LA Flashcards
Name 3 examples of Ester-type LA
Procaine
Cocaine
Tetracaine
Benzocaine (surface use only, use as dry powder)
Name 3 examples of Amide-type LA
Lidocaine
Mepivacaine
Bupivacaine
Etidocaine
Prilocaine
Ropivacaine
Arrange the Ester LA according to their duration of action (from shortest to longest)
Procaine (Short)
Cocaine (Medium)
Tetracaine (Long)
Arrange the Amide LA according to their duration of action (at least 3, from shortest to longest)
Lidocaine (Medium)
Mepivacaine (Medium)
Bupivacaine (Long)
Name a LA that is more cardiotoxic
Bupivacaine
How are ester-type LA metabolized?
They are metabolized by non-specific esterases from the blood.
How are amide-type LA metabolized.
They are metabolized by metabolic enzymes (Cytochrome P450 / CYP450).
Explain the mechanism of action of LA
Stop axonal conduction by blocking sodium channels in the axonal membrane > prevent sodium ion entry > slow down or bring conduction to a halt.
LA acts on all nerves:
Size: ___ > ___
Myelination: ___ > ___
Size: Small > Big
Myelination: Myelinated > Non -myelinated
Explain the pH dependency of LA
LA molecules are weak bases (pKa 8-9), ionized at physiological pH > less effective when injected into acidic tissue
Alkaline pH > Increased LA activity (ionized molecules low)
Acidic pH > decreased LA activity (ionized molecules high)
The incidence of allergic reactions for Ester type LA : Amide type LA is Low : Very Low. Why is that so?
Ester type LA are hydrolysed to PABA derivatives which can cause allergic reactions in a small percentage of population.
What group of LA is better for a patient with liver impairment?
Ester LA (Procaine, Cocaine, Tetracaine)
What group of LA is better for a patient with PABA allergy?
Amide LA (Eg. Lidocaine)
When can systemic toxicity arise from LA administration?
Unintended large dose of LA if accidentally injected IV
OR
Excessive LA injected locally (symptoms may appear late as compared to IV)
