The local anesthetics are commonly used for minor surgical procedures often in combination with vasoconstrictors such as epinephrine. Onset of action may be accelerated by the addition of sodium bicarbonate, which enhances intracellular access of these weakly basic compounds. Articaine has the fastest onset of action. Local anesthetics are also used in spinal anesthesia and to produce autonomic blockade in ischemic conditions. Slow epidural infusion at low concentrations has been used successfully for postoperative analgesia. Repeated epidural injection in anesthetic doses may lead to tachyphylaxis, however. Intravenous local anesthetics may be used for reducing pain in the perioperative period. Oral and parenteral forms of local anesthetics are sometimes used adjunctively in neuropathic pain states.