The most appropriate treatment is budesonide. Collagenous colitis, a form of microscopic colitis, is most often idiopathic, but in a small subset of patients it may be a side effect of medications. Drugs that have been highly associated with microscopic colitis include aspirin, acarbose, lansoprazole, NSAIDs, ranitidine, sertraline, and ticlopidine. Celiac disease is also associated with microscopic colitis. Treatment may be as simple as drug withdrawal or treatment of celiac disease. In mild persistent disease, antidiarrheal therapy such as loperamide or diphenoxylate can be used. In moderate disease, bismuth subsalicylate may be beneficial. This patient has collagenous colitis that has not responded to antidiarrheal therapy with diphenoxylate, loperamide, or bismuth subsalicylate. In patients with severe disease or in those that do not respond to antidiarrheal agents or bismuth, budesonide is the treatment of choice. It is highly effective (response rates of ≥80%). However, the risk of relapse is high once budesonide is stopped (70%-80%). Many patients require long-term maintenance therapy with low-dose budesonide or an immunomodulator such as azathioprine.

There is no evidence of benefit from antibiotics in collagenous colitis; therefore, ciprofloxacin is not appropriate for this patient.

In severe microscopic colitis, treatment with an anti–tumor necrosis factor agent such as infliximab may be effective. However, this expensive, potent immune-suppressing medication should be used only if budesonide is unsuccessful.

Open-label reports of mesalamine suggested a possible small benefit in microscopic colitis; however, a randomized trial showed no benefit compared with placebo.