Local Anesthetics

Question 1

Compare local anesthetic esters & amides

Answer 1

Esters, broken down by pseudocholine esterases: shorter duration of action, liable to allergy (PABA derivatives), duration of action is prolonged in genetic enzyme deficiency
Amides, longer duration of action, liable to induce systemic toxicity, duration of action prolonged in liver disease & reduced hepatic blood flow

Question 2

Mechanism of action of LA

Answer 2

Bind to receptors on inner surface of Na channel in nerve membranes resulting in their blockade —>inhibition of generation & propagation of action poetntials

Question 3

Mention factors affecting sensitivity of nerves to LA

Answer 3

1. Rate of firing (more in sensory)
2. Nerve size (more in small nerves)

Question 4

pKa of LA is…..

Answer 4

7.7 to 9 (weak bases)

Question 5

Mention factors affecting activity of local anesthetics

Answer 5

1. Plasma protein binding affects duration of action
2. Lipid solubility affects potency
3. PKa of drug affects speed of onset
4. Extracellular pH (infections/repeated injections of lidocaine HCl, dec activity. Adding NaCO3 to LA, inc activity)
5. Addition of vasoconstrictors prolongs duration of action

Question 6

……is preferred as VC in cardiac patients

Answer 6

Felypressin

Question 7

……has more rapid onset, while…..has longer duration of action & more potent

Answer 7

Lidocaine
Bupivacaine

Question 8

Mention adverse effects of LA

Answer 8

CNS: low conc: sleepiness, restlessness, numbness, metalic taste, high conc: tremors, convulsions, respiratory depression, coma & death
Neurotoxicity: due to direct local effect of high conc
CVS: Hypotension & bradycardia
Allergy: with esters (PABA derivatives)
Side effects of VC aadded to LA

Question 9

Describe drug interactions of LA

Answer 9

Lidocaine and propranolol: reduces hepatic blood flow and impairs clearance leading to toxicity
Lidocaine with adrenaline + propranolol: severe rise in BP
Lidocaine with adrenaline + TCA: hypertensive crisis
Procaine + sulphonamides, dec effect of sulphonamides

Question 10

Deug of surface anesthesia

Answer 10

Lidocaine

Question 11

Denstistry uses….technique

Answer 11

Nerve block

Question 12

Mention uses of spinal anesthesia

Answer 12

Used for surgery of abdomen, pelvis & legs when general anesthesia is CI

Question 13

Mention side effects of spinal anesthesia

Answer 13

Headache (due to CSF leakage & traction on sensitive structures), hypotension (sympathetic nerve block), spinal root injury & infection.

Question 14

Epidural anesthsia is used for…..

Answer 14

Obstertics for painless labour