure
5. Motor (could be affected)

**Effects faster n small fibers

4

What are the major uses of local anesthetics

• Minor & quick procedure
• Adjunct to anesthesia
• Adjunct to treatment of acute pain --ANALGESIA **
• adjuvant to sedation
• anesthesia of fish/amphibians

5

Intravenous block (local anesthetic)

Large volumes of diluted local anesthetics injected into an extremity **ISOLATED from remainder of the circulation by TOURNIQUET**

6

What parameters determine by the structure of local anesthetic?

1. Onset
2. Duration
3. Potency

7

What are the 3 general segments of the local anesthetic drugs?

Weak Base
1. Hydrophobic (lipophilic) domain
2. Intermediate ester OR Amide linkage
3. Hydrophilic (lipophobic) domain

8

What determines the pKa value of local anesthetic?

Lipophobic group
• Tertiary amine
• Determines the ONSET of ACTION!!

9

What does the lipophilc group determine of local anesthetic?

Binding to hydrophobic
• affects Duration (protein binding) & Potency!
• also ↑ toxicity

10

What determines the "fate"/metabolism of local anesthetic?

** Intermediate chain

• Aminoamines = liver metabolism

• Aminoesters = Hydrolyzed in plasma (less toxic)

11

Which local anesthetic have low potency, short duration?

Procaine**
chlorprocaine

12

Which local anesthetic have intermediate potency/duration

Lidocaine*
Mepivacaine**
prilocaine

13

Which local anesthetic have High potency, long duration

Tetracaine*
Bupivacaine*
Roprivacaine**

14

Why does damaged tissue diminish efficacy of local anesthetics?

bc environment becomes acidic --> becomes ionized before entering cells

15

What is important to know about administration of local anesthetic?

• Rapid & voluminous vascular absorption is NOT desired --> CNS / Cardiotoxic

• Vascular absorption ↓ by Epi (vasoconstrictor)
-- also delays healing

16

If accidentally injected in the blood, which will be distributed more widely? (amino amides OR amino esters?

Aminoamines

17

What are systemic toxic effects of local anesthetics?

CNS tox
• sedation to excitation (nausea)
• muscle twitch
• convulsions
••• POSSIBLE DEATH -- Respiratory & Cardiac arrest

Cadiovascular system
• bradycardia
• arrhythmia
• hypotension

Allergic rxn -- Esp AminoESTERS

18

Lidocaine

Injectable local anesthetic
• AminoAMIDE
• 4X more potent than procaine
• DOG/CATTLE
• Overdose --> ventricular fibrillation / cardiac arrest
--> death

19

Mepivacaine

Injectable local anesthetic
• AminoAMIDE
• longer duration than lidocaine
• HORSE -- less likely to cause tissue rxn

20

Bupivacaine

Injectable local anesthetic
• AminoAMIDE
• More potent than lidocaine
• LONGER duration

21

Ropivacaine

Injectable local anesthetic
• longer lasting
• HIGH affinity for pain fibers (< motor)
• Epidural for Horse surgery

22

Topical local anesthetics

AminoESTERS
1. Tetracaine -- eye, nose & throat
2. Proparacaine -- cornea

** NOT if corneal ulcers

23

What is used for lameness dx in horse?

Mepivacaine
• DO NOT use Epi

24

Epidural local anesthetic

• inject in space btwn dura mater & bone/ligamentous wall of spinal canal
• lose of SENSORY & MOTOR innervation

• LG animals -- general anesthesia more used
- Xylazine + local anesthetic

25

Risks assoc'd w/ Epidural use of local anesthetics?

1. Hypotension (Symp paralysis)
2. Motor Paralysis (hind limb)
3. Ventilation impairment (intercostal paralysis if too far front)

26

Examples of uses of local anesthetics in dogs

1. Punch biopsy
-- around lesion (2-3 mls of lidocaine)
2. Needle cor biopsy of LN
-- around lesion & under skin (overlying the LN)
3. Bone Marrow
-- in & around site where the marrow needle will be introduced (skin to bone)