Real World Evidence of Prescription Patterns and Effect of Oxbryta (voxelotor) for Patients with Sickle Cell Disease

Background: Sickle cell disease (SCD) is a chronic illness characterized by anemia, recurrent severe pain and recurrent organ damage, affecting approximately 100,000 persons in the United States. Prior to November 2019, FDA approved SCD disease-modifying treatments included only hydroxyurea (HU) and L-glutamine. However, voxelotor (Oxbryta®) was recently approved under an accelerated approval based on the HOPE study for the treatment of adult and pediatric patients with SCD 12 years of age and older. We aimed to provide real world evidence of the types of patients prescribed voxelotor and preliminary evidence of potential treatment effects.

Methods: Patient records were reviewed from five medical centers with comprehensive sickle cell care. All patients prescribed voxelotor from Nov 25, 2019 to July 31, 2020 were included in our analysis. Data reviewed included: patient demographics, hydroxyurea use, as well as pre- and post- voxelotor changes on red cell transfusion number, vaso-occlusive crisis (VOC) and hemoglobin (Hb) values. In addition, voxelotor dosage changes, side effects, and patients perception on impact on their health were recorded. Descriptive and summary statistics were used to provide results.

Results: We reviewed data from 60 patients (18 pediatric and 42 adult), across the five centers, who were prescribed voxelotor. Mean age was 33 (SD 13.8) years old with 63% female patients. All patients were African-American/Black and 96% were HbSS (2% Hb SC and 2% HbSOArab). Eighty (80)% were on hydroxyurea, 20% were on chronic transfusions, and 10% were on erythropoietin stimulating agents when prescribed voxelotor. Mean baseline hemoglobin during the 3 months prior to initiation was 7.38 g/dL (SD 1.46) with all patients started at the recommended dose of 1500mg. Annualized VOC events for the year prior to starting voxelotor was 0.62 (SD) or 7.44 VOCs per year.

Across all sites, 31 patients were prescribed voxelotor but had either not initiated drug, not returned for follow up labs at time of analysis, or refused to take drug once approved (n=1). Nine patients had only 1 month of follow labs to review and an additional 18 patients with 3 months of follow up labs. These 27 patients were followed for an average of 6.0 months (SD 7.7) on treatment with 4 patients (15%) requiring dose adjustment to 1000mg. Dose adjustments were for side effects including abdominal pain, diarrhea, loose stools and nausea/vomiting. One patient had dosing changed from daily to three times a day. Average hemoglobin during steady state after 1 and 3 months of treatment were 8.6 g/dL (SD 1.8) and 8.0 g/dL (SD 1.8), respectively. In addition, 52% increased by 1g/dL at 1 month (n=21) and 44% increased by 1g/dL at 3 months (n=18). The mean maximum hemoglobin obtained during the 3-month period following initiation of voxelotor was 8.9 (SD 2.1) g/dL. During follow up visits, several patients reported 'more energy' and improvement in 'morning achiness' and 'quality of life', while a few patients noted no change in stamina or well-being. Three patients (5%) had drug discontinued due to becoming pregnant, unexplained elevation of liver enzymes, and due to excessive abdominal pain and nausea. Annualized VOC rates after voxelotor initiation were numerically decreased, although limited by short follow up.

Conclusion: We present real world evidence of prescribing patterns and initial outcomes from the use of newly approved voxelotor. We found the majority of patients prescribed voxelotor were the HbSS genotype, on hydroxyurea, and with a mean baseline Hb <7.5 g/dL, indicating an initial focus on more anemic patients. Interestingly, one-fifth of the prescribed patients where on chronic transfusions. Consistent with the HOPE trial, the average Hb levels was found to have increased at 1 month and 3-month follow up. Our preliminary results support an overall increase in hemoglobin in patients treated with voxelotor and we aim to continue following patients over a longer follow up period. This provides important real-world evidence for this newly approved disease-modifying therapy for SCD.