EPI-743 is an orally absorbed small molecule that readily crosses into the central nervous system. It works by targeting an enzyme NADPH quinone oxidoreductase 1 (NQO1). Its mode of action is to synchronize energy generation in mitochondria with the need to counter cellular redox stress. EPI-743 has recently received orphan drug status from the U.S. Food and Drug Administration (FDA). The FDA has allowed an Expanded Access program to provide EPI-743 to seriously ill patients diagnosed with inherited respiratory chain diseases of the mitochondria.