 1. Pharmacokinetics of 4-hydroxycyclophosphamide in Patients Receiving Cyclophosphamide for the SCOT trial Originally listed separately as DAIT SCSSc-01-01, NCT00848614. The purpose of this study is to determine the plasma concentration and exposure time required for cyclophosphamide to produce optimal immunosuppressive activity with minimal toxicity in participants with severe systemic sclerosis. 