Kaplan says: Local anesthetics bind preferentially to activated Na channels.
First aid says: Local anesthetics bind preferentially to INactivated Na channels.
So who's right? Once again, both are correct! According to Katzung Basic and Clinical Pharmacology (LANGE), local anesthetics have an increased affinity for BOTH activated and inactivated states of Na channels, but they have a low affinity for resting Na channels. Remember that Na channels in the heart and neurons have 3 states according to their M and h gates (resting, activated, and inactivated). Neurons with higher rates of firing have more Na channels in the activated and inactivated states, and less in the resting/ready state.