Eiger BioPharmaceuticals Inc.'s experimental drug, pegylated interferon lambda, reduced viral load in a mid-stage study on patients infected with the Hepatitis Delta virus.

The infection, caused by the Hepatitis Delta virus, or HDV, occurs only in patients already harboring Hepatitis B virus and leads to more severe liver disease.

The study, called LIMT HDV, tested two doses of the pegylated interferon lambda injection among 33 patients from New Zealand, Israel and Pakistan. Interferons are proteins manufactured and released by body's cells when they get infected with viruses, bacteria, parasites, or tumor cells.

Results showed that after 48 weeks of treatment, both the doses of pegylated interferon lambda, also known as Lambda, led to either a reduction in the viral load or non-detection of any HDV-RNA.

Lambda enhances the retention time of treatments by protecting them against degrading inside a cell, which consequently improves their therapeutic potential.

The most common side effects from the treatment included mild to moderate flu-like symptoms and higher levels of transaminase enzymes — a potential sign of liver disease.

Lambda was better tolerated by HDV infected patients who were previously treated with alfa interferon, said study co-lead investigators Ohad Etzion and Saeed Hamid.

The drug's lower side effects also make it attractive for use as a monotherapy or in combination with other HDV treatments, they added.

There is currently no approved therapy for HDV infection, which affects up to about 15 million to 20 million people worldwide, the company said. It is considered to be one of the most severe forms of viral hepatitis in humans.

The Palo Alto, Calif.-based company is conducting another phase 2 study, called LIFT, to test a combination of interferon lambda and its lead candidate lonafarnib boosted with approved HIV-1 treatment ritonavir among HDV-infected patients.