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AIDS drug holds promise as smallpox pill

By Rhonda Rowland
CNN Medical Unit

SAN DIEGO, California (CNN) -- Research suggests that an antiviral drug used to treat AIDS-related infections could be developed into a pill to treat people exposed to smallpox in a biological weapons attack.

A highly potent form of the drug cidofovir, developed by researchers at the University of California at San Diego and tested by the U.S. Army Medical Research Institute, proved effective in treating mice infected with cowpox and in laboratory tests on the smallpox virus itself.

Researchers believe this more potent form of the drug could be harnessed into a pill that could be used to treat people exposed to smallpox, which was eradicated globally in the 1980s but could be a possible agent in a biological weapon.

"We thought it could work orally, but what was surprising was the activity against smallpox and viruses in the pox family was 100 times more potent than [intravenous] cidofovir itself," said Dr. Karl Hostetler of UCSD.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Disease, which funded the research, said while the results are "promising," the new form of cidofovir is just one agent being studied to fight smallpox.

"The good news is this is highly effective in blocking smallpox in the laboratory and in a mouse model," Fauci said. "But the sobering news is it's only been studied in the test tube and mouse model, so we shouldn't get too excited yet. Smallpox is an important disease that we need therapies for, so that's why we're looking at this with great interest."

Cidofovir, in its current form, is used to treat infections commonly seen in patients with HIV and AIDS, but it can cause serious kidney damage. However, higher potency generally means fewer side effects, so the pill form could be less toxic.

While the smallpox vaccine is still considered the best way to treat smallpox exposure because it remains effective even if given several days afterward, Hostetler said the pill could be an alternative.

"In its intravenous form, it would be difficult to widely use [cidofovir], " said Hostetler. "But in a pill form, if you think of an army in a region where there could be a release of smallpox, they could carry it and, on instruction, take the necessary oral doses."

Hostetler said the doctors who developed a vaccine strategy to fight smallpox did not have knowledge of antiviral drugs.

"Since then, we've learned from treating AIDS, hepatitis and herpes that it's possible to control viral diseases with drugs," he said.

However, Hostetler said researchers are at least a year away from testing the new form of the drug in humans to determine if it is safe. Even if it is never needed to fight smallpox, the pill could be useful against other viruses, such as Epstein-Barr and the herpes family, he said.

"Hopefully, we can develop it not just for a disease we hope to not see again but other diseases out there where better treatments are still needed," he said.

Once the drug was developed by Hostetler's team in San Diego, Army researchers tested it on the smallpox virus strains stored at the Centers for Disease Control and Prevention in Atlanta, one of two known stockpiles of the virus. The other is held by Russia.

The research findings are being presented at the 15th International Conference on Antiviral Research in Prague, Czech Republic.


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