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The newspaper of The Johns Hopkins University March 12, 2007 | Vol. 36 No. 25
 
Widely used hepatitis B drug spurs HIV drug resistance

JHU experts notify FDA, caution co-infected patients about entecavir

By David March
Johns Hopkins Medicine

A Johns Hopkins study has proved false an established medical practice that an antiretroviral drug widely used to treat hepatitis B liver infections was safe to use on its own in patients co-infected with HIV. Their findings demonstrate that treatment with entecavir leads to cross-resistance to other antiviral drugs used to treat the AIDS virus.

"Our results show that entecavir is no different from any other that has been shown to be active against HIV; it breeds resistance rapidly, despite its ability to reduce the amount of HIV in the body," said senior study author and infectious disease specialist Chloe Thio.

Researchers say the findings, presented Feb. 28 at the 2007 Conference on Retroviruses and Opportunistic Infections in Los Angeles, have serious implications for the more than 4 million people worldwide believed to be infected with both viral illnesses but who need to treat their hepatitis B and are not yet on anti-HIV drugs.

Authors of the study have informed the U.S. Food and Drug Administration of their results so that prescribing physicians can be notified and drug labeling changed. They also have notified Bristol-Myers Squibb, which makes and sells entecavir under the brand name Baraclude.

"The alert should go out to co-infected people to consult with their physicians immediately about entecavir to see if it is the right drug to treat their hepatitis B in the first place and to evaluate alternative therapies," said Thio, an associate professor of medicine at the Johns Hopkins School of Medicine.

Thio said she has stopped prescribing entecavir as her first option in treating hepatitis B in co-infected patients who are not already using drugs to suppress HIV.

"The good news is that co-infected patients already on HIV therapy can still use entecavir to treat their hepatitis B, but the bad news is that there are now fewer options for treating hepatitis B first," she said. Hepatitis B infection attacks the liver and can lead to cirrhosis, liver cancer or even death from liver failure.

Entecavir, first marketed in March 2005, has been a leading treatment for chronic forms of hepatitis B, which can be fatal to almost a quarter of those infected if it is left untreated. The drug's label information currently states that it has no clinical effects on HIV.

According to Thio, some co-infected patients decide to treat their hepatitis B infection first if HIV has not yet weakened their immune system and to avoid the debilitating side effects of anti-HIV medications.

In the Johns Hopkins study, researchers found in both laboratory and clinical tests that within six months of entecavir therapy, a so-called M184V mutation of HIV develops. Thio said viruses with this mutation are known to be resistant to lamivudine, better known as 3TC, a medication that prevents HIV replication and "is a cornerstone of most drug-combination therapies used to fight the immune system disease." Because lamivudine is in the same category of HIV therapies as another widely used drug, emtricitabine, its effectiveness is also compromised by entecavir, she said.

Thio began to investigate entecavir's effects on HIV in fall 2006 after noticing reports of anti-HIV activity in two co-infected patients, one at the Johns Hopkins Moore Clinic, which specializes in HIV/AIDS care, and another at a San Diego medical center. The patients (and there is now a third case) were taking only entecavir yet showed a tenfold decrease in the amount of HIV in their blood.

Previous studies had shown entecavir not to have any significant effects on HIV, but those studies were based on older tests that could not quantify the effects of HIV on individual immune cells or detect mutations. Thio said she believed that the recent patient cases called for a more thorough investigation with more advanced techniques.

She and her team combined various concentrations of entecavir with 100,000 human immune cells from a healthy blood donor, then infected them with an HIV test virus and measured the number of cells infected over time.

The lab test, developed at Johns Hopkins by study co-author Robert Siliciano, a professor at Johns Hopkins and a Howard Hughes Medical Institute investigator, specifically tests what drugs affect HIV and can be tailored to probe effects on any particular mutant of HIV.

Lab results showed that entecavir, in concentrations less than a 10th of what is used in humans, cut the number of newly infected cells in half; however, at increasing concentrations, the drug had no greater impact on suppressing HIV replication. HIV is a virus renowned for its ability to change form and thus evade or develop resistance to therapies designed to stop its action.

Similar testing with entecavir, immune cells and the M184V form of HIV showed that the drug did not stop the virus from infecting the cells. This provided evidence, scientists say, that the drug specifically fostered development of this mutation in HIV, later confirmed by clinical testing.

When researchers tested the blood of one of the co-infected patients for the M184V mutation, they found none in samples taken at the start of entecavir thereapy. But they did find it in 61 percent of viral samples tested after four months of therapy, and in 96 percent tested at six months.

Other Johns Hopkins investigators involved in this research, which was supported by funding from the National Institutes of Health, were Moira McMahon, Benjamin Jilck, Timothy Brennan, Lin Shen, Yan Zhou, Shridhar Bhat, Robert Hegarty, Curtis Chong and Jun Liu. Additional assistance from the Naval Medical Center in San Diego was provided by Braden Hale.

More than 1.2 million Americans are infected with hepatitis B. A vaccine against the virus has been available in the United States since 1982, but an estimated 60,000 new infections occurred in the United States in 2004 alone. Hepatitis B is transmitted by contact with blood and other body fluids of an infected person through sexual activities, injection drug use, sharing of personal care items or direct contact.

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