Vertex Pharmaceuticals (NASDAQ:VRTX) is on pace to hit its 2018 goal of about $3 billion in sales from its three cystic fibrosis drugs, but the biotech only has a fraction of the overall market. Its current drugs are approved to treat about 37,000 patients globally, but there are an estimated 24,000 additional patients with minimal function mutations that Vertex's current offerings aren't approved to help.

At least not yet.

Yesterday, the biotech released late-stage clinical trial data showing a new triple combination that adds VX-659 to two other drugs -- tezacaftor and ivacaftor. These are currently sold as Symdeko and can help patients who have one F508del mutation and one minimal function mutation -- so-called "het/min" patients.

Specifically, the triple combination improved lung function (measured using percent predicted forced expiratory volume in one second, or ppFEV1) by 13 percentage points after just four weeks of treatment compared to a 1 percentage-point decline for patients who received placebo. The 13-percentage-point improvement is better than the improvement of 11.6 percentage points seen in the phase 2 study.

Clipboard with paper labeled cystic fibrosis, medication, and a stethoscope on a table.

Image source: Getty Images.

Vertex also released data from a second study in patients with two F508del mutations. Those patients can be treated with Symdeko, but adding VX-659 on top of that doublet produced a substantial additional benefit, with the triple combination improving ppFEV1 by 10.2 percentage points compared to an improvement of 0.3 percentage points for patients who remained on Symdeko.

Both studies will continue to collect additional safety data since patients will be on the triple combination long term, but so far, the efficacy and safety appear to be solid enough to gain approval.

A no-lose situation

To increase its chances at success, Vertex actually is testing two sets of triple combinations. Data from another pair of phase 3 studies testing VX-445 plus the Symdeko combination are expected in the first quarter of 2019. While it's dangerous to compare across trials, especially small phase 2 studies, the VX-445 triple combination performed a little better than the VX-659 triple combination in their respective phase 2 studies.

Best case scenario, the VX-445 triple combination produces an even better improvement in ppFEV1 than VX-659 just posted, but even if it doesn't, Vertex already has the efficacy data necessary to gain Food and Drug Administration (FDA) approval for the VX-659 combination. No matter which one ends up winning, Vertex plans to file a marketing application with the FDA in the middle of next year, setting up an approval later in the year or the first half of 2020.

Looking further ahead, Vertex is working on VX-561, a variation of ivacaftor that only needs to be taken once a day. Vertex plans to run a dose-ranging study next year before moving into a phase 3 program swapping out twice-daily ivacaftor in the triple combination.

The VX-561 combination probably won't increase sales much -- patients just would be switching from one of the triple combinations in development -- but the added convenience of a once-daily treatment should help fight off competition from Galapagos and others if it emerges.

Brian Orelli has no position in any of the stocks mentioned. The Motley Fool recommends Vertex Pharmaceuticals. The Motley Fool has a disclosure policy.