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17 Cards in this Set

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What were the problems with thte first synthetic LA?
- Long onset of action
- Ester group thus allergic response
- Short acting
What are benefits of Lidocaine?
- Amide group: hypoallergenic
- Fast acting
- Long lasting effects
Why is Lidocaine given with adrenaline?
It causes vasoldilation - adrenaline reverses these effects and localises the effects
What are the 3 structural requirements of LAs?
- Hydrophobic group
- Hydrophilic group
- Intermediate bond (ester/amide)
What is Pka?
PH at which concentration of [ionised] and [unionised] LA is the same
What receptors are the targets of LAs?
Na channels
Describe the hydrophobic pathway
Unionised form of the drug enters membrane of axon and 'side steps' into pore of receptor (whether open/closed/inactive)
Describe the hydrophilic pathway
Ionised form of drug enters when the channel is open (use dependent) and binds to inner pore
Are LAs more active in acidic or alkaline pH?
Alkaline
What is the physiological pH?
7.4
What is pH like at infected sites of tissue?
acidic
LAs with lower pKa values are..more/less ionised?
Less
LAs with low pKa...
Better absorbed in nerve tissue (less ionised) but may be difficult to interact with binding site in Na channel
LAs with high pKa...
More ionised thus takes longer to take effect but more effective at blocking Na channel
LAs with higher or lower pKa is more efficient at blocking Na channel?
Higher
Are motor neurons affected by LAs?
No - LAs take effect on small diameter afferent neurons
Reasons for choosing LA over GA?
- Less nausea felt
- Long lasting effects even after surgery
- May reduce blood loss