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Pfizer is pulling its sickle cell disease (SCD) treatment voxelotor (Oxbryta) from global markets after data review showed an imbalance in deaths among patients taking the drug.

"The overall benefit of the drug no longer outweighs the risk in the approved sickle cell patient population," the on Wednesday, adding that the imbalance in fatal events and severe pain complications common to the inherited blood disorder will require further assessment.

“Healthcare professionals should stop prescribing Oxbryta,” the FDA said in a on Thursday, adding that patients and caregivers should contact their providers about switching treatments.

In July, the launched a review of voxelotor after data from clinical trials showed more fatalities than would be expected among patients taking the drug.

In one trial involving 236 patients with SCD and an increased risk for stroke, there were eight deaths in the group assigned to voxelotor versus two among placebo recipients. And in an 88-patient trial evaluating the effect of the medicine on leg ulcers, a complication of SCD, eight deaths were reported during the open-label portion of the study -- a figure higher than anticipated.

FDA also reported that Pfizer observed a higher rate of vaso-occlusive crisis in SCD patients receiving voxelotor in two real-world registry studies.

In the U.S., the hemoglobin S (HbS) polymerization inhibitor was granted accelerated approval for SCD in 2019 based on data from the phase III HOPE trial, which showed a better hemoglobin response with voxelotor versus placebo. As deoxygenated HbS polymerization drives SCD pathophysiology, the thinking was that inhibition would translate to clinical benefit.

But the trial only showed a non-significant trend in the key secondary endpoint of vaso-occlusive crises, the severe and common pain complications of SCD. As part of the accelerated approval pathway, companies are typically required to verify a drug's clinical benefit for continued approval.

In addition to removing all lots of voxelotor from worldwide markets, Pfizer said that clinical trials and expanded access programs will be discontinued globally as well.

"We believe this action is in the best interest of patients," Aida Habtezion, MD, the company's chief medical officer and head of global safety, said in a release. "Our primary concern is for patients who suffer from SCD, which remains a very serious and difficult-to-treat disease with limited treatment options. We advise patients to contact their physicians to discuss alternative treatment while we continue to investigate the findings from our review of the data."

Voxelotor received FDA approval for adults and children ages 4 years and up. In its release, FDA noted that there are other approved medications available for SCD.

Recent approvals include crizanlizumab (Adakveo) for adults and pediatric patients ages 16 years and older, as well as two gene therapies — exagamglogene autotemcel (Casgevy) and lovotibeglogene autotemcel (Lyfgenia) — for adults and children ages 12 years and older.

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