The current standard-of-care treatment for hepatitis C is interferon treatments, which aim to inhibit the ability of cells to host the virus. Studies have shown that certain ethnic groups like African-Americans and Hispanics are less likely to respond to interferon treatments.

Drug giants Vertex and Merck are now jockeying to assume market supremacy in a new class of hepatitis drugs. Both companies are currently developing protease inhibitors that directly target the hepatitis C virus.

But when comparing the two companies’ compounds, the devil is in the details. An ‘apples and oranges’ problem was highlighted on the pharmaceutical blog In Vivo. In its RESPOND-2 study, Merck defines a null responding patient — someone who is faring the worst under the current standard of care — as a patient whose viral load decreased less than 1 log after four weeks of standard treatment. That’s a considerably different criteria from the US Food and Drug Administration, which defines null responders as ‘less than a 2 log10 reduction in HCV RNA at week 12’. Vertex used the FDA’s definition of null responder in its study, REALIZE. Since both companies are trying to show that their protease inhibitor works better for patients for whom current options have failed, there is a remote chance that Merck’s numbers might paint an artificially rosier picture.

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