How is dapsone used in the treatment of rheumatic diseases?
Dapsone is a sulfone. It is poorly water-soluble, poorly absorbed through the GI tract, and metabolized by the liver. It is used as an antimicrobial agent for leprosy treatment. However, it also has antiinflammatory effects and is particularly useful in dermatoses involving polymorphonuclear leukocytes. It is a free oxygen radical scavenger and impairs the myeloperoxidase system. In rheumatic diseases, it is particularly useful for skin vasculitis (leukocytoclastic, urticarial, or erythema elevatum diutinum, cutaneous polyarteritis nodosa), skin lesions of Behçet’s disease, SLE rashes (particularly bullous disease and panniculitis), relapsing polychondritis, and pyoderma gangrenosum. Doses range from 50 to 200 mg with an average of 100 mg/day. The major drug interaction is probenecid, which slows its renal excretion. Dapsone is also used as P. jiroveci prophylaxis in patients allergic to sulfa antibiotics.