The document discusses several classes of anti-retroviral drugs used to treat HIV, including fusion inhibitors like enfuvirtide which bind to gp41 and prevent viral fusion, CCR5 receptor inhibitors like maraviroc which block the CCR5 co-receptor used by some HIV strains, and integrase inhibitors like raltegravir and elvitegravir which are given orally and active against HIV-1 and 2 with some cross resistance between the two. Integrase inhibitors can be used as part of initial triple drug regimens or as add-on drugs in optimized regimens for treatment-resistant cases.