Interferon Therapy for MPNs in Canada in 2025: Shortages, Stopgaps, and Why BESREMi Matters for PV

Interferons have long been part of the therapeutic backbone for Philadelphia–chromosome–negative myeloproliferative neoplasms (MPNs)—especially polycythemia vera (PV)—because they control blood counts and, uniquely, can drive down the JAK2 V617F mutation burden over time (a potential marker of disease modification). Contemporary reviews and guidelines continue to position pegylated interferon-α alongside hydroxyurea as a first-line cytoreductive option in PV, particularly for younger patients and those aiming to avoid or come off hydroxyurea.

The Canadian context: what’s been used—and what’s missing

Historically in Canada, peginterferon alfa-2a (PEGASYS)—authorized for hepatitis B/C—has been prescribed off-label for PV and related MPNs. Other interferon products have dwindled: interferon alfa-2b (Intron A) has been discontinued in Canada (and abroad), leaving peginterferon alfa-2a as the practical interferon option for many hematologists.

The shortage: a Tier 3 supply crunch

Canada entered a Tier 3 (most serious) shortage of PEGASYS beginning October 29, 2024, with the shortage listed as ongoing through December 31, 2025. The Drug Shortages Canada database and Health Canada’s InfoWatch both flagged this as critical, noting real risks for MPN patients who depend on interferon therapy—even though PEGASYS is not formally authorized for MPNs.

To mitigate the impact, Health Canada (March 17, 2025) permitted the exceptional, temporary importation of US-authorized BESREMi (ropeginterferon alfa-2b-njft). Crucially, Health Canada emphasizes that BESREMi is “similar but not identical” to PEGASYS; it carries different dosing, indication, and monitoring requirements and should not be considered a direct substitute. It also lacks a Canadian DIN and may not appear in standard pharmacy systems, requiring special billing processes.

Recalls and Safety Alerts

Professional bodies and pharmacy groups circulated practical guidance on converting appropriate patients, while also clarifying important exceptions (e.g., pregnant patients and those with CTCL should generally remain on PEGASYS when possible).

Following Health Canada’s temporary pathway, distributor FORUS Therapeutics announced US-authorized BESREMi is available in Canada via Exceptional Importation, with technical details (e.g., Ontario PIN 09858357 and Quebec RAMQ code 99114432) to enable billing/logistics.

BESREMi remains not yet reviewed under Health Canada’s standard drug review process in 2025, but a licensing/registration track with the originator company (PharmaEssentia) is underway.

What makes interferon—and BESREMi—important for PV?

Disease control that can be “disease-modifying.”

Randomized and long-term extension studies demonstrate that ropeginterferon alfa-2b (BESREMi) achieves durable complete hematologic responses and deep molecular responses (reductions in JAK2 V617F allele burden), with outcomes that strengthen over time. The PROUD-PV trial and CONTINUATION-PV extension (to 5–6 years) showed sustained efficacy and, in later follow-up, signals such as improved event-free survival compared with control arms. PMCNature

Emerging analyses (and real-world/clinical experience reports) continue to link deeper JAK2 burden reductions with favourable clinical trajectories, underscoring why many clinicians view interferon as the only cytoreductive option with robust, prospective molecular-response data in PV.

Tolerability and cadence.

Ropeginterferon’s long half-life enables dosing every 2–4 weeks (after titration), which many patients find easier than weekly regimens associated with older interferons. Several reviews highlight comparatively lower long-term discontinuation rates with ropeginterferon versus historical interferon formulations in PV cohorts.

A viable first-line option—especially for younger PV patients.

Reviews and expert algorithms place pegylated interferon-α alongside hydroxyurea as first-line cytoreduction in PV. For younger patients who may be on therapy for decades, the potential for sustained hematologic control and molecular remissions makes interferon particularly attractive.

Practical implications of the PEGASYS shortage

Who should switch?

Canadian hematology groups and pharmacy bodies recommend considering BESREMi for appropriate patients affected by the shortage, while noting specific groups should not be switched (e.g., pregnancy and CTCL, where PEGASYS remains preferred). The decision belongs to the treating hematologist, who will individualize based on prior response, comorbidities, and goals (e.g., fertility, molecular response).

Dosing and monitoring are not interchangeable.

Health Canada’s risk communication stresses that BESREMi has different dosing and monitoring than PEGASYS; clinicians are directed to the US Prescribing Information and relevant guidelines, and patients require counseling on syringe format and handling (BESREMi arrives as a single-use prefilled syringe with English-only labels).

Coverage and logistics

Because BESREMi’s importation is exceptional (without a DIN), ordering and billing require special processes and may vary by province/plan. FORUS has published provincial billing identifiers to facilitate dispensing; patients and providers should work with specialty pharmacies and insurers on case-by-case arrangements.

How BESREMi changes the near-term landscape for Canadian PV patients

While Canada addresses the PEGASYS shortage through at least December 2025, the availability of BESREMi offers a credible, evidence-based interferon path for many PV patients who otherwise faced therapy disruption or suboptimal alternatives. It is particularly impactful for patients aiming for long-term disease control with potential molecular remissions, for those intolerant or resistant to hydroxyurea, and for clinicians striving to reduce phlebotomy burden while adhering to hematocrit and thrombotic-risk targets.

That said, not every patient should be switched, and interferon choice in pregnancy remains a special case (PEGASYS preferred when feasible). The message from Canadian advisories is consistent: coordinate closely with your hematology team to determine suitability, dosing, and monitoring—and to navigate the temporary logistics of an imported product.

Bottom line

Interferon remains a cornerstone for PV in Canada, valued for durable hematologic control and the unique potential to reduce JAK2 V617F allele burden over time. Wiley Online Library

Canada is experiencing a Tier 3 PEGASYS shortage (Oct 2024 → Dec 2025), officially recognized by Health Canada.

In response, US-authorized BESREMi is temporarily available through exceptional importation, with distinct dosing/monitoring and special handling (no DIN).

Why it matters for PV: BESREMi brings long-term, disease-modifying potential with convenient dosing and robust trial data—helping preserve interferon access during the shortage and potentially improving long-run outcomes for many Canadian PV patients.

Switching from PEGASYS® to BESREMI®: What Patients Should Ask

Ask About Your Suitability

Am I a good candidate for BESREMi®?

• Are there reasons I should stay on PEGASYS®, such as pregnancy or other conditions?

• How will switching impact my treatment goals, such as controlling hematocrit or reducing my JAK2 mutation burden?

Know the Side Effects

What side effects should I expect with BESREMi®?

• How do I report side effects or concerns early?

• What should I do if I miss a dose?

Understand the Differences

How is the dose and schedule different from PEGASYS®?

• What new monitoring (labs, visits) will I need?

• Will I be able to self-inject, and how often

Learn About Logistics

Which pharmacy will dispense BESREMi®?

• How is the medication stored and handled?

• How is insurance coverage or reimbursement arranged, and who can help with paperwork?

Plan for Follow-Up

How often will we check my blood counts and liver function after the switch?

• How will we measure whether the medication is working for me?

• What are the steps if BESREMi® isn’t effective or tolerated?