Gilead Sciences AIDs drug Viread (tenofovir disoproxil fumarate) has been given the green light in the US for treating chronic hepatitis B, just months after gaining European approval.

The approvals were based on data from two ongoing clinical trials, which compared Viread to Gilead’s other hep B drug Hepsera (adefovir dipivoxil). Results showed significantly more patients achieved a “complete response” when treated with Viread than with Hepsera.

"The approval of Viread for hepatitis B represents more than a decade of work in both the fields of HIV and hepatitis B to develop a medication that offers significant viral suppression, once-daily dosing and a well-established safety profile,” Gilead executive vice president of commercial operations Kevin Young said.

The thumbs-up marks a big expansion in the hepatic market for the California-based company. Gilead’s first hep B drug Hepsera notched up $90 million worth of sales in the second quarter. According to a RBC Capital Markets analyst Jason Kantor, quoted in Reuters, the hep B market was underserved with Hepsera having a 44% market share.

Hepatitis B is believed to affect about 400-million people worldwide.

Viread was approved in the US as a treatment for HIV in 2001 and was the first in a new class of compounds called nucleotide analogs. As a hep B treatment the once-daily drug works by blocking the hepatitis B virus DNA polymerase, which is the enzyme necessary for the virus to replicate in liver cells.

Gilead is also developing a treatment for hepatitis C and a hepotoprotectant for multiple forms of hepatitis-related liver fibrosis.

Gilead back in court over improper marketing
Meanwhile, the US has reinstated a securities fraud claim against Gilead over improper marketing of Viread as an HIV treatment. Investors claimed Viread was being marketed for off-label uses and stock was being inflated in 2003.

In 2006, the case had been dismissed by the US district court because of a lack of evidence that stock losses were a result of off-label sales. This decision was reversed by the Ninth US Circuit Court of Appeals.

According to the appeals court, "Gilead's fortunes, as reflected in its stock price, depended heavily on Viread's commercial success. Ultimately, 75% to 95% of Viread sales resulted from off-label marketing efforts.

“The company and its officers emphasized to the public that they carefully complied with federal and state regulations, when in fact they knew that they were acting unlawfully by aggressively marketing Viread for off-label uses."

Gilead was unavailable for comment at time of publishing.