In a recent phase 3 trial, treatment of sickle cell disease with the drug voxelotor led to increased hemoglobin and decreased hemolysis markers. Results were published in the New England Journal of Medicine.

In this multicenter, double blind trial ( Identifier: NCT03036813), 274 patients with sickle cell disease were randomly assigned in a  1 to 1 to 1 ratio to receive a placebo or a daily dosage of either 900 mg or 1500 mg voxelotor, which helps to maintain hemoglobin in an oxygenated form and reduce sickling. The primary trial end point was the proportion of the intention-to-treat (ITT) population that achieved a greater than 1.0 g/dL rise in hemoglobin by week 24.

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Achieving the primary end point of hemoglobin response was significantly more common in patients receiving the 1500 mg dose of voxelotor compared with patients receiving placebo (51% [95% CI, 41%-61%] vs 7% [95% CI, 1%-12%]; P <.001). In patients receiving 900 mg voxelotor, 33% (95% CI, 23%-42%) met this end point.

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At week 24, the adjusted mean change in hemoglobin level was 1.1 g/dL (95% CI, 0.9-1.4) for patients in the ITT analysis receiving 1500 mg voxelotor (P <.001). The adjusted mean change was -0.1 g/dL (95% CI, -0.3 to 0.2) in patients receiving placebo and 0.6 g/dL (95% CI, 0.3-0.8) in patients receiving 900 mg voxelotor.

Voxelotor was associated in a dose-dependent manner with greater declines in the hemolytic markers of indirect bilirubin and reticulocyte percentage compared with placebo (P <.001 for both).

Most adverse events, including serious adverse events, did not vary greatly by group. Four fatalities occurred, 1 with each voxelotor dosage and 2 in the group receiving placebo; all fatalities were considered unrelated to the drug or placebo.

Voxelotor, particularly at the 1500 mg/d dosage, appeared effective at raising hemoglobin levels and inhibiting signs of hemolysis. “Voxelotor provided a significant, sustained increase in hemoglobin level and reduced the incidence of worsening anemia and hemolysis in patients with sickle cell disease,” the authors concluded.


  1. Vichinsky E, Hoppe CC, Ataga KI, et al. A phase 3 randomized trial of voxelotor in sickle cell disease [published online June 14, 2019]. N Engl J Med. doi:10.1056/NEJMoa1903212