Dapsone and leukemia

My dad is taking Dapsone only on weekends before Chemo., because he is allergic to sulfur drugs. As soon as he takes the medication, within one hour time he is weak, stomach pain, nausea, vomiting. The doctor cut the dosage down to two in the morning from four in the morning on Saturday and Sunday. He still is unable to take it without these symptoms. He has had Chronic Lymphocetic Leukemia for 8 years and has never had a problem like this. Has taken Chemo several times. This time he has started a new drug Fludabarine and now has hemolytic anemia or so they say. They told him that his ldh levels were normal during the whole ordeal so they are now confused. He had severe stomach pain. They gave him 4 units of blood and he seems to be doing well now. Do you think that Dapsone could be the cause of the Hemolytic anemia?