Local anaesthesia drugs

Question 1

Give 2 examples of Amides

Answer 1

1. lignocaine

2. bupivicaine

Question 2

Describe local/regional anaesthetics pharmacologically?

Answer 2

• weak bases
• the more lipid soluble(lipophillic) the more potent but the onset of action is much slower
• the longer the intermediate part the longer the duration of the drug

Question 3

What 2 groups are local anaesthetics broken up into?

Answer 3

1. Amides

2. Esthers

Question 4

What drug falls under esters?

Answer 4

Cocaine and procaine

Question 5

Give some characteristics of esters?

Answer 5

• Still used by dentists and ENT specialists
• more heat labile
• easily broken down
• cannot e stored for a long time
• less stable in solution
• allergic reaction because of PABA(Para-aminobenzoate)

Question 6

What is special about lignocaine?

Answer 6

It can be used as an anti-arrythmic drug

Question 7

What is the mechanism of action of local anaesthetic drugs?

Answer 7

In order for an action potential to occur then Na has to go through the sodium potassium pump
Lignocaine/bupivicaine prevents that by becoming unionised and blocking the sodium potassium pump and not allowing the action potential to occur and thus no pain is felt

Question 8

What is the effect of the local anaesthetic?

Answer 8

1. Stops nerve conduction which is the goal
2. vasodilation of vascular smooth muscle
3. lignocaine has an anti-arrythmic function
4. Central nervous system excitability( confusion, agitation, coma, convulsions and depression) if toxic levels are reached

Question 9

How many more times is bupivicaine more potent than lignocaine?

Answer 9

4 times

Question 10

What is pKA?

Answer 10

It is the pH of the drug when 50% is ionised and 50% is non-ionised
The lower the pKa(closer to the body’s pKa the faster the onset of action of the drug)

Question 11

What is the pKa of lignocaine and bupivicaine?

And what does it mean?

Answer 11

lignocaine- 7,9
bupivicaine- 8,1
Lignocaine has a faster onset of action

Question 12

Which nerves are the first to experience the drug?

Answer 12

The smallest nerves are first(these being the temperature or sensory nerves)
The bigger nerves such as motor nerves are the last to fallout and so the patient is still able to move

Question 13

What is the dosage of lignocaine?

And what is the dosage when we add adrenaline and why?

Answer 13

1. Dosage is 3mg/kg

2. Dosage with adrenaline is 7mg/kg because the adrenaline causes vasoconstriction

Question 14

What is the dosage of bupivicaine?

Answer 14

1. 2mg/kg and it does not change with the addition of adrenaline

Question 15

How are Esters metabolised?

Answer 15

1. Through tissue or blood esterases which is preferred however it means that there is the PABA allergic reaction

Question 16

How are Amides metabolised?

Answer 16

Through the liver

Cytochrome P450

Question 17

What is the half life of lignocaine?

Answer 17

90 minutes

Question 18

What is the dosage of lignocaine when used as an anti-arrythmic drug?

Answer 18

1-1,5 mg/kg IV with a maximum dose of 3mg/kg