Alternative Name: ZK 98.299; ZK 98 299

Description: A study in bonnet monkeys found that low-dose onapristone treatment prevented pregnancy without disturbing the menstrual cycle and ovulation in the majority of cycles. Anovulation and luteal insufficiency occured in some animals during prolonged treatment. Given the resulting inhibition of endometrial receptivity, onapristone was studied as an antiprogestin for endometrial contraception.

Product Details

Dose: 2.5 or 5 mg

Active Pharmaceutical Ingredient (API):

Inactive material: benzyl benzoate; castor oil

Status Details

Began discovery in: Prior to 1993

Status Details:
  • Development for contraceptive indication was discontinued in early 2000s. Onapristone was in Phase II trials for prostate cancer and is now in clinical trials for the treatment of breast cancer.

Additional Information

  • Puri CP, et al. (2000) Endometrial contraception: modulation of molecular determinants of uterine receptivity. Steroids. 65(10-11):783-94.

  • Katkam RR, et al. (1995) Onapristone (ZK 98.299): a potential antiprogestin for endometrial contraception. Am J Obstet Gynecol. 173(3 Pt 1):779-87.

  • Schering AG is now part of Bayer HealthCare Pharmaceuticals. Arno Therapeutics previously had the rights to Onapristone; Context Therapeutics currently has them.

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