What is the recommended dose of methotrexate (MTX) for a medical abortion?

Methotrexate Dosing for Medical Abortion

The standard recommended dose of methotrexate for medical abortion is 50 mg/m² administered intramuscularly, as recommended by clinical guidelines. 1

Dosing Regimen and Administration

• The standard single-dose regimen uses 50 mg/m² of methotrexate administered intramuscularly 1
• This is typically followed by misoprostol 800 mcg administered vaginally 5-7 days later 2
• A multiple-dose regimen may be considered for cases with higher β-hCG levels, as it has a higher success rate (92.7% vs 88.1% for single-dose) 1

Efficacy Considerations

• Success rates with the standard 50 mg/m² dose are approximately:
  • 96% overall success rate in early studies 2
  • 87.7% success rate in multicenter trials 3
  • Higher efficacy (90.6%) at ≤49 days gestation compared to 50-56 days gestation (81.6%) 3

Alternative Dosing Options

Research has explored alternative dosing strategies:

• A fixed 75 mg intramuscular dose has shown comparable efficacy (94.9% success rate) to the 50 mg/m² dosing 4
• A lower 25 mg oral dose followed by misoprostol has demonstrated similar efficacy to 50 mg oral dosing (91% vs 90%) 5, though oral administration is less common in clinical practice

Important Patient Selection Criteria

• Optimal candidates have:
  • Adnexal mass ≤3.5 cm in diameter
  • Gestational age ≤8 weeks (efficacy decreases with advancing gestational age)
  • β-hCG levels <5000 mIU/mL (levels >5000 mIU/mL are generally contraindicated due to reduced efficacy) 1

Contraindications

• Known hypersensitivity to methotrexate
• Active liver disease
• Blood dyscrasias
• Immunodeficiency syndromes
• Alcoholism
• Breastfeeding mothers
• Inability to comply with follow-up requirements 1

Monitoring and Follow-up

• Weekly β-hCG measurements until levels become undetectable (<2 IU/L)
• A decrease in β-hCG from day 1 to day 4 predicts successful treatment
• Patients must avoid pregnancy for at least 3 months after methotrexate treatment due to teratogenic risk 1

Common Pitfalls to Avoid

1. Failing to screen for contraindications: Always check for liver disease, blood dyscrasias, and other contraindications before administering methotrexate
2. Inadequate follow-up planning: Ensure patient can comply with required monitoring
3. Medication interactions: Advise patients to avoid folic acid supplements, NSAIDs, and aspirin during treatment 1
4. Missing signs of complications: Monitor for severe abdominal pain, heavy vaginal bleeding, dizziness, or fever which may indicate serious complications 1

The evidence consistently supports the 50 mg/m² intramuscular dose as the standard for methotrexate in medical abortion, with timing of follow-up misoprostol administration and monitoring protocols being critical to treatment success.