Which local anesthetic has the lowest ratio of dose needed to produce cardiovascular collapse relative to dose causing CNS toxicity?

Which local anesthetic has the lowest ratio of dose needed to produce cardiovascular collapse relative to dose causing CNS toxicity?

• A. Lidocaine
• B. Etidocaine
• C. Bupivacaine
• D. Prilocaine

Answer: (C)

This question tests the relationship between CNS toxicity and cardiovascular toxicity for different local anesthetics. The sweetest spot here is the drug that has the smallest safety margin between the brain effects and the heart effects—that is, the dose that triggers cardiovascular collapse is not far above the dose that causes CNS toxicity. Bupivacaine stands out because of its high potency and deep, long-lasting block of cardiac sodium channels. Its high lipid solubility means it readily penetrates cardiac tissue and binds Na channels with high affinity, causing marked depression of conduction and risk of arrhythmias. This makes cardiovascular collapse occur at doses only modestly higher than those producing CNS symptoms, giving the smallest CNS-to-CV toxicity ratio among the options. The other agents—lidocaine, prilocaine, and etidocaine—have comparatively larger safety margins between CNS effects and cardiovascular collapse, so their ratios are higher. This is why bupivacaine is known for greater cardiotoxic potential relative to CNS toxicity.

This question tests the relationship between CNS toxicity and cardiovascular toxicity for different local anesthetics. The sweetest spot here is the drug that has the smallest safety margin between the brain effects and the heart effects—that is, the dose that triggers cardiovascular collapse is not far above the dose that causes CNS toxicity.

Bupivacaine stands out because of its high potency and deep, long-lasting block of cardiac sodium channels. Its high lipid solubility means it readily penetrates cardiac tissue and binds Na channels with high affinity, causing marked depression of conduction and risk of arrhythmias. This makes cardiovascular collapse occur at doses only modestly higher than those producing CNS symptoms, giving the smallest CNS-to-CV toxicity ratio among the options.

The other agents—lidocaine, prilocaine, and etidocaine—have comparatively larger safety margins between CNS effects and cardiovascular collapse, so their ratios are higher. This is why bupivacaine is known for greater cardiotoxic potential relative to CNS toxicity.