20 Questions
What is the primary mechanism of action of local anaesthetics?
Inhibiting the influx of sodium (Na+) ions through voltage-gated Na+ channels
What is a major concern with the use of cocaine as a local anaesthetic?
Its addictive and psychogenic effects
What determines the effectiveness of local anaesthetics?
Lipid solubility and local pH
Why are local anaesthetics injected locally or applied topically?
To avoid unwanted systemic effects
What is the primary reason for using additives in local anaesthetics?
To improve their onset and duration of action
What is the primary mechanism by which vasoconstrictors in local anaesthetics prolong the duration of action?
Reduced blood flow, leading to slower removal of the local anaesthetic
What is the effect of vasoconstrictors on the onset of anaesthesia?
Faster onset
Which of the following is a disadvantage of using vasoconstrictors in local anaesthetics?
Alterations in cardiovascular response
What is the order of blockade of nerve fibres when a local anaesthetic is deposited in proximity to a peripheral nerve?
Outer mantle to inner core
What is the primary mechanism of action of local anaesthetics on nerve fibres?
Blockade of nerve fibre by diffusion along a concentration gradient
What is the primary reason why local anesthetics are less effective in inflamed tissue?
The increased number of H+ ions in the tissue reduces the concentration of the lipid-soluble base form of the local anesthetic
What is the significance of the pKa value of a local anesthetic?
It determines the percentage of the drug that is ionized at a given pH
Why do local anesthetics with higher lipid solubility have a greater potency and duration of action?
Because they have a greater proximity to their sites of action due to their greater affinity for lipid membranes
What is the consequence of a higher pKa value of a local anesthetic?
A slower onset of action, but a more prolonged duration of action
What is the downside of local anesthetics with higher lipid solubility?
They have a higher toxicity, decreasing the therapeutic index
What is the primary mechanism of metabolism of lidocaine in the plasma?
Hydrolysis
Which of the following local anaesthetics is most likely to cause methaemoglobinemia?
Prilocaine
What is the primary reason for the cardiotoxicity of bupivacaine?
Its slow metabolism by the liver
What is the primary site of action of local anaesthetics on nociceptors?
Voltage-gated sodium channel
What is the percentage of unchanged local anaesthetics excreted through the renal system?
3-5%
Learn how local anesthetics work to block nerve impulses and pain transmission. Understand the mechanism of action of lipid-soluble bases and their interaction with Na+ channels. Test your knowledge with this quiz!
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