To date, and for obvious reasons given anatomical structures, non-surgical sterilants targeting the gonads have been limited to male dogs and cats. They involve injecting a chemical agent into the testis or, less often, the epididymis or vas deferens, to cause azoospermia and sterility. Intratesticular injectable sterilants for male cats and dogs have been studied for more than five decades, with a variety of chemical agents explored over the years. Today there are two approaches that are being used and/or studied most extensively. 

The first approach entails zinc gluconate-based solutions, which cause testicular degeneration and permanent sterility. The most well known of these, Zeuterin™ (zinc gluconate neutralized with L-arginine), is approved by the U.S. Food & Drug Administration (FDA) for sterilization of male dogs. It became commercially available in the United States in February 2014, and was also approved for male dogs in Colombia, Panama, Mexico, and Turkey. (Please note that as of 2016 the product is no longer being produced or distributed). Whereas products that suppress GnRH also suppress sex hormones, Zeuterin does not stop testosterone production. (More information can be found in ACC&D’s Zeuterin Product Profile and Position Paper.) 

Two additional zinc gluconate-based solutions, Infertile® and Testoblock®, have been studied in Brazil and are further described in Contraception and Fertility Control in Cats and Dogs. To the best of our knowledge, they are not currently commercially available in any country.

Calcium chloride-based compounds (mixed with either alcohol or lidocaine) are also being studied for sterilizing male dogs and cats. This is not presently approved by any regulatory agency, and it is created through compounding ingredients. ACC&D believes that the current use of calcium chloride as an injectable sterilant is experimental.

As a broad category, chemical castration has multiple strengths. The technique can be inexpensive, particularly relative to surgical castration. It can be performed humanely without general anesthesia, as well as without sophisticated clinical facilities or skilled veterinary surgeons. All of these features make intratesticular injectable sterilants an incredibly attractive option for sterilizing more animals, more effectively utilizing resources, and saving many more animals’ lives by preventing unwanted births.

Even so, ACC&D strongly advocates prudent use of intratesticular injectable sterilants. With Zeuterin, the procedure was relatively easy, but it was also precise and required proper injection technique. When treating free-roaming dogs, it is important that someone observe the animal following the procedure and, on the chance that an adverse reaction occurs, to have a skilled veterinary professional who can provide treatment.