(Reuters) – Achillion Pharmaceuticals Inc said its experimental hepatitis C drug showed promising interim data in a mid-stage trial, sending its shares higher in extended trade.

The company said the drug sovaprevir, when given along with the standard therapy of pegylated interferon and ribavirin, showed no detectable virus level in a majority of patients four weeks after the end of the treatment period.

Of the 39 patients who received 12 weeks of additional standard therapy following 12 weeks of the combination therapy, a total of 33 patients in three different dosage arms showed sustained viral response a month later.

Trial results from the same patients at 12 weeks post treatment, as well as from another arm where 14 patients received 36 weeks of standard treatment following combination therapy, are expected in the first quarter of 2013.

Additionally, the company said it has begun early studies to evaluate the safety of another one of its experimental hepatitis C drugs, codenamed ACH-3102, and expects to report initial results from this in the third quarter.

“The safety and tolerability seen to date with ACH-3102 … lead us to believe we have an in-house portfolio of optimized compounds that can successfully create an all-oral, interferon-free regimen for the treatment of genotype 1 HCV,” Achillion’s chief scientific officer Milind Deshpande said in a statement.

Hepatitis C drugmakers have been scouting for ways to develop an effective drug that does not contain interferon, which causes flu-like symptoms that often lead patients to discontinue treatment.

Companies such as Vertex Pharmaceuticals Inc, Bristol Myers-Squibb and Abbott Pharmaceuticals are currently in the race to get such a treatment to market.

Shares of New Haven, Connecticut-based Achillion rose 15 cents to $7.05 in after-market trade on Tuesday. They had closed at $6.90 on the Nasdaq.

(Reporting by Zeba Siddiqui in Bangalore; Editing by Anthony Kurian)