Introduction

Managing voxelotor in sickle cell disease treatment has provided significant clinical insights through real-world registry data. Although the drug was recently withdrawn from global markets, understanding its impact on hemoglobin levels and hemolytic markers remains essential for hematologists. Two major US-based registries, RETRO and PROSPECT, recently published their findings on the safety and effectiveness of this therapy in clinical practice.

Study Methodology and Patient Profiles

The RETRO study focused on retrospective data from 216 participants aged 12 years and older across nine US sites. In contrast, the PROSPECT study involved a larger cohort of 265 participants, including children as young as four years old. This second study utilized both retrospective and prospective data collection methods. Interestingly, both registries monitored patients for approximately one year before they began treatment. The treatment duration varied significantly between the groups, with RETRO participants averaging about 50 weeks and PROSPECT participants exceeding 143 weeks on the medication.

Clinical Benefits of Voxelotor in Sickle Cell Disease

The primary outcomes focused on laboratory improvements and clinical complications. Specifically, researchers observed a consistent increase in hemoglobin levels across both cohorts. In the RETRO group, mean hemoglobin increased by up to 0.8 g/dL over one year. Similarly, the PROSPECT group showed an increase of 0.7 g/dL at the 54-month mark. Furthermore, markers of hemolysis, such as reticulocyte counts and bilirubin levels, showed marked decreases. These improvements suggest that the medication effectively reduced red blood cell destruction in many patients. Additionally, the annualized incidence rates of acute pain crises remained stable in RETRO and actually decreased in the PROSPECT cohort during the follow-up period.

Regulatory Context and Current Status

Despite the favorable laboratory results seen in these registries, Voxelotor was withdrawn from global markets in September 2024. The manufacturer made this voluntary decision after reviewing separate clinical data that suggested an unfavorable risk-benefit profile. Specifically, concerns arose regarding an imbalance in vaso-occlusive crises and fatal events in other trials. Nevertheless, the RETRO and PROSPECT data highlight that, in specific real-world settings, the drug successfully addressed anemia and hemolysis without an immediate increase in acute complications.

Frequently Asked Questions

How did Voxelotor in sickle cell disease affect hemoglobin levels in real-world settings?

According to the RETRO and PROSPECT registries, Voxelotor treatment led to a mean increase in hemoglobin levels ranging from 0.6 to 0.8 g/dL. These improvements were sustained over long-term follow-up periods of up to 54 months.

Did the registry studies show an increase in acute pain crises?

No, the registry analyses did not find evidence of an increased frequency of acute pain crises. In the PROSPECT registry, the annualized incidence rate of pain crises actually decreased from 4.78 pre-treatment to 3.15 post-treatment.

Why was the medication withdrawn from the market?

While registry data showed laboratory improvements, the drug was withdrawn globally in 2024 due to separate clinical trial data suggesting that the overall risks, including potential fatal events and vaso-occlusive crises in certain populations, outweighed the benefits.

Disclaimer: This content is for informational and educational purposes only. It does not constitute medical advice or a substitute for professional healthcare consultation. Refer to the latest local and national guidelines for clinical practice.

References

Andemariam B et al. Safety and effectiveness of voxelotor in individuals with sickle cell disease in the RETRO and PROSPECT US registries. Blood Adv. 2026 Feb 17. doi: undefined. PMID: 41701977.

Pfizer Inc. Pfizer Voluntarily Withdraws All Lots of Sickle Cell Disease Treatment OXBRYTA® (voxelotor) From Worldwide Markets. 2024 Sep 25.

Mahase E. Sickle cell drug is withdrawn over safety concerns just months after rollout. BMJ. 2024 Oct 1;387:q2147. doi: 10.1136/bmj.q2147.