Mifepristone

Mifepristone is a prescription drug used to terminate pregnancies. It belongs to a family of fertility control agents called antiprogesterones. These drugs are steroids that inhibit the action of progesterone. Mifepristone was developed and first marketed in France. The Food and Drug Administration approved the use of mifepristone in September 2000 amid controversy.

Other Names

Mifepristone is commonly called RU-486, which was the name of the drug as it was being developed by Roussel Uclaf company. It is marketed by Danco Labs under the name Mifeprex in the United States, and by Xelgyn Laboratories under the name Mifegyne in other countries.

Uses

Mifepristone is an abortificient used to terminate pregnancies through the 49th day after the first day of a woman's last menstrual period. In Sweden and the United Kingdom, mifepristone can be used through the 63rd day of pregnancy.

Mifepristone can be used in combination with gemeprost to terminate a pregnancy between the 13th and 24th week of gestation.

How Mifepristone is Taken

Mifepristone is sold in 200-mg tablets. To terminate a pregnancy 600 mg mifepristone is taken at one time. If a complete abortion has not occurred after three days, misoprostol (Cytotec) is taken and the effectiveness of the treatments is determined 11 days later.

How Mifepristone Works

Maintenance of a pregnancy is dependent on the hormone progesterone. Mifepristone is works as an antiprogesterone agent by binding to the progesterone receptor. However, mifepristone does not activate the receptor, but rather blocks progesterone from binding. Without the supportive influence of progesterone, the cervix dilates and softens, the placenta detaches from the uterine wall, and the uterus contracts. All these effects result in termination of a pregnancy.

How the Body Affects Mifepristone

Mifepristone is rapidly absorbed, with peak circulating levels occurring approximately 90 minutes after ingestion. The half-life of mifepristone, or time needed for the concentration of the drug in the blood to be reduced by half, is approximately 18 hours. Mifepristone is primarily metabolized in the liver by the enzyme CYP3A4. Most of mifepristone is excreted in the feces (approximately 83%).

Side Effects

Studies show that 80%–90% of women experience heavy bleeding after taking mifepristone. Other common side effects include the following:

• abdominal pain
• uterine cramping
• nausea
• vomiting
• diarrhea

Pelvic pain, fainting, headache, dizziness, and feeling of weakness are rare side effects.

Risks and Precautions

Prolonged heavy vaginal bleeding after taking mifepristone is NOT proof of a complete abortion since this can occur even if the abortion attempt is unsuccessful. If the treatment does fail, there is a risk of birth defects. Abortion by surgery may be necessary in these cases.

Mifepristone is NOT used in the following circumstances:

• Ectopic pregnancy
• Intrauterine device (IUD) in place
• Chronic adrenal failure
• Concurrent long-term corticosteroid therapy
• History of allergic reactions to mifepristone, misoprostol or other prostaglandins
• Bleeding disorders or concurrent anticoagulant therapy
• Inherited porphyrias (a group of blood disorders)

Drug Interactions

Drugs that inhibit CYP3A4 could elevate blood levels of mifepristone. Some potent CYP3A4 inhibitors include ketoconazole (Nizoral), itraconazole (Sporanox), erythromycin, and components of grapefruit juice. Drugs that increase CYP3A4, called CYP3A4 inducers, can lower blood levels of mifepristone. Some CYP3A4 inducers include rifampin (Rifadin, Rimactane), dexamethasone, St. Johns Wort, phenytoin (Dilantin), and carbamazepine (Tegretol).

Controversy

Many pro-life groups all over the world have protested the approval and use of mifepristone. Some groups believe that, in addition to its effects on pregnancy, mifepristone use is harmful to many women. In the United States, a citizen’s petition called RU-486 Suspension and Review Act, or Holly’s Law, called for the ban of mifepristone based on the risk to the mother. The law was initiated by the parents of Holly Patterson, an 18-year-old who died after taking mifepristone with misoprostol. She was the third woman to have died after mifepristone use.

Research

A Trial of 2,121 women in the United States showed that mifepristone caused a complete abortion one not requiring surgery) in 92% of women.^[1] However, only 6% of the women had a complete abortion within 2 days of taking mifepristone by itself. Most of the women in the study needed to follow up with misoprostol. Misoprostol follow-up caused a complete abortion in 63% of the women within 24 hours of treatment. Surgical abortion was needed in 8% of women.

References

1. ↑ Spitz IM, Bardin CW, Benton L, Robbins A. Early pregnancy termination with mifepristone and misoprostol in the United States. N Engl J Med. 1998 Apr 30;338(18):1241-7. Abstract | Full Text | PDF

External Links

FDA: Patient Information Sheet