Dapsone

Drug Interactions: Rifampin lowers dapsone levels 7 to 10-fold by accelerating plasma clearance; in leprosy this reduction has not required a change in dosage. Folic acid antagonists such as pyrimethamine may increase the likelihood of hematologic reactions. A modest interaction has been reported for patients receiving 100 mg dapsone daily in combination with trimethoprim 5 mg/kg q6h. On Day 7, the serum dapsone levels averaged 2.1 ± 1.0 μg/mL in comparison to 1.5 ± 0.5 μg/mL for dapsone alone. On Day 7, trimethoprim levels averaged 18.4 ± 5.2 μg/mL in comparison to 12.4 ± 4.5 μg/mL for patients not receiving dapsone.

Thus, there is a mutual interaction between dapsone and trimethoprim in which each raises the level of the other about 1.5 times. A crossover study 1 designed to assess the potential of a drug interaction between dapsone, 100 mg/day and trimethoprim, 200 mg every 12 hours, in eight asymptomatic HIV positive volunteers (average CD4 count 524 cells/mm 3 ) demonstrated that there was not a significant drug interaction between dapsone and trimethoprim.

However, an earlier report 2 also by Lee et al, in 78 HIV infected patients with acute Pneumocystis carinii pneumonia, receiving dapsone, 100 mg/day and higher trimethoprim dose, 20 mg/kg/day, demonstrated that the serum levels of dapsone were increased by 40% and trimethoprim levels were increased by 48% when the drugs were administered concurrently.

Pregnancy: Teratogenic Effects: Animal reproduction studies have not been conducted with dapsone. Extensive, but uncontrolled experience and two published surveys on the use of dapsone in pregnant women have not shown that dapsone increases the risk of fetal abnormalities if administered during all trimesters of pregnancy or can affect reproduction capacity. Because of the lack of animal studies or controlled human experience, dapsone should be given to a pregnant woman only if clearly needed. In general, for leprosy, USPHS at Carville recommends maintenance of dapsone. Dapsone has been important for the management of some pregnant D.H. patients.

Nursing Mothers: Dapsone is excreted in breast milk in substantial amounts. Hemolytic reactions can occur in neonates. See section on hemolysis. Because of the potential for tumorgenicity shown for dapsone in animal studies a decision should be made whether to discontinue nursing or discontinue the drug taking into account the importance of drug to the mother.