SYLVANT, with the generic name siltuximab, is a prescription medication used in the treatment of a rare disease known as multicentric Castleman's disease (MCD) in patients who do not have HIV or human herpesvirus 8 (HHV-8). It is classified as a monoclonal antibody, specifically targeting and neutralizing interleukin-6 (IL-6), a cytokine involved in the abnormal immune response associated with MCD. By inhibiting the action of IL-6, SYLVANT helps to reduce the excessive proliferation of lymphocytes and the systemic symptoms associated with MCD, such as fever, night sweats, weight loss, and lymphadenopathy. Administered through intravenous infusion, SYLVANT offers a targeted approach to managing this complex condition, providing an essential treatment option for patients affected by MCD.