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1466 Onapristone
37aec088648ee08c096d5375c66fa967287481433431c04d08f08ad3c11c47fa

Properties

Background

Yellow
Bottle

Purple
Cap

Light green
Syringe

Yellow
Bubbles
No
Drops
Yes
Label
Leaf

Chemistry

Formula
C29H39NO3
Carbon
29
Polarity
Neutral

Onapristone (developmental code names ZK-89299, ZK-299) is a synthetic and steroidal antiprogestogen with additional antiglucocorticoid activity which was developed by Schering and described in 1984 but was never marketed. It is a silent antagonist of the progesterone receptor (PR), in contrast to the related antiprogestogen mifepristone (which is a weak partial agonist of the receptor). Moreover, compared to mifepristone, onapristone has reduced antiglucocorticoid activity, shows little antiandrogenic activity, and has 10- to 30-fold greater potency as an antiprogestogen. The medication was under development for clinical use, for instance in the treatment of breast cancer and as an endometrial contraceptive, but was discontinued during phase III clinical trials in 1995 due to findings that liver function abnormalities developed in a majority patients.

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