Local Anaesthetics

Question 1

Classification

Answer 1

Clinical uses :

1. Surface anaesthetics - cocaine, lignocaine, tetracaine, benzocaine, butylinobenzoate.
2. Injectable-
   a. Short acting low potency - procaine, chlororocaine
   b. Intermediate acting with intermediate potency - Lignocaine, prilocaine.
   c. Long acting high potency- Tetracaine, bupivacaine, ropivacaine.

Structural

1. Esters -
2. Amides - lignocaine, mepivacaine, bupivacaine, prilocaine.

Question 2

MOA

Answer 2

Local anaesthetics > penetrate nerve membrane > enter axon > reionization of LA > LA gain access to its receptor in open state of channel > LA blocks voltage gated sodium channel from inside, binds more tightly to inactived state and prolongs it > prevent entry of sodium ions into neuron > prevent depolarisation of AP> no generation and conduction of impulses

Question 3

Factors affecting LA

Answer 3

1. pKa : higher the pKa, slower is the onset and vice versa.
2. Degree of plasma protein binding : Higher degree, higher onset of action
3. Rate of diffusion from site of administration: initial concentration of drug
4. Lipid solubility: Higher solubility, higher potency. Lignocaine > procaine
5. Presence of vasoconstrictor : prolongs duration of action

Question 4

Pharmacological actions

Answer 4

1. Nervous sytem:
   a. Peripheral nerves - Autonomic are blocked earlier than somatic.
   b. CNS - cause stimulation initially, then depression in higher doses.
2. CVS:
   a. Heart : decrease abnormal pacemaker, contractility, conductivity, excitability,HR, CO.
   Increases effective refractory period.
   i. At high conc, i.v administration can cause arrthymias.
   ii. Bupivacaine is more toxic than other LAs
   iii. Lignocaine decreases automaticity, useful in ventricular arrthymias.

Question 5

Therapeutic uses of
Lignocaine 2-10%
Tetracaine 2%
Benzocaine

Answer 5

Anaesthesia of mucuous membrane of eyes, nose, mouth, cornea, urinary and UR tract, fissures, ulcers.

Question 6

Therapeutic uses of
Lignocaine 0.5%-1%
Procaine
Bupivacaine

Answer 6

Abcess drainage
Excision of small swellings
Suturing cut wounds

Question 7

Nerve block anaesthesia

Answer 7

Surgery and neuralgias

Question 8

Therapeutic uses
Lignocaine 1.5-5%
Bupivacaine 0.25-0.5%

Answer 8

Surgery on lower limbs, lower abdomen, perineum, caesarean section

Question 9

Therapeutic uses of

Epidural anaesthesia

Answer 9

Obstetric analgesia

Question 10

Intravenous regional anaesthesia

Therapeutic uses

Answer 10

Upper limb and lower limb surgeries

Question 11

Therapeutic uses

Oxeyhathazine

Answer 11

Peptic ulcer