Captopril is an investigational (experimental) drug that works by inhibiting the production of angiotensin II by blocking angiotensin converting enzyme. Reducing angiotensin II may reduce the bone marrow scar tissue in myelofibrosis. It is not approved by the Food and Drug Administration (FDA) for this indication. Participants in this study will be asked to have 2 bone marrow biopsies, a total of 3 blood samples, and fill out questionnaires asking about how you feel.
The purpose of this study is to evaluate the safety and tolerability of captopril and evaluate the effectiveness captopril as measured by changes in the grade of bone marrow scar tissue. The change in spleen size by ultrasound will also be measured.