An experimental antiretroviral drug developed by Watertown, Mass.-based Panacos Pharmaceuticals lowered participants' HIV viral loads by as much as 90% in a Phase IIa trial, the company announced on Monday, the Boston Herald reports (Arends, Boston Herald, 8/23). The drug -- called PA-457 -- is the first in a new class of antiretrovirals called maturation inhibitors, which block formation of a protein that coats HIV, according to the company. Without the coating of the protein capsid, viral copies are released from the host cell but are unable to infect other cells (AP/Yahoo! Finance, 8/22). The drug targets strains of HIV that have become resistant to other antiretroviral drugs, according to Panacos. Participants in the 10-day clinical trial were assigned to take one of four different doses of the drug once daily. The HIV-positive volunteers who took the two highest doses -- 100 milligrams and 200 milligrams -- showed significant viral load reduction (Geller, Reuters, 8/22). In addition, genetic tests conducted on 21 of the 33 participants showed no evidence of resistance to the drug (AP/Yahoo! Finance, 8/22). Panacos said it hopes to launch Phase III trials of the drug -- which is made from the bark of the European plane tree -- by early 2007 and file for market approval by 2008 (Chase, Wall Street Journal, 8/22). PA-457 has been granted fast-track status by FDA (Boston Herald, 8/23).

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