A cluster of new anti-AIDS drugs are expected to be approved for general use later this year, giving hope to patients who have developed drug-resistant forms of the virus. This is because the new agents hit different parts of the virus compared with existing anti-HIV drugs, which means that there should be very little initial drug-resistance. The new agents include two "fusion inhibitors", maraviroc, made by Pfizer, and vicrivoroc, which has been developed by Schering Plough. These drugs block the ability of HIV to lock onto a molecule on the cell surface called CCR5, which the virus needs in order to penetrate and infect. The other agent, raltegravir, is made by Merck. It locks onto a viral protein called integrase and prevents it from inserting a copy of its genetic material into the host DNA, which is a critical step in the viral lifecycle. When both of these approaches have been combined (a fusion inhibitor given together with the integrase inhibitor), in patients with drug-resistant disease, the viral load in the bloodstream fell to undetectable levels, indicating good disease control.