Hemolytic anemia (darkening of urine, marked fall in hemoglobin or erythrocyte count). Moderate-to-severe hemolytic reactions may occur in G6PD deficiency and personal or familial history of favism. Other hematologic effects (anemia, methemoglobinemia, and leukopenia) associated with primaquine use. Use with caution in known G6PD deficiency (use of aminoquinolines has been associated with hemolysis), and in NADH methemoglobin reductase deficiency (methemoglobinemia may occur).