Antiprogestogens or antiprogestins, also known as progesterone antagonists or progesterone blockers, are a class of
drug
A drug is any chemical substance other than a nutrient or an essential dietary ingredient, which, when administered to a living organism, produces a biological effect. Consumption of drugs can be via insufflation (medicine), inhalation, drug i ...
s which prevent
progestogens like
progesterone from mediating their
biological effects in the body. These drugs competitively inhibit progestin at progesterone receptors, acting by
blocking the
progesterone receptor (PR) and/or
inhibiting or
suppressing progestogen
production. Antiprogestogens are one of three types of
sex hormone antagonists, alongside
antiestrogens and
antiandrogens.
Clinical applications
Antiprogestogens are used as
abortifacients,
emergency contraceptives, and in the treatment of
uterine fibroids. They are also being studied in the treatment of
breast cancer. Examples include the
progesterone receptor weak
partial agonist
In pharmacology, partial agonists are drugs that bind to and activate a given Receptor (biochemistry), receptor, but have only partial Intrinsic activity, efficacy at the receptor relative to a full agonist. They may also be considered Ligand (bio ...
mifepristone, the
selective progesterone receptor modulator (SPRM)
ulipristal acetate, and the
silent antagonist aglepristone.
In
medical abortion, mifepristone is combined with a
prostaglandin (e.g.,
gemeprost), while ulipristal is used for emergency contraception.
Development and approval
Several hundred antiprogestogens have been developed, but only three—
mifepristone,
lilopristone, and
onapristone—have been administered to humans. Of these, only mifepristone has been approved and introduced for clinical use.
Role and mechanism of action
Progestins, including progesterone, are vital for preparing the uterus for the implantation of a fertilized egg during the luteal phase of the menstrual cycle. If fertilization, implantation, and other events necessary for pregnancy occur, increased progestin (i.e., progesterone) levels are essential in maintaining the pregnancy. Blocking the effects of progestins like progesterone is associated with anti-gestational effects, resulting in the interruption of pregnancy maintenance.
See also
*
Antiestrogen
*
Antiandrogen
References
External links
*
Antiprogestinentry in the public domain NCI Dictionary of Cancer Terms
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