Children and teens on chemotherapy take antibiotics 2 to 3 days each week to prevent pneumocystis pneumonia (PCP). They usually continue taking the antibiotics for a few months to a year after treatment ends. The antibiotic of choice for PCP prevention is a combination drug containing sulfamethoxazole and trimethoprim; it is sold under the brand names Bactrim® and Septra®. This antibiotic can cause gastrointestinal upset, skin rashes, sun sensitivity, and low blood counts. If a substitute is needed, one of the following is used:

• Pentamidine, administered as an aerosol or through a nebulizer (can be difficult for children because it takes 20 minutes to administer and it smells and tastes bad), or by IV once a month.
• Dapsone®, pills given orally every day.