A tale of two Ebola stocks: Chimerix and Tekmira

The Ebola story has played out in the stock market recently largely on the backs of two companies: drugmakers Chimerix and Tekmira, which in recent days have started to move in coordinated and opposite directions.

That's because their drugs are the most frequently discussed in terms of potential use in American Ebola patients, after supply of the experimental therapy ZMapp, made by closely held Mapp Biopharma, was exhausted.

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Tekmira's drug, TKM-Ebola, was used in Dr. Rick Sacra, an American who was flown back from Liberia to Nebraska Medical Center for treatment, the same facility now treating NBC News freelance cameraman Ashoka Mukpo. Sacra recovered, though doctors say it's impossible to know what role, if any, the experimental therapy played; he also received donated blood from Ebola survivor Dr. Kent Brantly, as well as supportive care.

Chimerix's drug, brincidofovir, has recently grabbed the headlines, seemingly out of nowhere. And that's when the stock market started to link these two companies.

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Brincidofovir is in late-stage testing at Chimerix for other kinds of viruses, like adenovirus and cytomegalovirus, and has been used in more than 1,000 patients. That means its safety profile is understood, something that appeals to doctors using unapproved drugs in emergency situations; medicine's first tenet, of course, is to do no harm.

It was only recently that brincidofovir showed some potential for treating Ebola. On Sept. 3, Chimerix said the therapy showed in vitro activity against the virus in testing at the Viral Special Pathogens Branch of the Centers for Disease Control and Prevention and National Institutes of Health. That means it showed potential in a test tube. Additional animal model studies were underway. The drug's effectiveness in humans is unknown.

Meanwhile, in response to questions about experimental drugs in the last week, CDC director Dr. Tom Frieden primarily mentioned ZMapp and TKM-Ebola, noting Tekmira's therapy has some initial side effects that may make patients feel worse at the onset of treatmentsomething that could deter doctors from using it in already very sick patients.

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Then Monday, Oct. 6, Chimerix said emergency use of brincidofovir had been authorized by the Food and Drug Administration for use in Ebola patients, at the request of treating physicians. Later the same day, Texas Presbyterian Hospital in Dallas said the drug was being used in Thomas Eric Duncan, the only person to have been diagnosed with Ebola on U.S. soil. Chimerix's stock jumped. Tekmira's sank.

"Did the Ebola field just get leapfrogged by Chimerix?" Piper Jaffray analyst Josh Schimmer asked in a research note Monday. Schimmer had highlighted the drug's potential for use in Ebola the previous week.

Fighting Ebola   

The next day, another surprise: Mukpo, being treated in Nebraska, would also receive brincidofovir.

"After looking at the data on this drug, collaborating with the CDC and FDA and speaking with the patient and his family, we decided this was currently our best option for treatment," Phil Smith, medical director of Nebraska Medical Center's Biocontainment Unit, said in a statement. "Every patient is somewhat different, and we believe brincidofovir is the best choice."

Chimerix again rose. Tekmira again dropped—many were presumably counting on Nebraska to again draw upon TKM-Ebola, especially as Mukpo was in more stable condition than Duncan.

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Then on Wednesday, Texas Presbyterian released the news that Duncan had passed away. Questions swirled—and continue to—about his treatment, the delay in care he received at the hospital, and, of course, the implications for brincidofovir's efficacy against Ebola.

"Chimerix shares are likely to be (awkwardly) tracking the fate of the Ebola outbreak and treated patients," Piper's Schimmer wrote in a research note. "Ultimately, the utility of brin for treating Ebola and other diseases will be defined by animal models and potentially larger human clinical trials, as opposed to n=1 experiences."

In other words, still not enough is understood about the way Chimerix's drug works in people to conclude whether it works for Ebola. Because of its demonstrated safety profile, and the fact that it's a pill (which is easier to manufacture than a large molecule biologic, like ZMapp; or TKM-Ebola, which uses a technology called RNA interference) and can be stored at room temperature, hopes are high. But there is still more work to do before this drug, and any of the others—including Tekmira's—are understood in Ebola.