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A One-Shot Deal?

FDA approves sale of drug that sterilizes male animals without surgery, but the limitations of Neutersol may lead shelters to keep neutering the old-fashioned way

FDA approves sale of drug that sterilizes male animals without surgery, but the limitations of Neutersol may lead shelters to keep neutering the old-fashioned way

Giving a new meaning to the term “shrinkage,” the Food and Drug Administration (FDA) took the first step toward the chemical sterilization of pets with their recent approval of the testicle- and prostate-shrinking drug Neutersol for male puppies ages three to ten months.

In contrast to standard surgical castration, which removes the testicles, Neutersol is a zinc and l-arginine-based compound injected into each testicle, causing them and the prostate to atrophy. With just one quick shot, which costs approximately $50, the solution causes permanent sterility. Although anesthesia is not required to administer the drug, sedation may be required for puppies who move too much to be injected properly. In addition, because Neutersol may not kill the sperm present at the time of injection, treated dogs should be kept away from females in heat for at least 60 days after the procedure.

“Our primary job is to get these dogs sterilized so our shelters won’t have to do so many euthanasias,” said Dr. Bruce Addison, the founder of Addison Biological Laboratories, the exclusive marketer of the drug. “We would like to see more people comply with neutering, and the convenience [of Neutersol] we hope will lead to compliance.”

The use of Neutersol, however, will not totally shut down testosterone production in dogs, leaving the possibility that the drug will not eliminate hormone-related illnesses such as testicular cancer or prostate disease—both of which can be prevented through surgical neutering.

Addison said his company is addressing the issue with the FDA. While he doesn’t want to jump too far ahead of the FDA’s review of their research, he suspects that the testicular cancer will not be an issue for chemically sterilized dogs because Neutersol atrophies the testicles by 77 percent, eliminating most of the cells that could potentially cause cancer.

Also yet to be tested is the effect of chemical sterilization on behavior; the continual production of testosterone following injection may not do anything to help decrease unwanted secondary male behavioral characteristics—such as roaming, marking, and aggression—that surgical castration is often thought to tackle. While Neutersol produces a 41- to 52-percent decrease in testosterone levels and could lead to some of the same positive behavioral effects as surgical castration, no tests have been done to study dog behavior after the use of the drug. Because of the lack of research in that area, Addison said he cannot make any claims about Neutersol’s effect on behavior.

As of press time, news of Neutersol’s debut was just beginning to trickle out to the sheltering community. As with any new product, reactions have ranged from naysaying to excitement to cautious optimism.

While the price tag for Neutersol may be acceptable for private practice veterinarians, some nonprofit organizations and municipal agencies are finding the drug’s time-saving qualities aren’t enough to justify its cost.

“The price is definitely more than what we expected,” says Karen Sommer, the president of the Lakeland SPCA in Florida. “I don’t know at this point whether or not it truly is a viable alternative to surgical castration. My veterinarian can do a neuter in nine minutes, after the techs had the dog scrubbed and shaved the dog, so I don’t know that I’d be saving much time, especially if there is prepping that needs to be done before (using Neutersol). While I do feel like Neutersol is an avenue worth exploring, I want to see how our initial run goes.”

Sommer had just gotten the drug when she was contacted by Animal Sheltering and hadn’t used it yet. But her shelter was planning to do an initial test run, with assistance from Addison Biological Labs, on ten dogs who would go up for adoption after being sterilized. Staff will tell adopters about the new sterilization method and will follow up in the weeks after the dogs are adopted to see how they’re doing, both physically and behaviorally.

Some in the sheltering community, however, think any time shelter personnel can save—and any animal stress they can reduce—is definitely worth the cost of the new drug.

“To me $50 is cheaper by the time you add up payroll, instruments, and all the rest, as well as the benefits to the animal of having the procedure possibly be less stressful,” says Darlene Larson, who used to run a shelter but now is a director with the National Animal Control Association and works for the National Council on Pet Population Study and Policy. “I personally think it’s pretty exciting. It’s a first step to altering animals without surgery.”

Side effects include testicle swelling within 24 hours of injection—a normal reaction to the compound—in addition to possible vomiting, loss of appetite, lethargy, and diarrhea.

Given that Neutersol’s use is currently limited to puppies ages three to ten months, Addison said the company is moving forward with testing the drug on both older dogs and cats. Scientists have tried chemical sterilization on these populations in the past, but the results thus far have been mixed. The HSUS has been actively involved in pursuing alternatives to surgical spaying and neutering for decades, and worked with the late Dr. Mostafa S. Fahim, the developer of Neutersol, in early field trials of the product. While The HSUS is excited about the future possibilities of chemical sterilization, the procedure is still in the beginning stages. Because of the drug’s limited application to puppies and some lingering questions about its effects on behavior and health, it could be years before Neutersol becomes a fully viable alternative to surgical neutering of shelter animals.


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