Abstract
AMG 531 is a novel thrombopoeisis-stimulating peptibody that increases platelet production by targeting the thrombopoietin receptor. The trial described here is an ongoing, open-label, extension study of patients with immune thrombocytopenic purpura (ITP) assessing the safety and efficacy of long-term AMG 531 treatment of ITP, as well as patient-reported health-related quality of life (HRQOL). Eligible patients have completed a previous AMG 531 study in ITP. Patients previously treated with AMG 531 receive a starting dose that is the same as the final dose given in the previous study; placebo-treated patients begin the extension study with an AMG 531 dose of 1 μg/kg. The dose is skipped, decreased, maintained, or increased based on platelet count. Analysis was performed on the 36 patients (25 female, 11 male; 29 white, 6 Hispanic, 1 black) for whom complete data are currently available. The mean age is 50.0 ± 13.0 (SD) years. Most patients (83%) had a splenectomy prior to this study. HRQOL is being assessed with an ITP disease-specific measure, the ITP Patient Assessment Questionnaire (ITP-PAQ). This report describes the first use of the ITP-PAQ to measure treatment effect. The ITP-PAQ has 10 scales: 4 Physical Health (PH)—Symptoms, Fatigue, Bother, and Activity; 2 Emotional Health (EH)—Psychological and Fear; 3 Quality of Life (QOL)—Overall, Social, and Work; and 1 Women’s Reproductive Health (WRH). Each scale is scored 0 (worst)—100 (best). A planned interim analysis was conducted to evaluate changes in HRQOL from week 1 (pretreatment) to week 24. Results indicated improvement in the areas of PH-Symptoms, with a 7.9-unit increase (p=0.007), PH-Fatigue, with a 7.8-unit increase (p=0.006), PH-Bother, with a 9.4-unit increase (p=0.025), PH-Activity, with a 7.4-unit increase (p=0.032), and QOL-Work, with a 7.9-unit increase (p=0.014). An analysis of minimal clinically important difference will be conducted when the sample size is large enough to determine if statistically significant values are clinically meaningful. A comparison of HRQOL in patients with a durable platelet response (doubling of the baseline count and ≥50×109/L at 6 or more weeks during weeks 17–24 in the absence of rescue medication) versus those without a durable response showed a trend for greater improvement among the responders in all 10 scales, with significant differences for PH-Symptoms (p=0.02), PH-Bother (p=0.02), PH-Activity (p=0.01), EH-Psychological (p=0.01), and QOL-Overall (p=0.03). Individualized dosing of AMG 531 provides a unique therapeutic option for managing platelet count in ITP while improving HRQOL.
A disease-specific measure of health-related quality of life for use in adults with immune thrombocytopenic purpura: Its development and validation
