US drugmaker, Pfizer has announced the withdrawal of its sickle cell disease treatment, Oxbryta (voxelotor), from all markets where it had been approved. This move comes after concerns emerged about the drug’s safety, specifically an increased risk of serious complications and fatalities.
Pfizer acquired Oxbryta through its $5.4 billion purchase of Global Blood Therapeutics in 2022. The drug, designed to treat sickle cell disease, generated $328 million in revenue for Pfizer in 2023. However, based on recent clinical data, the company concluded that the risks of continuing treatment with Oxbryta outweighed its benefits. As a result, Pfizer is not only halting sales of the drug but also discontinuing all clinical studies and patient access programs related to it.
OXBRYTA, a once-daily oral treatment, was developed to enhance hemoglobin’s oxygen affinity, aiming to prevent the polymerization of sickle hemoglobin
Concerns Over Vaso-Occlusive Crisis and Fatal Events
The decision to pull Oxbryta follows concerns over an imbalance in the occurrence of vaso-occlusive crises—an extremely painful complication in sickle cell disease patients where blood flow is blocked, depriving tissues of oxygen and triggering inflammation. In addition to this complication, clinical trials revealed a disproportionate number of fatal events among those taking the drug. A study involving 236 patients showed eight deaths in the group treated with Oxbryta, compared to two deaths in the placebo group.
This revelation has prompted regulators worldwide to review the drug’s safety. The European Medicines Agency (EMA) scheduled an emergency meeting to discuss the risks, while the U.S. Food and Drug Administration (FDA) was also notified of the concerning findings.
Implications for Sickle Cell Treatment Options
Approved by the FDA in 2019 under its accelerated approval pathway, Oxbryta had offered new hope for sickle cell disease patients. It was also approved for use in Europe, the UK, and the UAE. The withdrawal of the drug leaves a gap in the treatment options available for patients.
Sickle cell disease is a hereditary disorder that affects the shape of red blood cells, causing them to become sickle-shaped, which can lead to severe health issues such as strokes, organ damage, and premature death. Traditional treatments for the condition include regular blood transfusions and the use of hydroxyurea to reduce the risk of blood vessel blockages. However, advancements in gene therapy have introduced new possibilities. In December 2023, the FDA approved two gene therapies as potential one-time treatments, developed by partnerships including Vertex and CRISPR Therapeutics, as well as Bluebird Bio.
