ECP Injection Side Effects in Canines

Veterinarians have used estradiol cypionate (ECP) injections to treat such things as benign anal tumors in elderly male dogs, urinary incontinence in spayed female dogs, and even to prevent the implantation of fertilized ova in cases of mismating (that is, when an inadvertent or unsuitable mating occurs). There are, however, a number of risks and potentially severe side effects associated with this drug. Because of these dangers--as well as the fact that there are now less toxic medications available--few veterinarians even consider using ECP in canines these days.

  1. Cystic Endometrial Hyperplasia and Pyometra

    • Dogs injected with estradiol cypionate to prevent embryo implantation have a high incidence of cystic endometrial hyperplasia and pyometra in response to the hormone. Cystic endometrial hyperplasia is a progressive pathologic change in the uterine lining, which will often thicken and form cysts. Pyometra occurs when the uterus becomes inflamed or infected, filling with fluid and white blood cells. PetEducation.com warns that this is a serious condition and can be life-threatening, particularly if it progresses to a uterine rupture.

    Bone Marrow Suppression

    • A dog's bone marrow is involved in the production of red blood cells that carry oxygen, white blood cells that fight infection, and platelets that help control bleeding and bruising. Estrogens, however, are considered toxic to the bone marrow of small animals. Because ECP is a semisynthetic estrogenic hormone, it can cause the suppression of bone marrow function in a dog, leading to blood abnormalities and the increased risk of anemia, fatigue, infection, and bleeding and bruising.

    Signs of Estrus

    • After an injection of ECP, your dog might show continued signs of estrus. Symptoms such as a swollen or wrinkled vulva, attention from and toward male dogs, and blood-tinged vaginal discharge can occur. Keep in mind, however, that pyometra also causes vaginal discharge, although usually with little or no blood. Because pyometra can be fatal, if you notice any indication of vaginal discharge in your dog, contact your veterinarian.

    Feminization Syndrome

    • If a male dog is given an injection of ECP, the hormone might cause him to experience feminization syndrome. This is a condition in which the male dog takes on uncharacteristic female qualities. His penis may shrivel or shrink, his breasts may enlarge, and he may adopt a female position when he urinates.