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Injection Approved for Neutering Dogs
Veterinary & Aquatic Services Department, Drs. Foster & Smith
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May 2003 News

The U.S. Food and Drug Administration (FDA) has approved an injectable medication used to neuter dogs between the ages of 3 and 10 months. Neutersol® (zinc gluconate neutralized by arginine) is the world's first injectable neutering drug for puppies. Its exact mechanism of action is unknown.

puppy positioned on back receiving Neutersol injectionTo administer the injection, the puppy is positioned on his back and properly restrained (chemical restraint may be used, if necessary, to prevent the dog from moving during the injection), and the veterinarian injects Neutersol into each of the testicles. The exact dose is pre-calibrated by measuring the width of the puppy's testicles using a custom dosing caliper.

In studies, Neutersol was found to be 99.6% effective in achieving sterilization. Mild, temporary swelling of the testicles is an expected reaction to the injection and usually occurs within 24-48 hours after injection. A puppy's testicles may remain slightly enlarged, but non-painful for a few months after the injection.

Other possible side effects include vomiting, anorexia, lethargy, diarrhea, and swelling and pain of the scrotum. Most reactions were seen within the first 7 days after the injection. Pain was most commonly seen in the first 2 days.

To minimize the occurrence of adverse reactions, such as scrotal irritation, inflammation, or infection, the manufacturer recommends that the puppy's activity post-injection be closely monitored, and that all necessary precautions should be taken to prevent injury to the testicles and to prevent the puppy from licking or biting the scrotal area.

For seven days after release from the veterinary facility, the manufacturer makes the following recommendations:

  • Restrict the puppy's exercise to leash walking.
  • Do not allow the puppy to run, jump, or engage in play activity.
  • Do not allow the puppy to lay on hard or wet surfaces.
  • Do not allow the puppy to lick or bite the scrotal area.

Dogs neutered by using Neutersol may still produce testosterone, which places them at risk of developing prostatic disease and testicular tumors. Testosterone-related behaviors such as aggression, mounting, roaming, and urine marking can also occur. Neutersol may not kill the sperm present at the time of injection in puppies. Therefore, you should keep your dog away from females in heat for at least 60 days after the injection.

Neutersol should not be used in dogs with undescended testicles, testicular disease or malformation, a history of allergic reactions to ingredients in the product, or irritation or skin lesions on the scrotum.

The manufacturer claims the benefits of the product include elimination of the need for general anesthesia, and speed of the procedure. The cost of the product is comparable to the costs of a surgical neuter.

Comments from Our Veterinary Staff…

Neutersol will prevent the development of sperm and the ability of the dog to impregnate a female, however, it has none of the other benefits of surgical neutering. While Neutersol may appear to be a good alternative to surgical neutering, it has considerable drawbacks:

  • Surgically neutered dogs have no risk of testicular cancer and a very low risk of prostatic disease. Dogs neutered through the use of Neutersol are still at risk for these two serious diseases.

  • Surgically neutering dogs can help prevent or eliminate testosterone-related behaviors such as aggression, mounting, roaming, and urine marking in the majority of dogs. This is not the case when using Neutersol. This is a major drawback.

  • Using Neutersol will probably not save you money since it will cost approximately the same as a surgical neuter.

  • Neutersol is not painless and some type of restraint, probably through the use of a tranquilizer or short-acting anesthetic, may be needed. Depending upon what is used, the puppy may be required to remain in the veterinary hospital for monitoring during recovery. Additional pain medication may be needed following the procedure.

  • At this time, the age at which Neutersol may be used is limited.

  • Aftercare after Neutersol injection is at least as restrictive as aftercare following surgery, if not more so.

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