Natdac® is an inhibitor of the viral (hepatitis C virus) protein NS5A, which is used in the replication of hepatitis C virus within the liver cells (hepatocytes) and, thus, prevents the virus from entering infected hepatocytes into the blood. Thanks to this action, it is possible to prevent the spread of the virus in the body. Natdac® (da?latasvir) is a highly specific direct action agent against hepatitis C virus (HCV) and has no pronounced activity against other RNA and DNA containing viruses, including human immunodeficiency virus (HIV). Natdac®, as an inhibitor of the nonstructural protein 5A (NS5A), a multifunctional protein required for HCV replication, suppresses two stages of the life cycle of the virus-viral RNA replication and virion assembly.