INBDE (Integrated National Board Dental Examination) Practice Exam

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Which local anesthetic has the highest pKa?

Lidocaine
Articaine
Bupivacaine
Mepivacaine

The correct answer is: Bupivacaine

Bupivacaine has the highest pKa among the options listed (pKa of around 8.1-9.2), which means it has the lowest percentage of the uncharged (lipid-soluble) form at physiological pH compared to the other local anesthetics mentioned. This characteristic can result in a slower onset of action but a longer duration of action due to slower penetration into nerve fibers. Lidocaine, articaine, and mepivacaine have lower pKa values compared to bupivacaine, leading to a higher percentage of the lipid-soluble form at physiological pH, allowing for quicker onset of action but shorter duration compared to bupivacaine.