A 50-year-old male presents with 1 day of diarrhea (3-4 watery stools) after self-administering 6 tablets of furazolidone. The next day, he developed chills, fever, dizziness, and passed tea-colored urine once. Physical exam: severe anemic appearance, icteric sclera, no hepatosplenomegaly. Laboratory tests: Hb 60g/L, reticulocytes 20.1%, positive urine occult blood, positive methemoglobin reduction test. Similar episode occurred 20 years ago after taking sulfonamides for fever, resolved spontaneously in 1 week without treatment. The most likely diagnosis is: