CAMBRIDGE, Mass. ( TheStreet) -- Vertex Pharmaceuticals ( VRTX - Get Report) said Tuesday that 75% of hepatitis C patients never treated before achieved a viral cure after receiving a 12-week course of the company's experimental drug telaprevir plus the current standard of care, according to results from a phase III study.

Vertex and its partner Johnson & Johnson ( JNJ - Get Report) plan to seek regulatory approval for telaprevir in the second half of the year, based on positive results from the so-called Advance study.

Telaprevir represents a major medical advance in the treatment of hepatitis C, a chronic, progressive disease that affects the liver. Telaprevir acts directly against the virus that causes hepatitis C, and in doing so, increases the number of people who can be cured of the disease while also shortening treatment to six months from a year.

The 75% cure rate for patients treated with telaprevir in the Advance study released Tuesday compares to a 44% cure rate for patients treated for a year with only the current standard of care -- long-acting interferon and ribavirin.

Investors were largely expecting a telaprevir cure rate in the 70% range from the Advance study.

"These first Phase 3 results are important for people with hepatitis C, as they represent a potential new era of therapy where doctors may be able to use direct acting antiviral medicines to improve treatment and help patients potentially avoid life-threatening liver-related consequences associated with chronic hepatitis C," said Dr. Ira Jacobson of Weill Cornell Medical College and an investigator in the Advance trial, in a statement.

The Advance study enrolled 1,095 patients infected with chronic hepatitis C who had not previously been treated. Patients were randomized to one of three different treatment regimens. One group received 12 weeks of telaprevir plus standard of care followed by 12 weeks of standard of care. A second group received 8 weeks of telaprevir plus standard of care followed by 16 weeks of standard of care. A third group of patients were the control for the study, receiving standard of care for a full 48 weeks.

As discussed above, 75% of the patients in the so-called "12+12" arm achieved a viral cure rate, defined as undetectable levels of virus measured six months after treatment stopped. The viral cure rate for the shorter, 8-week telaprevir regimen was 69%, while 44% of control patients treated with just standard of care achieved a viral cure. These results were statistically significant in favor of telaprevir.

Patients treated with telaprevir for 12 weeks relapsed at a rate of 8.6% compared to a 28% relapse rate for patients treated with standard of care only. Between 6.9% and 7.7% of telaprevir-treated patients discontinued the study due to adverse events. This included a 1.4% discontinuation rate due to rash among telaprevir patients.

Vertex described the discontinuation rate for telaprevir patients as "low," compared to previous studies. Telaprevir has been linked to rash in patients in prior studies, but the rash-related discontinuation rate in the Advance study fell as doctors were better able to manage the side effect.

With the Advance study results released, investors now await Merck ( MRK) to announce results from a phase III study of its own hepatitis C drug -- and potential telaprevier competitor -- known as boceprevir.

Vertex is running two additional phase III studies of telaprevir, including a study of treatment-resistant hepatitis C patients.

-- Reported by Adam Feuerstein in Boston.

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