Medical Abortion Medications
Medical abortion is accomplished using a combination of mifepristone 200 mg orally followed by misoprostol 800 mcg (administered vaginally, buccally, or sublingually) 24-48 hours later, which is safe and highly effective through 63 days of gestation with a success rate of approximately 95-98%. 1, 2, 3
Standard Two-Drug Regimen
The evidence-based protocol consists of:
- Mifepristone 200 mg taken orally first, which blocks progesterone receptors and causes decidual breakdown of the uterine lining 2, 4, 3
- Misoprostol 800 mcg administered 24-48 hours later via vaginal, buccal, or sublingual route 1, 4, 5, 3
Route of Misoprostol Administration
All three routes are highly effective:
- Vaginal administration achieves 93-97.5% complete abortion rates and has been most extensively studied 4, 5, 6
- Buccal administration achieves 95-98% efficacy and is equally effective as vaginal administration, with similar patient satisfaction 5, 3
- Sublingual administration is also effective, though vaginal and buccal routes are more commonly recommended 7
The choice between routes can be based on patient preference, as efficacy is comparable across all three methods 5.
Efficacy by Gestational Age
Success rates vary slightly by gestational age:
- 29-42 days gestation: 98.8% efficacy 3
- Up to 49 days (7 weeks): 97.5-98.5% efficacy 4, 6
- 50-56 days (8 weeks): 95-97% efficacy 5, 3
- 57-63 days (9 weeks): 95.5% efficacy 3
Medical abortion can be performed in outpatient or home settings before 9 weeks of gestation 1, 8
Alternative Regimen: Simultaneous Administration
Mifepristone and misoprostol can be administered simultaneously (rather than 24 hours apart) with comparable efficacy:
- Simultaneous administration: 95.1% complete abortion rate 4
- 24-hour interval: 96.9% complete abortion rate 4
However, simultaneous administration causes more gastrointestinal side effects (nausea, diarrhea, warmth/chills) 4.
Second-Trimester Medical Abortion
For gestations beyond the first trimester:
- Mifepristone 200 mg followed by misoprostol 24-48 hours later is the most effective regimen, achieving 95% completion within 24 hours of misoprostol administration 7
- This combined regimen reduces abortion time by 40-50% compared to misoprostol alone 7
- Misoprostol alone (400-800 mcg every 3-12 hours) achieves 80-85% abortion rates at 24 hours when mifepristone is unavailable 7
Critical Safety Considerations
Absolute Contraindications
Do not use misoprostol in patients with:
- Previous cesarean delivery due to 13% risk of uterine rupture (this applies specifically to labor induction in third trimester, not first-trimester medical abortion where risk profile differs) 8
Essential Preventive Measures
All Rh-negative women must receive:
- Anti-D immunoglobulin 50 mcg within 72 hours (or 300 mcg if lower dose unavailable) to prevent alloimmunization, which occurs in 32% of spontaneous abortions 1, 2, 8
Contraceptive Counseling
- Ovulation can resume within 2-4 weeks post-abortion 1
- Combined hormonal contraceptives or implants can be initiated immediately after complete abortion 1
- No backup contraception needed if started within 7 days of abortion 1
Common Pitfalls to Avoid
Expectant management is absolutely contraindicated in confirmed retained abortion with bleeding, as it carries 60.2% maternal morbidity versus 33.0% with active treatment, including 38% infection rate and 23.1% postpartum hemorrhage rate 1.
Do not delay treatment waiting for fever in suspected infection—maternal tachycardia, purulent cervical discharge, and uterine tenderness warrant immediate broad-spectrum antibiotics and urgent surgical evacuation 1.
Surgical evacuation (dilation and evacuation) becomes the preferred method at gestations ≥16 weeks with confirmed fetal demise 1.