( TheStreet) -- Vertex Pharmaceuticals (VRTX - Get Report) announced Tuesday night the design of two phase III studies for its combination therapy to treat the most common form of cystic fibrosis. The studies will each run for six months, so results could be ready as early as the end of 2013 or during first half of 2014.
If the studies are positive, Vertex intends to file for U.S. approval in 2014.
The combination therapy program is vital to Vertex's future growth because the form of cystic fibrosis targeted -- patients with a genetic mutation known as F508del -- make up about half of the 70,000 patients worldwide. Vertex's currently approved cystic fibrosis drug Kalydeco targets only 4% of patients with the G551D mutation. Kalydeco sales totaled $172 million in 2012.
The studies announced Tuesday will evaluate the two different doses of an experimental medicine VX-809 in combination with Kalydeco. Each study will enroll 500 cystic fibrosis patients randomized to either the VX-809/Kalydeco arms or a placebo for six months of treatment. The studies' primary endpoint will be the relative improvement in lung function of VX-809/Kalydeco compared to placebo.Last fall, Vertex presented data from a phase II study demonstrating that a 600 mg dose of VX-809 and Kalydeco worked synergistically to improve lung function in cystic fibrosis patients with the F508del mutation compared to placebo. This same dose combination will be tested in the phase III study along with a higher 800 mg (actually, 400 mg given twice a day) dose of VX-809 plus Kalydeco. Vertex also announced new data from this phase II study on Tuesday night showing similar lung function improvements between the 800 mg and 600 mg doses of VX-809. For this reason, the higher dose was included in the phase III studies. Along with the two phase III studies in adult patients, Vertex will also conduct a six-month study of the combination therapy in pediatric patients ages 6 to 11. This study, along with the data from the adult studies, may be used to expand the combination therapy's approval into younger patients. In January, FDA anointed Kalydeco and VX-809 with Breakthrough Therapy Designation as part of the agency's efforts to accelerate the development and approval of drugs for serious and life-threatening disease. Vertex did not say whether Breakthrough Designation played a specific role in the VX-809/Kalydeco phase III program but the relatively short six-month duration of the studies plus the ability to test the combination in children at the same time does accelerate the development of the combination therapy. If the data from the studies are positive, the drugs could be approved sooner than expected and for more patients. Vertex is conducting a phase II study of another experimental cystic fibrosis drug known as VX-661, which could be more potent than VX-809. Results are expected before the end of the second quarter. Ahead of Tuesday's announcement, Vertex shares closed down 1.5% to $44.18. The stock was up slightly in after-hours trading. -- Reported by Adam Feuerstein in Boston. Follow @AdamFeuerstein