MIFEPREX
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MIFEPREX (MIFEPREX).
Mifepristone is a synthetic steroid with potent antiprogestin activity via competitive antagonism of progesterone at progesterone receptors, leading to decidual necrosis and cervical softening. It also has weak antiglucocorticoid activity.
| Metabolism | Primarily metabolized by CYP3A4 isoenzymes; minor pathways via CYP2C19 and CYP2B6; undergoes rapid first-pass metabolism to active metabolites (e.g., monodemethyl-mifepristone). |
| Excretion | Primarily fecal (83%) via bile; renal excretion accounts for approximately 9% as metabolites. Unchanged drug in urine is minimal. |
| Half-life | Terminal elimination half-life ranges from 18 to 30 hours (mean 24 hours). In patients with hepatic impairment, half-life may be prolonged up to 60 hours. |
| Protein binding | High (98–99%) bound to alpha-1-acid glycoprotein and albumin. |
| Volume of Distribution | Apparent volume of distribution is approximately 0.5–1.2 L/kg (mean 0.8 L/kg), indicating distribution into total body water. |
| Bioavailability | Oral bioavailability is approximately 69% (range 40–80%) due to extensive first-pass metabolism; interindividual variability is high. |
| Onset of Action | Oral: Onset of action occurs within 4–6 hours for uterine contractions and cervical softening; peak effect at 24–36 hours. |
| Duration of Action | Duration of action for pregnancy termination is 24–48 hours; some effects (e.g., cervical softening) persist up to 72 hours. Uterine activity may last for several days post-administration. |
Oral administration: 600 mg single dose on day 1, followed by oral misoprostol 400 mcg 48 hours later.
| Dosage form | TABLET |
| Renal impairment | No dose adjustment required for renal impairment; insufficient data for GFR <15 mL/min. |
| Liver impairment | Contraindicated in severe hepatic impairment (Child-Pugh class C). Use with caution in Child-Pugh class A or B; no specific dose adjustment recommended. |
| Pediatric use | Safety and efficacy not established in pediatric patients; use not recommended. |
| Geriatric use | No specific dose adjustment required; use caution due to potential comorbidities and polypharmacy. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for MIFEPREX (MIFEPREX).
| Breastfeeding | Mifepristone is excreted into breast milk; M/P ratio is approximately 0.5. After a single dose, milk levels are low, but accumulation with repeated doses may occur. Caution is advised; pump and discard milk for 3-5 days after administration to minimize infant exposure. |
| Teratogenic Risk | First trimester: Mifepristone is contraindicated for pregnancy continuation due to high risk of abortion and potential teratogenicity. Fetal exposure can result in incomplete abortion, hemorrhage, and fetal anomalies including limb defects, cranial nerve agenesis, and cardiac malformations. Second and third trimesters: Risk of preterm labor, fetal distress, and maternal hemorrhage. Use only for induction of abortion or labor in indicated settings. |
■ FDA Black Box Warning
Mifeprex must be prescribed and administered by a qualified healthcare provider who can assess ectopic pregnancy risk, provide emergency contraception, and manage incomplete abortion or severe bleeding. Patients must be informed of the risk of serious bacterial infection and sepsis. Strict adherence to dosing regimen required; uterotonic agents (e.g., misoprostol) are mandatory for efficacy.
| Serious Effects |
Confirmed or suspected ectopic pregnancy; chronic adrenal failure; concurrent long-term corticosteroid therapy; hemorrhagic disorders or anticoagulant use; inherited porphyria; hypersensitivity to mifepristone or misoprostol; IUD in place (must remove prior to treatment).
| Precautions | Risk of serious bacterial infection and sepsis (including fatal cases) following abortion; hemorrhage requiring surgical intervention; incomplete abortion requiring suction aspiration; ectopic pregnancy (must be excluded prior to use); rare cardiovascular events with concomitant CYP3A4 inhibitors. |
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| Fetal Monitoring | Monitor for heavy bleeding, incomplete abortion, infection, and uterine rupture. Obtain baseline hemoglobin/hematocrit; repeat if bleeding suspected. Ultrasound confirmation of complete abortion required. Monitor vital signs and pain level. In emergency settings, assess for need for surgical evacuation. |
| Fertility Effects | Mifepristone is a progesterone receptor antagonist; can impair ovulation and endometrial preparation. Post-treatment, fertility typically returns to baseline after a normal menstrual cycle. No evidence of permanent infertility. |