Osaterone acetate

2-oxachloromadinone acetate • Ypozane

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  • Osaterone acetate.

Class of drug

  • Steroidal androgen antagonist.



  • Osaterone is a derivative of chlormadinone acetate and is a steroid chemically related to progesterone. It is a potent progestagen and a potent anti-androgen and also has some glucocorticoid effects.
  • Both osaterone and its major metabolite (15²-hydroxylated osaterone acetate) are pharmacologically active.
  • Osaterone acetate competitively prevents the binding of androgens to their prostatic receptors and blocks the transport of testosterone into the prostate. The effects are dose-dependent.


  • For the treatment of benign prostatic hypertrophy (BPH ) in male dogs.
    • BPH is an increase in size or non-malignant hypertrophy of the prostate and is the most common disease of the prostate in entire male dogs.
    • The increase in prostate size is caused by changes in the ratio of androgens, like testosterone and estrogens.
    • Many dogs are asymptomatic but clinical signs can result when there is a large degree of prostate hyperplasia.
    • Treatment aims to decrease the size of the prostate gland and thus alleviate clinical signs (such as constipation and difficulty in urinating).

Adverse reactions

Effects of overdosage

  • At dose rates <10 mg/kg bodyweight:
    • Reduced food intake.
    • Reduced bodyweight gain
  • At dose rates >10 mg/kg:
    • Ataxia and tremors

Other reported reactions

  • Mainly associated with progestational effects of osaterone acetate:
  • A transient increase in appetite occurs very commonly.
  • Transient behavioral changes such as increased or decreased activity, or more sociable behavior, are common.
  • Other adverse reactions, including transient vomiting and/or diarrhea, polyuria/polydipsia, lethargy or feminization syndrome including mammary gland hyperplasia occur uncommonly.
  • A transient reduction in plasma cortisol occurs in most treated animals.
  • Treatment does not usually need to be discontinued. In clinical trials, all dogs recovered without any specific therapy.
  • Mammary gland hyperplasia was seen as a very rare adverse effect of osaterone during a laboratory study.
  • NOEL for mammary gland proliferation of 100 mg/kg/day was calculated for male dogs (in female dogs this is 0.1 mg/kg/day (1 month)).
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