Local anesthetics provide a reversible block in the conduction of impulses in nerve fibers. All local anesthetic drugs c

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Local Anesthetics Provide A Reversible Block In The Conduction Of Impulses In Nerve Fibers All Local Anesthetic Drugs C 1 (142.57 KiB) Viewed 10 times

Local anesthetics provide a reversible block in the conduction of impulses in nerve fibers. All local anesthetic drugs contain a lipophilic group, an intermediate chain, and a hydrophilic group. The intermediate chain may be either an ester (as in procaine) or an amide (as in lidocaine). The activity and potency of any local anesthetic depends on several aspects, including its chemical structure, and the pKa of the substance. Local anesthetics are weak bases, so they are kept in an acid solution in which they form a water-soluble salt. The base is lipid-soluble and can penetrate various tissue barriers. The concentration of base or cation in the solution depends on the pKa of the local anesthetic. A decrease in the amount of base facilitates removal of the local anesthetics, resulting in a shorter duration of action. The duration of action of a local anesthetic is also affected by the local vasodilation which most of them produce. Finally, experiments have shown that a nerve which has been recently and repetitively stimulated is more sensitive to a local anesthetic than a resting nerve. CH, H C₂Hs C-CH₂-N-C₂H₂ CH₂ Lidocaine at pH=9.0 Figure 1 ➡ ব $ Based on the passage, which of the following statements is most likely true? A. B. C. D. The higher the pKa of the local anesthetic, the lower the concentration of base in the tissue. The lower the pKa of the local anesthetic, the higher the concentration of acid in the tissue. The higher the Ka of the local anesthetic, the lower the concentration of base in the tissue. The lower the Ka of the local anesthetic, the lower the concentration of acid in the tissue.