Why are local anesthetics not effective in inflamed tissues?

Local anesthetics are less effective in inflamed tissues primarily due to the lower pH present in these environments. In inflamed tissues, the pH tends to drop because of the accumulation of lactic acid and other metabolic byproducts resulting from the inflammatory process. This acidic environment affects the ionization of local anesthetics, which are weak bases.

Local anesthetics typically exist in two forms: ionized (charged) and non-ionized (uncharged). The non-ionized form is crucial for effectively penetrating nerve membranes to exert their anesthetic effect. However, when the pH decreases—as it does in inflamed tissues—there is an increase in the ionized fraction of the drug. The ionized form cannot effectively cross cell membranes, which significantly hampers the local anesthetic's ability to block nerve conduction.

Therefore, the heightened ionization due to the lower pH in inflamed tissues is the reason why local anesthetics show reduced efficacy in those contexts, making option B the correct choice.