Why Are Pregnancy Tests Required for ERA Medications?

For people who can become pregnant (females of reproductive potential) taking an Endothelin Receptor Antagonist (ERA)—such as macitentan, ambrisentan, or bosentan—for pulmonary arterial hypertension (PAH), the FDA requires strict participation in a safety program ^[1][2]. This program involves mandatory pregnancy testing before, during, and after treatment to receive your medication. This requirement is in place because ERAs carry a severe risk of causing birth defects (teratogenicity) if taken during pregnancy ^[3][4]. To prevent any accidental exposure to a developing fetus, the FDA manages these therapies through a Risk Evaluation and Mitigation Strategy (REMS) program ^[1].

Urgent Safety Note: Do not run out of or abruptly change your PAH treatment on your own. If you have a positive pregnancy test, miss your period, or suspect your birth control has failed, contact your PAH prescriber immediately. Both a potential pregnancy and an unsupervised interruption of your PAH medication require urgent specialist attention.

The Risks to Fetal Development

Endothelin-1 is a potent substance in the body that constricts blood vessels. ERAs work by blocking its receptors, which helps relax the blood vessels in your lungs and lower the dangerous pressure caused by PAH. However, endothelin signaling is also important for normal fetal development ^[5].

Research supporting these safety rules includes:

• Animal Studies: In animal testing, ERAs have caused severe developmental issues, particularly craniofacial malformations (abnormalities of the head and face) ^[3][4].
• Cardiopulmonary Development: Endothelin plays a role in the heart and lung development of the fetus, so blocking it may disrupt how the fetal cardiovascular system adapts ^[5].
• Placental Transfer: Laboratory studies using human placentas have shown that ERAs like ambrisentan and macitentan can cross into the fetal compartment ^[6].

While human pregnancy data is limited, the severe risks seen in animal and laboratory studies mean that all three ERA medications—macitentan, ambrisentan, and bosentan—are strictly contraindicated during pregnancy ^[2][3]. Additionally, pregnancy itself is considered a high-risk medical state for anyone with PAH, making pregnancy prevention doubly important for your own health.

Understanding the FDA REMS Requirements

The REMS program ensures that prescribers, pharmacies, and patients all follow specific safety protocols to prevent fetal exposure ^[1]. While the exact rules can vary slightly depending on your specific medication and the pharmacy dispensing it, the REMS generally requires:

• Baseline Testing: A negative pregnancy test before you are permitted to start the medication ^[1].
• Monthly Testing: A negative pregnancy test every single month before the specialty pharmacy can release your next refill ^[1]. Home testing is sometimes accepted, but you must confirm this with your specific pharmacy and REMS program rules.
• Post-Treatment Testing: Because the medication stays in your system, a final pregnancy test is typically required one month after you take your last dose of the ERA.
• Strict Contraception: You must use highly reliable birth control during treatment and for one month after your final dose. The program often requires one highly effective method (like an IUD) or a combination of two methods (like the pill plus condoms). Important Note: Unlike macitentan ^[7], bosentan can reduce the effectiveness of some hormonal contraceptives. You must verify with your prescriber which contraceptive methods and combinations are acceptable and safe for your specific ERA ^[2].

Managing the Program Requirements

Navigating REMS requirements can feel invasive, and patients and caregivers often find the logistics challenging ^[8][9]. If a test is missed or delayed, the pharmacy cannot dispense your medication, which can lead to a dangerous gap in your treatment.

Action Plan for Testing and Delays:

• Set Reminders: Schedule a monthly alarm to complete your test and report it to the specialty pharmacy with enough time before your refill is due.
• Travel Planning: If you will be traveling or have difficulty accessing a lab, contact your specialty pharmacy early to arrange testing and prevent medication delays.
• Contraceptive Failure or Missed Period: If your birth control fails, you miss a period, or a test turns up positive, do not wait for your next appointment. Contact your PAH care team immediately for urgent, specialized medical guidance so they can safely manage both your PAH and the potential pregnancy exposure.