An antiviral drug; a protease inhibitor. Saquinavir (Fortovase) and saquinavir mesylate (Invirase) are aids (acquired immunodeficiency syndrome) in combination with other drugs to treat the infection caused by HIV (human immunodeficiency virus). Saquinavir and saquinavir mesylate cannot cure HIV or AIDS, but they can help keep HIV from reproducing itself. The drugs seems to slow the destruction of the immune system.