local anesthetic, a medication used to prevent the transmission of impulses through nerves to eliminate sensation in a defined area of the body. It can also prevent motor and autonomic function in this area. The effect is transient (time limited). Drugs available for local anesthesia are classified as members of the ester or the amide family. Specific preparations are available for topical administration, infiltration, and various kinds of regional administration, including field block, regional block, epidural block, and spinal block. People who are sensitive to local anesthetics of one group often can tolerate those of the other group. The vascularity of the injection site, the speed with which the drug is given, the rapidity of action of the drug, and the presence of epinephrine or Neo-Cobefrin in the solution may affect any adverse response.