Positive Results from Part A of a Phase 3 Trial for Sickle Cell Disease

Sickle cell disease (SCD) is a blood disorder. SCD patients have abnormal hemoglobin, or sickle hemoglobin, caused by a genetic mutation in the beta-chain. It results in deformed and inflexible blood cells, the blocking of capillaries, and the blocking of blood vessels, wreaking havoc on the body. Patients undergo episodes of severe pain as a result of the blocked blood flow to major organs. This means patients can experience psychosocial and physical disabilities. Ultimately, SCD causes organ damage and often leads to early death.

Researchers have been hard at work to find an effective treatment for SCD, and recent results from part of a Phase 3 trial have brought renewed hope to this community. The treatment is called Voxelotor.


Voxelotor works to block polymerization of blood cells by increasing the blood’s affinity for oxygen. Oxygenated blood cells don’t polymerize, meaning that Voxelotor could stop polymerization and the resulting sickling of hemoglobin. It’s being investigated as a once-daily therapy, taken orally. Voxelotor has already received Orphan Drug and Rare Pediatric Disease designation, Breakthrough Therapy designation, and Fast Track designation by the FDA.

Part A of The Trial 

Global Blood Therapeutics, Inc. (GBT) has been working on a study of 154 children and adults with SCD to test the efficacy of Voxelotor. In Part A of the Phase 3 trial, Voxelotor was administered for 24 weeks in participants 12 years and older. Preliminary results showed drastic improvements in hemoglobin levels. 65% of patients who were given 1500mg of Voxelotor had more than a 1 g/dL increase in hemoglobin by the end of the trial. Additionally, 33% who were given just 900mg of the drug achieved the same results. For those patients given placebo, only 10% showed this improvement. The increases in hemoglobin for patients taking Voxelotor were rapid and sustained.

The study also showed improvements in hemolysis and anemia, meaning Voxelotor has the potential to prevent organ damage in patients. Currently for SCD patients, that is the leading cause of death. Additionally, the safety profile of the drug was found to be favorable in this study. No evidence was found showing impairment of tissue oxygenation while using the drug.

The Rest of the Trial

Part B of this trial will examine the effect of Voxelotor over 24 weeks at the same doses as Part A, but in 36 patients 12-17 years old. Part C will evaluate just the 1500mg dose for patients 4-17 years of age for 48 weeks. This last segment of the trial is still enrolling patients. They expect to enroll up to 50 participants.

You can read more about GBT’s Phase 3 trial of Voxelotor here and stay tuned for updates on Part B and C!

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