pharmacology .. local anesthesia
TRANSCRIPT
P H R M A C O L O G Y - NOTE 8 - Local Anesthesia
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LOCAL ANESHESIA
weak Potency & short Duration
Procaine Chloroprocaine
moderate Potency & intermediate Duration
Lidocaine (Xylocaine)
Mepivacaine
Prilocaine
high Potency & long Duration
Tetracaine
Bupivacaine
Etidocaine
Ropivacaine
LA
Esters
Amide
•produce local loss of sensation without loss of consciousness
•Procaine
•Chloroprocaine
•Tetracaine
•Benzocaine
•Benoxinate
•Lidocaine (Xylocaine)
•Mepivacaine
•Bupivacaine
•Etidocaine
P H R M A C O L O G Y - NOTE 8 - Local Anesthesia
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DRUG PHARMACOKINETIC ACTION USES SIDE EFFECT
Wea
k P
ote
ncy
&
sho
rt d
ura
tio
n
Procaine Administration
Local injection.
Local application ( solution, powder or cream)
Absorption
NOT desirable because: It duration. It systemic side effects.
Metabolism
Easter, fastly metabolized by tissues & plasma esterase.
Into PABA (cause allergy). Short duration.
Amides, slowly metabolized by liver microsomal enzymes.
Longer duration. .
Mechanism of action
LA block nerve conduction (initiation & propagation of AP) by: Binding to Na
+ channels &
prevent Na+ permeability.
Action
LA are lipid soluble / weak base.
At pH= 7.4, o they are UNIONIZED molecule. o They pass lipid membrane.
When reach the cytoplasm, o They become (ionized +
unionized). o The IONIZED molecules:
Bind to Na+
channels. Block Na
+ influx.
Prevent AP.
The action are susceptible for (small diameter / unmylinated) fibers more than (large diameter / mylinated) fibers.
1) Surface anesthesia: o on Skin (wound & ulcer) o on MM (mouth or nose). o in Ophthalmology (corneal A). o powder, solution creams or ointment
are used. 2) Infiltration anesthesia.
o as in (wound suturing, cyst removal). 3) Individual nerve block anesthesia.
o as in Dental anesthesia. 4) Spinal Epidural anesthesia.
o as in surgery of (LL, abd, pelvis, rectum).
5) Treatment of cardiac dysrhythmia.
Usually minimum, because:
o Applied locally. o Combinewd with
vasoconstrictors. 1) Hypotension. 2) Bradicardia. 3) CNS:
Tinnitus. Lightheadness. Headache. Convulsion.
4) Allergy (in ester type).
Side effects occur due to: o High dose. o Injected into BV.
They are potent & have long duration.
Chloroprocaine
Mo
der
ate
Po
ten
cy
& In
term
edia
te
du
rati
on
Lidocaine (Xylocaine)
Mepivacaine
Prilocaine
Hig
h P
oten
cy &
lo
ng d
ura
tion
Tetracaine 1) Infiltration anesthesia. o as in (wound suturing, cyst removal).
2) Individual nerve block anesthesia. o as in Dental anesthesia.
3) Spinal Epidural anesthesia. o as in surgery of (LL, abd, pelvis,
rectum). 4) Treatment of cardiac dysrhythmia.
Bupivacaine
Etidocaine
Ropivacaine
Benoxinate It is ester LA. In ophthalmology for corneal A because : NO mydriasis. NO corneal injury.
Benzocaine Used as powder or cream.
Because it is insoluble, it produces less systemic toxicity.
Surface anesthesia on Skin (wound & ulcer)
INFLUENCING FACTORS
IF Advantage Disadvantage
1 Dosage High Fast onset / long duration side effect
2 Site BV side effect / Short duration
3 Lipid solubility LS effect
4 Infection/ inflammation
pH action / ionized /effect
Vaso-dilation
absorb / side effect/ duration
5 Type of solution Alkali Less painful / fast onset / non-ionized / action / effect
6 + vasoconstrictors duration/ absorb /side effect