Estradiol

Major Uses

Estradiol is a semi-synthetic estrogen (estradiol cypionate) used to increase levels of estrogen in the body. It is generally used as a replacement therapy, but may also be administered to prevent embryo implantation in dogs and cats. Other uses of the drug include palliative treatment for benign anal tumors, treatment of urinary incontinence, and treatment of anestrus.

Estradiol is not approved by the Food and Drug Administration for use in cats and dogs, but it is prescribed legally as an extra-label drug by veterinarians.

Common Precautions

Vomiting, loss of appetite, bone marrow suppression, lethargy, vaginal discharge, diarrhea, pyometra, aplastic anemia, bleeding, and death are possible side effects of estradiol use. When used to prevent embryo implantation, estradiol is associated with a high incidence of pyometra and cystic endometrial hyperplasia.

Use of estradiol in males can cause feminization. It should not be administered to breeding males. In small animals, estradiol and other estrogens are toxic to bone marrow and may cause blood dyscrasias. Animals with cancers related to or caused by estrogen, such as mammary cancer, and those with bone marrow disease should not be given this medication. This drug can cause birth defects or abortion if administered to pregnant animals. Estradiol is not safe for use in lactating animals.

This drug may interact with other medications and supplements, including tricyclic antidepressants, corticosteroids, barbiturates, ketoconazole and macrolide antibiotics, hydantoin, anticoagulants, and others.

Estradiol should not be used in animals with a known allergy or hypersensitivity to the drug. Estradiol overdose can cause anemia and thrombocytopenia. In some cases, ingestion of very high doses of estradiol may cause liver, heart, and pancreas damage. Any known or suspected overdose should be reported to a veterinarian right away.

Storage

Estradiol should be stored in a light resistant, tight fitting container at room temperature. It should be kept well out of the reach of children and animals and should not be exposed to freezing temperatures.

Administration

Estradiol is available as tablets and in an injectable form. The generally recommended dose for mismating in dogs is 0.01 to 0.02 mg per pound (0.02 - 0.04 mg/kg) given intramuscularly. For cats, the dose for mismating is 0.0625 to 0.125 mg per pound (0.125-0.25 mg/kg) intramuscularly. Doses may vary in different species, when the drug is given by a different route or concurrently with other medications, and with regards to a patient's age, breed, and health status. A veterinarian's dosing instructions and/or those printed on the medication label should be followed closely.

If a single dose of estradiol is missed, it should be taken as soon as possible. If it is almost time for the next dose, the missed dose should be skipped and a normal schedule should be resumed. Two doses should not be given at the same time.