Osaterone acetate

Osaterone acetate (brand name Ypozane; former developmental code name TZP-4238), also known as 17α-acetoxy-6-chloro-2-oxa-6-dehydroprogesterone, as well as 2-oxachloromadinone acetate, is a steroidal antiandrogen and progestogen used in veterinary medicine in Europe in the treatment of benign prostatic hyperplasia (BPH) in dogs. It was also investigated in Japan in the treatment of prostate cancer and BPH in humans but was never marketed for these indications. Osaterone acetate produces remission of clinical symptoms of BPH in ~83% of dogs for six months after a single one-week course of treatment, and can be used long-term. It is a 17α-hydroxyprogesterone derivative and a derivative of the less potent chlormadinone acetate. The drug is the C17α acetate ester of osaterone.

Osaterone acetate has virtually no estrogenic or androgenic activity. However, it can decrease cortisol levels, interfere with adrenocorticotropic hormone response, induce or exacerbate adrenal insufficiency, and exacerbate diabetes mellitus, side effects indicative that it possesses clinically relevant glucocorticoid properties. Other side effects of osaterone acetate include diminished sperm quality (for up to 6 weeks post-treatment), transient elevation of liver enzymes (caution should be observed with known liver disease), vomiting, diarrhea, polyuria/polydipsia, lethargy, and hyperplasia of the mammary glands. The drug has a long half-life of 197 ± 109 hours in dogs.