What distinguishes the cationic form of local anesthetics?

The cationic form of local anesthetics is indeed the form that binds to receptor sites in sodium channels. Local anesthetics exist in two forms in solution: a cationic (positively charged) form and a unionized (neutral) form. The cationic form is more active pharmacologically because it specifically interacts with the receptors on the sodium channels within the nerve membrane.

When a local anesthetic is applied, it often requires the cationic form to effectively block nerve impulse transmission. This occurs because the binding of the cationic form to the receptor sites on the sodium channels prevents sodium from entering the neuron, which is critical in the generation and propagation of action potentials. Thus, the effectiveness of local anesthetics in inhibiting nerve conduction is directly related to the cationic form's ability to engage with these sodium channels.

While lipid solubility plays a role in the drug's ability to penetrate nerve membranes and other factors like diffusion through tissues and duration of action are influenced by different properties of the local anesthetic, the primary distinguishing characteristic of the cationic form is its binding capability to the receptors in sodium channels.