Dear Dr. K;

Dear Dr. K;

I’ve seen you and multiple other doctors for what has been called unexplained chronic cough.  Now I’ve read about the new drug Gefapixant.  Do you think I’m a candidate?

My answer is a qualified yes. But before I continue my answer let me first give a summary of your own situation that might be of help to other kindred spirits.  Your cough is called “unexplained” because despite our best efforts the medical specialists you’ve seen have failed to find a cause.  Your primary doctor listened to your lungs (normal) and ordered a chest x-ray (normal) and a CT scan (normal).  Your ENT did nasal endoscopy and a sinus CT, both of which were normal.  Your allergist (me) did allergy tests that were negative.  Your pulmonary doctor did a series of breathing tests and even a methacholine challenge test, all of which were normal.  He did have you try some inhalers which did not stop your chronic cough.  Your gastroenterologist did an upper GI x-ray and then an endoscopy both of which were normal.  Your speech pathologist examined your larynx and vocal cords and found no abnormality.  And yet, you continue to cough. 

Gefapixant is an antagonist (blocker) of the P2RX3 receptor.  This receptor functions as a ligand-gated ion channel for nociceptor activation.  I’m sorry for all the big words, but basically a nociceptor is a sensor that tells a nerve that it is being stimulated.  This sensor is activated through an entrance doorway called an ion channel. 

As it turns out this particular receptor plays a role in sensing pain, sensing the need to empty our bladder and sensing the need to cough.  And you might correctly guess the medication is being studied for these applications as well. 

Compared to placebo Gefapixant 45mg twice a day reduced cough frequency and cough severity and improved cough-specific quality of life.  Its main side effect was causing taste perversion.

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