The most appropriate maintenance therapy is infliximab. This patient's ulcerative colitis symptoms were refractory to mesalamine but have responded to prednisone, and he is doing well after the dose was tapered to 20 mg/d. Glucocorticoids are not effective for maintaining remission in ulcerative colitis. Therefore, in patients whose disease responds to glucocorticoids, the dose should be tapered while transitioning to a maintenance medication (azathioprine, 6-mercaptopurine, or an anti−tumor necrosis factor agent). Randomized controlled clinical trials have shown infliximab to be an effective maintenance therapy in patients such as this one.

Immunosuppression with azathioprine or 6-mercaptopurine is often used to maintain glucocorticoid-induced remission, but the data supporting this practice are scant. Moreover, this patient has a low thiopurine methyltransferase (TPMT) level, which indicates a high likelihood of severe bone marrow toxicity if exposed to azathioprine or 6-mercaptopurine. Azathioprine is converted in the body to 6-mercaptopurine, which is then either inactivated (by xanthine oxidase or TPMT) or activated to 6-thioguanine nucleotide. The level of TPMT should be checked before starting azathioprine or 6-mercaptopurine; 1 in 300 patients (0.3%) lack enzyme activity and are at high risk of toxicity. Azathioprine and 6-mercaptopurine should not be used in these patients.

Methotrexate may be used in the treatment of Crohn disease; however, there is no evidence for efficacy of methotrexate in ulcerative colitis.

Prednisone is not effective for maintenance of ulcerative colitis. In addition, long-term glucocorticoid use carries significant risk of side effects.