Pfizer’s Withdrawal of SCD Drug Raises Questions

The global withdrawal of voxelotor (Oxbryta, Pfizer) has left clinicians who treat sickle cell disease (SCD) with the urgent task of reaching patients taking the medicine, while trying to understand why it was taken off the market.

The National Alliance of Sickle Cell Centers issued a statement urging patients not to stop voxelotor abruptly. Instead, they should work out plans with their physicians and medical teams for weaning plans.

“Don’t lose faith. This a step backward, but we will stay on the path to better outcomes for everyone,” said the alliance in a statement to patients and clinicians.

On September 25, Pfizer said it would withdraw all lots of voxelotor in all markets where it is approved. The New York–based drugmaker also said it was discontinuing all active voxelotor clinical trials and expanded access programs worldwide. The cause was data that suggested “an imbalance in vaso-occlusive crises and fatal events which require further assessment.”

Pfizer told Medscape Medical News in an email exchange that it is focused on analyzing the data and will share updates in the future about presenting or publishing on this issue.

The withdrawal came amid increased scrutiny of the drug by the European Medicines Agency (EMA). The EMA in July began a review of voxelotor after data from a clinical trial showed that a higher number of deaths occurred with the drug than with placebo and another trial showed the total number of deaths was higher than anticipated.

On September 26, the EMA’s human medicines committee recommended suspending the marketing authorization of voxelotor, citing new safety data that emerged during the review. The drug had received marketing authorization for the European Union in 2022, the agency said.

The US Food and Drug Administration (FDA), which first cleared voxelotor for sale in 2019, also said it has been conducting a safety review of the drug. The agency continues to examine post-marketing clinical trial data for voxelotor, the real-world registry studies, and data from the FDA Adverse Event Reporting System. At the conclusion of this review, the FDA will communicate any additional findings, if necessary, the agency said.

The FDA said it appeared that more deaths and a higher rate of vaso-occlusive crisis occurred in patients taking voxelotor vs placebo in post-marketing clinical trials.

“Pfizer also observed a higher rate of vaso-occlusive crisis in patients with sickle cell disease receiving Oxbryta in two real-world registry studies,” the FDA said. “Based on the totality of clinical data, Pfizer has determined the benefit of Oxbryta does not outweigh the risk.”

Gene Therapy, Tried-and-True Hydroxyurea (HU)

As a field, SCD has drawn more interest in recent years, with significant gains made lately in cutting-edge projects.

The FDA in December approved two gene-editing treatments for patients aged 12 years or older. These are considered “milestone treatments” for a debilitating and potentially life-threatening blood disorder that affects about 100,000 people in the United States. Exagamglogene autotemcel (Casgevy, Vertex Pharmaceuticals and CRISPR Therapeutics) is the first to use the gene-editing tool CRISPR. And lovotibeglogene autotemcel (Lyfgenia, bluebird bio) uses a different gene-editing tool called a lentiviral vector.

These advances have been covered widely by the news media but are not expected to be widely available, with the cost of these extensive treatments estimated around $2-$3 million per patient.

“Gene therapy is amazing in that it can offer a cure, but it’s very expensive and not all patients are suitable for it. Some have so much existing organ damage that it’s not an option for them,” said John Wood, MD, PhD, director of cardiovascular MRI at Children’s Hospital Los Angeles, Los Angeles, who does research on SCD.

“So it really is a great treatment for a very few people,” he said in an interview.

The mainstay of treatment for SCD remains a drug that Lydia Pecker, MD, a pediatric hematologist at Johns Hopkins University in Baltimore, describes as the “first, oldest, and best”: HU.

The FDA approved this in 1998 for use in SCD. It reduces the frequency of painful crises and acute chest syndrome and other complications of SCD that otherwise could be serious or even lethal, Pecker said.

“Older doctors can tell you that what they experienced with sickle cell disease in the hospitals has been completely transformed because of the high uptake of the drug,” she said, adding that it made a “profound” change. “We just don’t have data for any other agent that’s quite like that.”

Voxelotor had been a good second drug to add for some patients, in addition to HU and blood transfusions, Pecker noted. It was a first-line drug for those for whom transfusion and HU were not options, which constitutes a relatively small number of patients, she said.

“So we have, in the last 5 years, felt more hopeful because we had something else to offer,” she said.

Alexis A. Thompson, MD, MPH, chief of the Division of Hematology at Children’s Hospital of Philadelphia, Philadelphia, told Medscape Medical News that her organization also had patients who appeared to benefit from voxelotor, some of whom had been participants in clinicals trials.

Thompson, who has been a top researcher involved in the study of gene therapy, urged the need for companies to keep seeking to expand the options for people with SCD, even after the setback with voxelotor.

“I hope that there’s an appreciation for the need for continued investment in this very serious condition, for which there are insufficient options for treatments,” Thompon said. “So ongoing investment is really needed if we expect to make progress.”

Pecker disclosed ties with Novartis, Afimmune, the American Society of Hematology, and the National Institutes of Health. Thompson reported relationships with bluebird bio, Beam, Editas, Novartis, and Novo Nordisk.

Kerry Dooley Young is a freelance journalist based in Washington, DC. You can follow her on LinkedIn.