A local anesthetic injected near an acute periapical abscess gives poor anesthesia. Which explanation is most appropriate?

  • Correct answer

    The acidic tissue increases the ionized fraction of the drug, so less crosses the nerve membrane

  • Bacterial enzymes inactivate the vasoconstrictor in the solution

  • Tissue esterases rapidly hydrolyse amide anesthetics in inflamed tissue

  • The acidic tissue converts the drug into its lipid-soluble base form, which stays in the tissue

This question is one of 15 in AFK practice: Biomedical sciences. Test yourself on all of them.

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Explanations

  • Only the uncharged base form diffuses through the nerve sheath and membrane; low pH in inflamed tissue shifts the equilibrium toward the charged form, so less drug reaches the sodium channels. Amide anesthetics such as lidocaine are metabolized in the liver, not by tissue esterases.

    Source: Malamed, Handbook of Local Anesthesia — oneguy

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