Clinical Studies

sildenafil in canine megaesophagus
Efficacy of liquid sildenafil as a novel treatment for canine generalized megaesophagus: a randomized crossover study


Purpose of Study

This study is designed to assess if the drug sildenafil could work to relax the lower esophageal sphincter in dogs, allowing food to pass more easily from the esophagus into the stomach. This would potentially reduce the frequency of regurgitation, allowing dogs to have better quality of life, reduced risk of aspiration pneumonia, and lower rates of death/euthanasia.


  • If sildenafil is found to be effective in allowing food to pass more quickly into the stomach of dogs with megaesophagus, it may be a feasible management strategy for this population of dogs. If effective, it could potentially reduce frequency of regurgitation episodes; reduce the risk of aspiration pneumonia, and lower rates of death/euthanasia while also improving overall quality of life for dogs and their owners.
  • This clinical study will cover the cost for a CBC, biochemistry panel, urinalysis, chest x-rays, videofluoroscopy, additional blood tests as needed to evaluate the cause of megaesophagus, and medications. The total cost of services paid for by the study is approximately $600.00.

Enrollment Requirements

To be enrolled, your dog must have previously been diagnosed with megaesophagus; older than 1 year of age; and otherwise healthy with no change in clinical signs within the previous 3 months.  Dogs with myasthenia gravis requiring medication will not be eligible for this study. Successful study candidates must be comfortable eating around people they don’t know and sitting in a Bailey chair.

Study Schedule

Once enrolled, you will be asked to keep a record of your dog’s regurgitation characteristics at home for 2 weeks prior to your first visit. 

Following this 2-week period, your dog will come to Washington State University’s Veterinary Teaching Hospital (WSU VTH) for a 2-day appointment.  On Day 1, your dog will have bloodwork and chest x-rays, and will be given water and food mixed with contrast agent while a fluoroscopy (x-ray video) is performed. Day 2, your dog will receive either sildenafil or a placebo followed by food and fluoroscopy will be repeated.

After this first appointment, you and your dog will return home where you will give your dog the assigned medication for 2 weeks and keep a written record of your dog’s regurgitation characteristics for 3 weeks (2 weeks on medication and 1 week off).

You and your dog will then return to the WSU VTH for appointment Day 3. Your dog will be given the opposite medication they received on day 2 and we will again have repeat fluoroscopy (the same as Day 2).

We will send you and your dog home with a 2-week supply of the opposite medication they first received and you will be asked to keep a record of your dog’s regurgitation characteristics for a final 3 weeks and email that record to us.  Once we have received this final documentation of your dog’s regurgitation characteristics, your study participation will be completed.

At the end of the study, once the researchers are no longer blinded, we will share your dog’s individual results with you.  This may help you make a decision about potentially continuing the use of sildenafil in your dog or making other changes to dietary management.    

Owner Responsibilities

For this study, you will be required to bring your dog to WSU VTH for a total of 3 study appointments: the first 2 appointments on back-to-back days.  You will also be asked to keep a record of your dog’s regurgitation characteristics (frequency, content, etc) for a total of 8 weeks during the study period and give your dog an assigned medication, twice daily for 4 of those 8 weeks.

Contact Information

For more information please contact Valorie Wiss, Clinical Studies Coordinator. 

(Office: 509-335-0798, Cell: 509-432-5345 or