Local anesthetic "resistance".

The incidence of inadequate analgesia despite technically well performed injections led our clinic to prospectively test patients for response to a variety of local aesthetics. Skin testing was performed on the skin of the forearm away from the site of pathology. Patients were asked to identify "which is the most numb" of the skin wheals. Although most were equally numb to all three local anesthetics (lidocaine, bupivicaine, and mepivicaine), 7.5% of the patients consistently chose mepivicaine as the local anesthetic resulting in the most hypoesthesia. For patients who had previously undergone an unsuccessful procedure with bupivicaine (the standard local anesthetic used in our practice), the same procedure with mepivicaine provided good relief. Patients are now questioned on their initial evaluation about a history of difficulty getting numb, for instance at the dentist, and preemptively skin tested prior to any invasive procedure.