Sildenafil, the generic version of the drug known as Viagra, could be the long-waited remedy for a group of dogs with a rare disorder called megaesophagus, according to US research.

The condition involves an enlargement of the esophagus and a loss of the organ’s ability to move food to the stomach, which leaves food bottling up in the lower esophagus. If left untreated, many animals regurgitate their food and aspirate food into their lungs, causing aspiration pneumonia.

“The literature tells us that many dogs with the disease die from aspiration pneumonia or are humanely euthanised due to poor quality of life within eight months of diagnosis,” said Dr Jillian Haines, a veterinarian at Washington State University who co-led the study, published in the American Journal of Veterinary Research.

Liquid sildenafil was shown to relax the smooth muscle of the lower esophagus so it will open to let food pass to the stomach. Besides some rare gastrointestinal irritation, there are no side effects at the dose used in the study. 

While sildenafil is most known to treat erectile dysfunction, the drug is also used to treat elevated pulmonary blood pressure in dogs and humans.

“If you look at the literature, there are no drugs we can use to manage megaesophagus. Sildenafil is the first to target these mechanisms and reduce regurgitation, which is big because that’s what ultimately kills these dogs,” Dr Haines said. 

“It opens the lower esophageal sphincter for 20 minutes to an hour, which works really well for dogs because we only want that to open when they are eating.”

Dr Haines and her team used videofluoroscopy to monitor liquid and later, blended wet food as it travelled down the esophagus. 

Ten dogs with megaesophagus enrolled in the study were administered either a placebo or sildenafil for two weeks at a time. The dogs then went one week without either drug. Then the placebo and sildenafil groups were switched.

Their owners were tasked with logging regurgitation episodes but were not informed of which drug their dog had been taking.

There wasn’t a significant difference between the placebo and sildenafil during a 30-minute videofluoroscopy, where veterinarians use a moving X-ray to examine how food is swallowed. However, the study found nine out of the 10 owners reported reduced regurgitation during the two weeks when liquid sildenafil was administered.

“In many cases, the owners were able to figure out which drug was sildenafil because it was working,” Dr Haines said.

The dogs enrolled also gained an average of a little more than two pounds by the study’s end.

“Moderately affected dogs that were regurgitating frequently but not excessively seemed to see the most dramatic results,” Dr Haines said.

Dogs that showed severe signs of the disease didn’t show as positive of results. In those cases, the researchers found it was harder to get the drug into the stomach for absorption.

While the study is promising, much is still to be known about the drug. Dr Haines hopes future studies will investigate sildenafil’s use in veterinary medicine.