Lidocaine, also known as xylocaine and lignocaine, is a medication used to numb tissue in a specific area and to treat ventricular tachycardia. It can also be used for nerve blocks. Lidocaine mixed with a small amount of epinephrine is available to allow larger doses to be used as numbing and to make it last longer. When used as an injectable it typically begins working within four minutes and lasts for half an hour to three hours. Lidocaine may also be applied directly to the skin for numbing. Common side effects with intravenous use include sleepiness, muscle twitching, confusion, changes in vision, numbness, tingling, and vomiting. It can cause low blood pressure and an irregular heart rate. There are concerns that injecting it into a joint can cause problems with the cartilage. It appears to be generally safe for use in pregnancy. A lower dose may be required in those with liver problems. It is generally safe to use in those allergic to tetracaine or benzocaine. Lidocaine is an antiarrhythmic medication of the class Ib type. Lidocaine works by blocking sodium channels and thus decreasing the rate of contractions of the heart. When used locally as a numbing agent, local neurons cannot signal the brain. Lidocaine was discovered in 1946 and went on sale in 1948. It is on the WHO Model List of Essential Medicines, the most important medications needed in a basic healthcare system. It is available as a generic medication and is not very expensive. The wholesale cost in the developing world in 2014 was US$0.45 to $1.05 wholesale per 20ml vial of medication.