In inflamed/infected tissue (periapical abscess), local anesthetics are LESS effective because:

Correct answer: D. The acidic environment shifts the anesthetic toward its ionized form, which cannot penetrate the nerve membrane

• A. While vasodilation does increase systemic uptake, this is not the primary mechanism of LA failure in infection.
• B. If the pKa were LOWER than tissue pH, more non-ionized form would be available; the problem is the opposite — the acidic tissue pH shifts the balance toward ionized form.
• C. Local anesthetic molecules are not chemically destroyed by inflammation.
• D. Correct. Local anesthetics must be in their non-ionized (free base) form to penetrate the lipid nerve membrane. Inflamed tissue has a lower pH (more acidic) due to bacterial metabolism and inflammatory byproducts. In an acidic environment, the equilibrium shifts toward the ionized (cationic) form of the anesthetic, which CANNOT cross the membrane — resulting in failed anesthesia.