A Swedish pharmaceutical company recently announced that the U.S. Food and Drug Administration (FDA) has conditionally approved a new chemotherapeutic drug that will provide veterinary oncologists with a new treatment option in the battle with canine mammary carcinoma and squamous cell carcinoma.
Paccal Vet-CA1 is the first veterinary drug to utilize paclitaxel, which has been a key part of chemotherapy in people for almost two decades. Unfortunately, paclitaxel has been unavailable to dogs because they have an extreme sensitivity to the chemicals required to get the drug into solution.
That requires a little explanation – remember back to chemistry class, where we learned that some things can be dissolved in water (like sugar) and some things can’t (like sand). When injecting a drug into the blood stream, it has to be dissolved in water. There are tricks to get insoluble things dissolved in water, and the trick previously used for paclitaxel is called surfactants. Unfortunately, these are tolerated well enough by humans, but dogs just can’t handle them.
Essentially, when exposed to surfactants, dogs have body-wide allergic reaction and can easily die. Although we are so similar in many ways, there are some very real and scary biological differences between dogs and people, and this is one of them. The new, conditionally-approved drug gets around this problem by using a specially formulated derivative of Vitamin A to allow the drug to be mixed into water-based solutions. In early tests, it seems that dogs can tolerate this method fairly well.
Paclitaxel is a type of drug called a mitotic inhibitor. It stops cells from dividing, and since cancer cells are (almost by definition) cells that are dividing out of control, this has proven to be a very effective way to stop cancer growth. Other cells divide frequently as well, like cells in bone marrow that generate white blood cells and cells that line the intestines. Paclitaxel will also stop those cells from dividing. This explains the most frequent side effects observed with the drug – low white blood cell counts and gastrointestinal problems. The drug, made by the Swedish company Oasmia and distributed by Abbott Animal Health, is “conditionally approved” by the FDA, which means there are some restrictions on its use by veterinary oncologists.
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