Merck (MRK -0.44%) has high hopes for gefapixant, an experimental drug that it's referred to as a "pipeline in a product." However, the U.S. Food and Drug Administration (FDA) recently poured some cold water on those hopes, turning down approval for the drug in treating chronic cough. In this Motley Fool Live video, recorded on Jan. 26, Fool contributors Keith Speights and Brian Orelli discuss why the FDA gave a thumbs-down to gefapixant.

Keith Speights: Pfizer (PFE 0.12%) wasn't the only big drugmaker to get slapped down by the FDA recently. The agency also rejected Merck's application for approval of gefapixant in treating chronic cough.

Merck has referred to this drug at times as "pipeline in a product" because it could be used for so many different indications. What happened here Brian?

Brian Orelli: So at least Merck gave some information. Merck said that according to FDA, requested additional information related to the measurement of efficacy.

My initial thought was maybe the endpoint was patient-derived and we've seen a lot of issues with patient-derived endpoints. Maybe they were measuring, did the patient feel like their cough got better.

But Merck also uses coughs per hour using a 24-hour sound recording device. That's a substantially more objective measure of coughs than having a patient-derived endpoint.

So given the strong placebo, there was a strong placebo effect in this clinical trial. Given that, it seems like maybe the FDA might be more concerned that the measurements of coughs per hour in sounds recordings, might not be the best endpoint since people who got the placebo also had a reduction in the number of coughs.

That could be a major blow, which could result in potentially even a new clinical trial. Any changes in the FDA's requirements for clinical endpoints for coughs could also affect Bellus (BLU), the ticker BLU, which is also developing a treatment for cough.

Speights: This just comes with the territory for these big companies. Companies like Pfizer and Merck know that they're not going to win on every drug that they move forward. But Merck really was counting on this one being successful, and they certainly haven't thrown in the towel, they still have high hopes for this drug.