Prezista is the manufacturers name for the generic drug darunavir, and is made by a company called Jannsen pharmaceuticals of Titusville New Jersey. Prezista is a protease inhibitor, and antiviral medication given to people to help control (HIV) human immunodeficiency virus. The way prezista does its job is to reduce the amount of (HIV) in the body, which in turn will help improve the immune system, and lessen the chances for the patient to contract an (HIV) infection. A doctor will prescribe this treatment in combination with Norvir, generic name ritonavir. The exact dosage depends on different factors such as has the patient been treated with any other (HIV) medications prior.