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U.S. Department of Health and Human Services

Animal & Veterinary

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FDA Approves First Injectable Solution for Sterilization in Dogs

FDA Veterinarian Newsletter July/August 2003 Volume XVIII, No 4

FDA has approved the first product for chemical sterilization of 3 to 10 month old male puppies. The drug, Neutersol Injectable Solution (zinc gluconate neutralized by arginine), provides an alternative to surgical castration and may prove to be a valuable aid in efforts to control burgeoning dog populations.

Neutersol, administered by direct injection into the testicles, is a necrotizing agent that has a local effect when injected into the testicle. Based on histopathology, one or more of the following actions accounts for the drug’s effectiveness: 1) Atrophy of the testicles, epididymides, seminiferous tubules, and prostate gland and 2) Scar tissue formation which prevents movement of sperm from the seminiferous tubules to the epididymis. Neutersol does not require the use of general anesthesia, though sedation is recommended to prevent the dog from moving during injection.

The effectiveness of Neutersol was evaluated in a field study of 270 male puppies between 3 and 10 months of age. Of the 270 puppies enrolled, 224 completed the study to month 6 and were included in the analysis. One injection of Neutersol in each testicle produced successful chemical sterilization in 223/224 (99.6%) puppies, as determined by serial semen analyses. In a study conducted in laboratory beagles, effectiveness was confirmed up to 24 months post-injection.

Proper injection technique and post-injection care are critical for the safe use of the product. According to Dr. Elizabeth Luddy, veterinary medical officer at CVM, “The most serious reaction we saw in laboratory and field testing was ulceration of the scrotum at the injection site, associated with incorrect injection technique, movement of the needle during injection or the dog licking or biting the area after injection.” To help educate veterinarians and dog owners about these and other safety issues and to prevent the occurrence of serious adverse events, the approved labeling includes an instructional videotape demonstrating the proper injection technique, and a client information sheet explaining the importance of post-injection monitoring and care.

Unlike surgical castration, dogs treated with Neutersol become sterile without removal of the testicles and, therefore, testosterone is not completely eliminated. Veterinarians and dog owners should be aware that diseases which occur as a result of or in conjunction with testosterone hormones (prostatic disease, testicular or perianal tumors) may not be prevented with this procedure. As with surgical castration, secondary male characteristics (roaming, marking, aggression, or mounting) may be displayed.

Neutersol is manufactured by Meridian Medical Technologies, Inc. for Technology Transfer, Inc., Columbia, MO and is available for use only by or on the order of a licensed veterinarian.