Local Anaesthetics

Question 1

Order the following local anaesthetics by pKa and give their pKa values:

Ropivacaine, Bupivacaine, Prilocaine, Lidocaine

Answer 1

Prilocaine 7.7
Lidocaine 7.9
Ropivacaine 8.1
Bupivacaine 8.1

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Question 2

What factors affect the following properties of a local anaesthetic:

Onset
Duration
Potency

Answer 2

Onset - Anion
Duration - Protein Binding
Potency - Lipid Solubility

ODP - APL

Question 3

What is the pKa of Bupivacaine and Ropivacaine?

Answer 3

8.1

Question 4

Order the following local anaesthetics by lipid solubility and give their lipid solubility values:

Ropivacaine, Bupivacaine, Prilocaine, Lidocaine

Answer 4

Prilocaine 50
Lidocaine 150
Ropivacaine 300
Bananas 1000

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Question 5

Order the following local anaesthetics by plasma protein binding and give their protein binding values:

Ropivacaine, Bupivacaine, Prilocaine, Lidocaine

Answer 5

Prilocaine 55%
Lidocaine 70%
Ropivacaine 94%
Bupivacaine 95%

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Question 6

Which local anaesthetics have protein binding values ~95%?

Answer 6

Ropivacaine - 94%
Bupivacaine - 95%

Question 7

What is the lipid solubility and protein binding of Prilocaine?

Answer 7

Lipid Solubility 55
Protein Binding 50%

Question 8

What are the maximum safe dosing levels for the following local anaesthetics?

Ropivacaine, Bupivacaine, Prilocaine, Lidocaine

Lidocaine + Adrenaline

Answer 8

Bupivacaine - 2mg/kg
Ropivacaine - 3mg/kg
Lidocaine - 3mg/kg
Prilocaine - 6mg/kg
Lidocaine + Adrenaline - 7mg/kg

Question 9

List local anaesthetics from the amide group and outline their intermediate chemical structure

Answer 9

Lidocaine
Prilocaine
Bupivacaine
Ropivacaine

H-N-C=O - bonds outlined
(-NH.CO-) - textbook notation

Question 10

Are local anaesthetics weak acids or weak bases?

Answer 10

Weak Bases

Question 11

List local anaesthetics from the ester group

Answer 11

Cocaine
Procaine

O=C-O - bonds outlined
(-CO.O-) - textbook notation

Question 12

How is the effect on vascular tone different between local anaesthetics?

Answer 12

Most local anaesthetics cause vasodilation at low doses and vasoconstriction at high doses

Cocaine causes ONLY vasoconstriction

Question 13

How are local anaesthetics metabolised?

Answer 13

Esters:
hydrolysed by plasma cholinesterases

(exception = cocaine by Hepatic hydrolysis)

Amides:
hepatic metabolism by amidases - slower than plasma hydrolysis