The Pharmacokinetics of Local Anesthesia

The onset of action of a local anesthetic is determined by the pKa. weak bases at an acidic pH will be charged and at a basic pH will be uncharged. The higher the pKa of the individual drug, the more it will be charged at physiologic pH and the slower the onset of action. So for the purposes of test questions in general onset of action is related to the pKa but in reality there are other factors like the potency or concentration that you can use.