Saquinavir hard-gel capsule 27 (Invirase) was the first PI approved by the FDA, in December 1995. A carboxamide derivative specifically designed to inhibit HIV proteinase and prevent post-translational formation of viral proteins, saquinavir is a potent inhibitor of HIV-1 and HIV-2 proteinases without prior metabolic activation. At 12 nM concentration, saquinavir has a 50% inhibition of normal HIV, and at 11 nM it has a 50% inhibition of ZDV-resistant HIV.