How is the onset of local anesthesia affected in a patient with an active infection?

Correct answer: A. Onset is slower and the anesthesia is less profound

• A. CORRECT. Inflamed tissue is ACIDIC (pH falls toward 5–6 from the normal 7.4). Local anesthetics are weak bases: at low pH the equilibrium shifts toward the ionised, charged form, and only the uncharged base can cross the nerve membrane. Less drug gets inside the axon, so onset is SLOWER and the block is LESS PROFOUND. Increased vascularity from inflammation also carries drug away faster, and inflammatory mediators sensitise the nociceptors themselves.
• B. A vasoconstrictor becomes MORE valuable in inflamed tissue, not less, because it counteracts the rapid washout.
• C. Duration is shortened, not prolonged, because of the increased vascular washout.
• D. Increased blood flow does not speed onset — it removes the drug from the site more quickly, shortening and weakening the effect.

Note: Practical responses: block proximal to the infected field rather than infiltrating into it, consider a regional block, use articaine buccal infiltration, or buffer the solution with sodium bicarbonate to raise the pH.