ABSTRACT
Local anesthetics are acidic, in the pH range of 5-7 . Their pH further decreases with the addition of epinephrine to the anesthetic solution. Once they enter the tissue, the body’s bicarbonate buffer system converts the acidic solution to a more basic form. This is the active, uncharged form of the drug that can diffuse through the plasma membrane of the neurons. Bupivicaine, with its higher pKa, has a slower onset of action than lidocaine, which has a lower pKa. Acidic tissue, such as a hy poxic or infected wound, increases the fraction of ionized drug, thus delaying the onset and decreasing the efficacy of local anesthetics.
