Hazardous agent. Bone marrow suppression might occur (anemia, leukopenia, and thrombocytopenia). Use with caution in patients who have recently received other cytotoxic drugs or radiation therapy (possible additive myelosuppresive effects). Cutaneous vasculitic toxicities (vasculitic ulceration and gangrene) reported. Megaloblastic erythropoiesis might occur. Use with caution in renal impairment. When treated with hydroxyurea and antiretroviral agents (including didanosine) HIV-infected patients are at higher risk for potentially fatal pancreatitis, hepatotoxicity, hepatic failure, and severe peripheral neuropathy. Use of hydroxyurea in combination with antiretroviral agents not recommended. Possible self-limiting megaloblastic erythropoiesis. Hydroxyurea may delay plasma iron clearance and reduce rate of iron utilization by erythrocytes. Hydroxyurea-induced macrocytosis may mask incidental folic acid deficiency. Possible leukemia or secondary malignancies (e.g. sickle cell anemia, polycythemia vera). Skin cancer reported in patients receiving long-term therapy. May cause fetal harm. Highly toxic drug with low therapeutic index. Some geriatric patients may be more sensitive to the drug. Substantially eliminated by kidneys (increased risk of toxicity; use with caution).