Antibiotics generally considered for antibacterial prophylaxis for immunosuppressed patients are trimethoprim-sulfamethoxazole and the quinolones. Trimethoprim-sulfamethoxazole can significantly reduce infections and is highly effective in preventing pneumonia due to Pneumocystis carinii. However, it can cause sulfonamide-related reactions, myelosuppression, oral candidiasis, and development of bacterial resistance, and it lacks activity against Pseudomonas aeruginosa. Quinolones can reduce the occurrence of fever and infections in patients with neutropenia but do not provide adequate coverage against gram-positive bacteria, and inappropriate use can induce resistance among gram-negative organisms. Routine antibacterial prophylaxis is not recommended for patients likely to develop neutropenia. Antifungal prophylaxis is appropriate in settings in which fungal infections are frequent. Fluconazole is recommended for patients who are to undergo hematopoietic stem cell transplantation; it can be considered for elderly patients with acute leukemia who are to receive intensive chemotherapy. Itraconazole can also be used. Prophylaxis with antiviral agents is generally not indicated; however, it should be given to hematopoietic stem cell transplant recipients.