Mifegyne (Mifepristone)

Mifepristone acts on progesterone‑dependent pathways to achieve therapeutic outcomes in the following conditions:

• Medical termination of intrauterine pregnancy (≤10 weeks gestation): induces uterine expulsion of the gestational sac when used with a prostaglandin analogue.
• Cushing's syndrome (off‑label): blocks glucocorticoid receptors to reduce cortisol‑mediated effects in selected patients.

• Mifepristone binds competitively to progesterone receptors in the uterus, preventing progesterone‑mediated maintenance of the endometrium, leading to decidual breakdown and detachment of the gestational sac. It also exhibits antagonism at glucocorticoid receptors, diminishing cortisol signaling, which underlies its off‑label use in Cushing’s syndrome. The receptor blockade disrupts luteal phase support, sensitizes the myometrium to prostaglandins, and promotes cervical softening, facilitating expulsion of pregnancy tissue.

Mifepristone may cause a range of adverse reactions, which are grouped by frequency.

Common Side Effects

• Nausea: mild to moderate upset stomach.
• Vomiting: occasional emesis after dosing.
• Abdominal pain: cramping or discomfort in the lower abdomen.
• Vaginal bleeding: spotting or heavier flow during the abortion process.
• Diarrhea: loose stools occurring within days of administration.
• Fatigue: transient tiredness or weakness.

Serious or Rare Side Effects

• Heavy bleeding: excessive hemorrhage requiring medical attention.
• Infection: signs of uterine or systemic infection such as fever.
• Incomplete abortion: retained tissue necessitating further intervention.
• Allergic reaction: rash, itching, or anaphylaxis in rare cases.
• Liver enzyme elevation: abnormal hepatic function tests observed in isolated reports.

Before prescribing Mifegyne, clinicians should consider several safety measures:

• Assess gestational age: confirm pregnancy is ≤10 weeks.
• Confirm contraindications: exclude ectopic pregnancy, chronic adrenal insufficiency, or severe bleeding disorders.
• Obtain informed consent: discuss expected outcomes and potential risks with the patient.
• Monitor vital signs: watch for signs of hemorrhage or hemodynamic instability after dosing.
• Avoid concomitant CYP3A4 inducers: drugs like rifampin may reduce efficacy.
• Store at ambient temperature: keep in the original pack, protect from moisture and light.

Mifepristone can interact with other medicines, altering its effectiveness or safety profile.

Major Interactions (Avoid)

• Rifampin: strong CYP3A4 inducer that markedly lowers plasma concentrations of mifepristone.
• Carbamazepine: enzyme inducer that may reduce therapeutic levels and compromise efficacy.

Moderate Interactions (Monitor Closely)

• Azole antifungals (e.g., ketoconazole, fluconazole): CYP3A4 inhibitors that can increase mifepristone exposure.
• SSRIs: may enhance bleeding risk when combined with prostaglandin agents used in the regimen.
• Hormonal contraceptives: could diminish the effectiveness of the mifepristone‑misoprostol protocol.