The condition primarily affects male cats because of their narrow urethras, but it can happen in females, too. And it’s considered common: about 10 percent of felines will have a urethral obstruction. Photo: Lightspruch / Shutterstock

A new study from a Cummings School resident found an oft-prescribed drug to treat urethral obstruction in cats is ineffective, adding to mounting research that shows why it should not be used   

When a cat feels nature’s call, it heads to the litter box for relief. But what if nothing comes out? The problem could be a urethral obstruction, a life-threatening condition that prevents cats from urinating.

When the urethra is blocked, urine backs up in the cat’s bladder, causing toxins to build in the blood. When treated in a timely manner the prognosis is generally good, but left untreated, it shuts down the kidneys and can be fatal . The condition primarily affects male cats because of their narrow urethras, which are about the diameter of pencil lead , but it can happen in females, too. And it’s considered common: about 10 percent of felines will have a urethral obstruction, and it’s more prevalent in cats with lower urinary tract disease.

For years, veterinarians have prescribed a drug called prazosin to treat cats with recurring urethral obstructions. However, recent research has shown prazosin, which is in the category of antihypertensives, to be ineffective. David Conway, a resident in the Emergency and Critical Care Service at the Henry & Lois Foster Hospital for Small Animals, wanted to find a better way to treat his feline patients.

“Prazosin is a medication that blocks a receptor called the alpha receptor, which can be found in blood vessels and the urethra,” he says. “For decades, the theory was that this medication would block those receptors, allowing the urethra to relax and the cat to urinate again. But the most recent evidence, including our work, suggests that is not the case.”

He launched a study of more than 380 cats with urethral obstructions, and the results were recently published in the Journal of the American Veterinary Medical Association. Most of the cases came through the Foster Hospital for Small Animals, but some were enrolled from other internal medicine and critical care veterinary centers across the country.

“We set up a system where we either always gave prazosin or never gave prazosin to cats with urethral obstructions, because the key thing we wanted to do was see if this drug helped,” says Conway. “We also collected data about the cat’s age, lifestyle, body weight, what other drugs they given, how were they unblocked, and how long they had a catheter. The prazosin use was the key difference between the groups that reobstructed and did not reobstruct.”

His goal with the study, which was co-authored by Elizabeth Rozanski, associate professor at Cummings School of Veterinary Medicine and member of the Emergency and Critical Care team, is to get attention off prazosin and onto other treatments or therapies that have a greater chance of being beneficial.

When cats have a urethral obstruction, they may strain to urinate, have blood in their urine, or cry out in pain. They may hide, not eat, or vomit. Though the exact cause isn’t known, there are a few factors that can contribute to urethral obstructions, including urinary stones, urinary tract infections, and urinary tract tumors. These contributing factors as well as urethral obstructions can occur in cats of any age, though older cats may be more prone to the conditions. In young cats, non-infectious inflammation is the leading cause of urethral obstruction , and stress, diet, weight, and activity can all play some role, Conway says. It’s important to reduce stress, give cats plenty of places to hide, and make sure they drink enough water. 

Diet modification can help as a long-term strategy, as cats with recurring urethral obstructions have fluid and electrolyte needs. For some cats with urinary tract disease, especially recurrent issues, Conway recommends commercially available prescription diets that are designed to increase water consumption or have a mineral balance that decreases stone formation in the urine. Other treatments include non-steroidal anti-inflammatory medications (NSAIDs), which may be beneficial in reducing inflammation but require consideration before use in animals with urinary issues because they can harm the kidneys, or a therapy in which a class of proteins called glycans are put into the bladder .

“The problem is that treatments can become expensive for owners,” Conway says. “We are especially interested in preventing recurrence because once this happens three, four, or five times in a cat’s life, that is a financial burden for humans and a health burden to the cat.”