INBDE (Integrated National Board Dental Examination) Practice Exam

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How does pKa affect local anesthetics?

Reduces effectiveness
Impacts duration
Onset of action
Increases toxicity

The correct answer is: Onset of action

The correct answer is C. pKa affects the onset of action of local anesthetics. The pKa is the pH at which 50% of the drug is in its ionized form and 50% is in its non-ionized form. Local anesthetics in their non-ionized form can cross cell membranes more easily to reach their target site within nerve fibers. Therefore, a lower pKa results in a higher proportion of non-ionized drug molecules and a faster onset of action. Options A, B, and D are incorrect because pKa primarily affects the onset of action and not the overall effectiveness, duration, or toxicity of local anesthetics.