A new clinical practice update recommends combination therapy with tumor necrosis factor (TNF) inhibitors and thiopurines, as opposed to either therapy alone, for the treatment of ulcerative colitis (UC) and Crohn’s disease (CD). The commentary was published in Gastroenterology.
Dr. Stephen B. Hanauer
Clinicians should also note that while several clinical trials use weight-based dosing to monitor clinical response following thiopurine therapy, 6-thioguanine levels have inevitably shown to better predict prognosis, wrote Stephen B. Hanauer, MD, AGAF, of Northwestern University in Chicago and his colleagues.
The thiopurine drug class is composed of many different agents, including thioguanine, azathioprine, and mercaptopurine. Methotrexate, a folate antagonist affecting thymidylate production, is commonly used alongside thiopurines as steroid-sparing agents for patients with UC and CD. Among these therapies, various different dosing strategies and routes of administration are used to manage active disease.
Initially, thiopurines were studied exclusively as monotherapy for the treatment of patients with steroid-intractable CD; however, results showed only marginal benefit when using these agents alone. As a result, combination trials were performed subsequently, and these revealed modest efficacy for use as maintenance therapies in both UC and CD. Further studies reported that methotrexate is beneficial only as a maintenance therapy for CD given that trial evidence confirmed treatment limitations in patients with UC.
“Thiopurines also have the potential to reduce postoperative recurrence of Crohn’s disease, in particular when administered with imidazole antibiotics,” the experts wrote. “There is currently no controlled data regarding the efficacy of methotrexate as maintenance therapy in ulcerative colitis,” they added.
Despite its limitations in UC, 25 mg of methotrexate administered intramuscularly once weekly in combination with oral steroids has shown benefits for inducing disease remission and limiting steroid use in the management of active CD. Comparatively, other trials have failed to show the same benefits with oral methotrexate. In addition, a number of clinical case series have reported benefit for use of methotrexate as a maintenance therapy for CD in patients who initially responded to methotrexate induction therapy.
Consequently, Dr. Hanauer and his colleagues recommended that methotrexate only be given in combination with biologics if being used for the treatment of UC.
“Thiopurines and methotrexate can be used in combination with anti-TNF biologics, in particular infliximab, to reduce immunogenicity and increase blood levels,” they stated.
One agent in particular, thioguanine, exhibits unique therapeutic efficacy in patients allergic to azathioprine or mercaptopurine. Despite this benefit, thioguanine use has been linked with an increased risk of developing hepatic nodular regenerative hyperplasia, as well as venoocclusive disease. Given these limitations, long-term use of thioguanine was not recommended by the authors.
With respect to safety, routine laboratory monitoring for both liver and hematologic adverse effects is recommended. In rare cases, patients may develop secondary lymphomas in response to thiopurine treatment. Moreover, regular follow-up is essential because of the higher prevalence of nonmelanoma skin cancers seen with thiopurines use.
“Patients using thiopurines for the treatment of IBD, particularly Caucasian patients, should avoid excessive sun exposure and use high-strength sun block,” the experts wrote. “Health care deliverers should ensure patients undergo appropriate dermatologic evaluations and investigate suspicious skin lesions in these patients,” they further reported.
Another important monitoring consideration is ongoing infection risk, in particular with opportunistic and viral pathogens. Because of the immunosuppressive effects of therapy, both methotrexate and thiopurine use are linked with a greater chance of developing these infections. Accordingly, Dr. Hanauer and his colleagues recommended that, before initiation of these therapies, applicable preventative measures should be taken, including administration of influenza, human papillomavirus, varicella zoster virus, pneumococcus, and hepatitis B vaccines.
“Live vaccines are contraindicated once therapy has begun; however, zoster vaccination can be given while patients are receiving azathioprine at less than 2 mg/kg,” they stated.
The experts went on to report that withdrawal of thiopurine agents, when used in combination therapy, has the potential to reduce therapeutic levels of infliximab and promote development of antidrug antibodies. However, the experts did not suggest a method to manage these complications. Further studies are needed to answer these and other remaining questions regarding thiopurine use in the setting of IBD.
SOURCE: Hanauer SB et al. Gastroenterology. 2018 Sep 6. doi: 10.1053/j.gastro.2018.08.043.
*This story was updated on January 4, 2019.