Jesus, I've done more than a little research, which led me here to see if any informal "phase 0 trials" had begun yet. Many an hour after work was spent with Google Scholar looking into the literature.
Let me set the stage: This is the third-generation zinc gluconate product that's on the market now; the initial version, Neutersol, was distributed too widely, too soon and ran into unexpected numbers of side effects. It was determined that aseptic procedure and injection technique were critically important in preventing side-effects, and that the use of ill-trained personnel was leading to zinc solution getting to the wrong place, and ablating the wrong tissue.
The second-generation product, Esterilsol, was distributed mostly overseas and if I recall, especially in Mexico. It changed the formula slightly, most significantly adding a small fraction of DMSO to the preparation, which serves as both a powerful anti-inflammatory, free-radical scavenger, and as a tissue permeator to ensure more complete distribution of the drug in the testicle. I'm not certain about any specifics about the protocol changing, however its approval was broader - instead of puppies under one, it was approved for all male dogs older than three months. It could work in cats, but tomcats can be fixed in about a minute by a skilled vet, so there was little demand for a faster way to do it.
The third generation product, Zeuterin, seems to retain the DMSO, and comes with a substantially different protocol, but a similar formula as far as I can tell. Because of the unforseen complications, substantial work was done to isolate the problem. The new protocol is much fiddlier than the simple injections recommended with earlier versions; they consider this injection to be a minor surgical procedure in complexity. As a result, the product is only sold to veterinarians that have been specifically trained in the process, though the training can be completed in an hour or so. The real advances have been to use not one but three sterile needles; one is used to aspirate the drug into syringes, but not to inject - any residue clinging to the needle could cause an abscess. After loading the syringe, the needle is detached, and a new one put in its place, this one used to inject the drug into only one testicle. The needle gauge must be extremely fine, and the injection extremely slow (at least 5 seconds) in order to prevent any leakage out of the testicle into the scrotum, either under pressure, or by triggering the nerves in the testicle (which detect pressure) to cause contraction.
And now that I've checked my materials, the new protocol was in place in the second-generation product, resulting in a significantly reduced rate of complications, comparable to or slightly lower than that of surgical castration (though the complications have a reputation for being more complex).
Esterilsol causes permanent, irreversible sterility relatively quickly by disrupting sperm production and causing sclerosis of the testicle's ducts, preventing the passage of any sperm that may still be produced. Testosterone is reduced from 48-52%, as while the Leydig cells aren't destroyed, without sperm production ongoing, the pituitary no longer sees fit to maintain testosterone levels at what's necessary to support sperm production. After about a year, a characteristic size and texture change occurs in the testicle, and any qualified vet should be able to recognize the signs of zinc neutering.
I am aware of zinc toxicity and the resulting copper deficiency, and I wish I could say I found it in the course of this research, but I found it on a medical drama about an actor poisoned by denture cream. :-/
As it happens, there was an attempt, (
http://forums.eunuch.org/showthread.php ... =Neutersol) but the original poster deleted most of the post, along with it most of the search keywords I tried. Unfortunately, he seemed to be in the same boat I am - looking for a less-invasive solution for chronic orchialgia than surgical castration.
Please know that if I do go ahead with this, I'll be using fresh, brand-name drug and not homebrew, and under formal medical supervision, with the intent of writing up a case study to be published in whatever journal will have it. Unfortunately, since DonFL deleted his post, I can't try to learn from his mistakes. (After all, in science, even failures are illuminating!)
