Protease inhibitors are a class of medication used to treat or prevent viral infections. They act by inhibiting specific viral enzymes that are essential to the viral life cycle by cleaving viral proteins. A medication is a licenced drug taken to cure or reduce symptoms of an illness or medical condition. ... A virus is a microscopic parasite that infects cells in biological organisms. ... An infection is the detrimental colonization of a host organism by a foreign species. ... Ribbon diagram of the catalytically perfect enzyme TIM. Factor D enzyme crystal prevents the immune system from inappropriately running out of control. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...

There are various viruses for which protease inhibitors have been developed (or are presently undergoing testing):

• HIV/AIDS: antiretroviral protease inhibitors (saquinavir, ritonavir, indinavir, nelfinavir etc.)
• Hepatitis C: experimental agents: BILN 2061, VX 950.

Given the specificity of the target of these drugs there is the risk, as in antibiotics, of the development of drug-resistant mutated viruses. To reduce this risk it is common to use together different drugs aimed at different targets. The human immunodeficiency virus, commonly called HIV, is a retrovirus that primarily infects vital components of the human immune system such as CD4+ T cells, macrophages and dendritic cells. ... The Red Ribbon is the global symbol for solidarity with HIV positive people and those living with AIDS. AIDS is an acronym for Acquired Immunodeficiency Syndrome or Acquired Immune Deficiency Syndrome and is defined as a collection of symptoms and infections resulting from the depletion of the immune system caused... Antiretroviral drugs are medications for the treatment of infection by the retrovirus HIV. Different antiretroviral drugs act at various stages of the HIV life cycle. ... Saquinavir (Fortovase®, Roche) is a protease inhibitor, used as a component of HIV therapy. ... Ritonavir is a drug from the protease inhibitor class used to treat AIDS. It is manufactured as Norvir® by Abbott Laboratories. ... Nelfinavir (Viracept®) is an antitretroviral drug used in the treatment of the human immunodeficiency virus (HIV). ... Hepatitis C is a form of hepatitis liver inflammation caused by a virus, the Hepatitis C virus (HCV). ... An antibiotic is a drug that kills or slows the growth of bacteria. ...

A brief history of the development of protease inhibitors by Hoffman La Roche, Abbott, and Merck: http://inventors.about.com/library/inventors/bl_protease_inhibitors.htm