Dapsone is an approved oral antibiotic drug. It can be used in combination with trimethoprim for treating Pneumocystis pneumonia (PCP), and may be used as PCP prophylaxis for people who cannot tolerate co-trimoxazole (Septrin)^[1]. It is often used in combination with pyrimethamine (Daraprim) to prevent of toxoplasmosis and PCP, since these two drugs enhance each other’s activity^[2]. GlaxoSmithKline manufactures a combination of these two drugs in one tablet under the trade name Maloprim.

Dapsone with pyrimethamine also reduces the incidence of Mycobacterium avium intracellulare and tuberculosis^[3].

Dapsone remains at a high level in the body for a long time after each dose is taken, so weekly or twice weekly dosing may thus be justified, although this dosing is controversial^[4]. It is best taken with food to avoid nausea. Once-weekly dosing produces adequate drug levels in HIV-positive children, although daily dosing may be more effective in preventing PCP^[5][6].

Dapsone causes a relatively high rate of allergic skin rashes^[7]. Other side-effects include nausea and blood disorders. A comparative study of dapsone and atovaquone (Wellvone) for the prevention of PCP found that among people who were not previously on dapsone, atovaquone caused fewer side-effects^[8].

The absorption of dapsone may be reduced if the level of acid in the stomach is below normal. This may happen in people who have low levels of acid in the stomach or if it is taken at the same time as the anti-HIV drug ddI (didanosine, Videx / VidexEC), which includes an antacid in its formulation. People taking both dapsone and ddI should take the dapsone at least two hours before or after the ddI.