I was recently asked about the use of Methotrexate in the horse by an owner. She had obtained some ( your guess is as good as mine where it came from) at the recommendation of her trainer( remember ,this is an injectable prescription drug). She was told that it would help her horse move "smoother". Methotrexate has been used for years in race horses as a supposed treatment for arthritis. This is because it's human use is as a chemotherapeutic agent and has been used to suppress the immune response in rhumatoid arthritis and certain cancers. It's use to "smooth" out the movement of the horse cannot be justified. A recent report stated the following
"Methotrexate is known to have a negative effect on reproduction. In fact, it is coupled with the drug RU-486, the morning-after pill that causes abortion in humans.
When administered as chemotherapy or to treat arthritis, the law requires patients to be informed: "Tell your doctor if you are pregnant or if you intend to have children. There is a good chance that this medicine may cause birth defects if either the male or female is taking it at the time of conception or if it is taken during pregnancy. Methotrexate may cause harm or even death of the fetus. In addition, many cancer medicines may cause sterility, which could be permanent."
Additional concerns about it's use in the horse are the potentially fatal interactions with other drugs commonly used in equine medicine such as Naproxen
Serious toxicity has occurred when NSAIDs have been used concomitantly with methotrexate; use together with extreme caution
as well as the freqently used Ketoprofen and Phenylbutazone
Medications that may interact with ketoprofen include warfarin, phenylbutazone, probenecid, methotrexate, aspirin, and corticosteroids. Notify your veterinarian or pharmacist if the animal receives any medications.
What frustrates me the most is the total amateur pharmacology that takes place in the horse barns ,showgrounds and racetracks. There seems to be no forthought at all as to what these drugs are doing in their horse. If someone says it might give you an edge....then just stick it in your horse. Hopefully sites like this will help spread some knowledge and owners and trainers will learn to just ask someone that knows........a phone call is cheap.