Methemoglobinemia
Cases of methemoglobinemia, with resultant hospitalization, have been reported postmarketing in association with twice daily dapsone gel, 5% treatment. Patients with glucose-6-phosphate dehydrogenase deficiency or congenital or idiopathic methemoglobinemia are more susceptible to drug-induced methemoglobinemia. Avoid use of dapsone gel, 7.5% in those patients with congenital or idiopathic methemoglobinemia.
Signs and symptoms of methemoglobinemia may be delayed some hours after exposure. Initial signs and symptoms of methemoglobinemia are characterized by a slate grey cyanosis seen in e.g., buccal mucous membranes, lips, and nail beds. Advise patients to discontinue dapsone gel, 7.5% and seek immediate medical attention in the event of cyanosis.
Dapsone can cause elevated methemoglobin levels particularly in conjunction with methemoglobin-inducing agents
[see Drug Interactions (7.4)].
Hemolysis
Oral dapsone treatment has produced dose-related hemolysis and hemolytic anemia. Individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency are more prone to hemolysis with the use of certain drugs. G6PD deficiency is most prevalent in populations of African, South Asian, Middle Eastern, and Mediterranean ancestry.
In clinical trials, there was no evidence of clinically relevant hemolysis or hemolytic anemia in subjects treated with topical dapsone. Some subjects with G6PD deficiency using dapsone gel, 5% twice daily developed laboratory changes suggestive of hemolysis
[see Use in Specific Populations (8.6)].
Discontinue dapsone gel, 7.5%, if signs and symptoms suggestive of hemolytic anemia occur. Avoid use of dapsone gel, 7.5% in patients who are taking oral dapsone or antimalarial medications because of the potential for hemolytic reactions. Combination of dapsone gel, 7.5%, with trimethoprim/sulfamethoxazole (TMP/SMX) may increase the likelihood of hemolysis in patients with G6PD deficiency
[see Drug Interactions (7.1)].