Which properties of the drug are the ionized form of local anesthetics is mainly responsible for?

Receptor binding-answer: d (katzung, pp 418, brunton, pp 371) local anesthetics are weak bases and in the in the body fluids they exist either as the uncharged base (nonionized form ) or as a cation (ionized form). since the non ionized form is lipid soluble, it is important for diffusion through the cell membrane, but the cationic form is thought to be the one that binds to the receptor site, which is located on the na+ channel near the inner surface of the membrane. a, b, c) all these properties are actually more related to the nonionized form of the drug. in fact tissue redistribution usually occurs in lipid rich tissues, the liver biotransforms mainly lipid soluble drugs, systemic toxicity mainly affects the cns and only the lipid soluble form of the drug can easily cross the blood brain barrier. e) the half life of a drugs is related to its volume of distribution and its clearance, which in turn depend on many factors, not only on the ionized form of the drug.