Phase III studies have shown that patients with UC who received vedolizumab had a higher rate of clinical response, clinical remission and mucosal healing when compared to placebo3. Nevertheless, while clinical response rate was almost 50%, the rate of clinical remission at 6 weeks was only 16.9. In comparison, in the ACT trials almost 40% of patients achieved remission at week 84. The delayed onset of action of vedolizumab monotherapy in patients with UC may lead to a higher colectomy rate and limit the use of vedolizumab in patients with active disease who require rapid induction of remission. Corticosteroids are used as a bridging agent to rapidly induce remission. However, steroid refractory or dependent disease and steroid intolerance are common. Furthermore, steroids have devastating side effects.

Tacrolimus inhibits the complexion of calcineurin with its respective cytoplasmic receptors cyclophilin and FK-binding protein 12 (FKBP-12), both of which regulate a calmodulin dependent-phosphatase. Tacrolimus has been found to be efficacious in the treatment of patients with moderate to severe UC. Unfortunately, because of the safety profile with long term use, the drug is mostly used as an induction agent.

While switching to vedolizumab from another drug that has not been efficacious or has lost effectiveness (or starting vedolizumab as a first agent) can be beneficious in the long term, patients need an induction agent in order to achieve remission in a short period of time. Tacrolimus is a widely used drug to prevent implant rejection after a transplant. Randomized controlled trials have shown that is highly effective with good response rates even after 2 weeks of therapy. In order to avoid side effects, tacrolimus is usually used for a limited amount of time (12-14 weeks), which is sufficient time to induce remission of disease. Unfortunately, as other inflammatory bowel diseases, UC recurs and patients also require a maintenance therapy. While tacrolimus has been used with good results as a long term agent, the ideal scenario is to avoid its long term use as there is still a potential for side effects and a need for a very strict close monitoring. This is why a long term maintenance agent is needed to keep the patient in remission. Until recently, no ideal agent was available for this purpose, as while anti-tumor necrosis factor agents (infliximab and adalimumab) have been approved for ulcerative colitis, its combination with another agent that induces systemic immunosuppression (in this case, tacrolimus) could potentially increase the risk of infections and/or malignancies. Because vedolizumab is gut selective, does not affect the entire immune system and post-marketing studies have confirmed its safety profile. This makes it a perfect combination agent to tacrolimus, theoretically decreasing the potential side effect while increasing its efficacy.

The hypothesis is that the addition of tacrolimus as an induction agent to a standard regimen of vedolizumab increases the efficacy of the drug, decreasing the rate of need for colectomy and other complications while quickly improving the patients' quality of life without significantly increasing the risk of adverse events.