Corticosteroids and azathioprine provide complete response with good tolerance in most patients for the treatment of autoimmune hepatitis (AIH).1European Association for the Study of the Liver EASL Clinical Practice Guidelines: autoimmune hepatitis.J Hepatol. 2015; 63: 971-1004Google Scholar, 2Manns M.P. Czaja A.J. Gorham J.D. et al.Diagnosis and management of autoimmune hepatitis.Hepatology. 2010; 51: 2193-2213Google Scholar Although some patients require second-line treatments, scarce data and side effects hamper consensus on which treatment to use as second-line treatment. Studies in inflammatory bowel disease are increasingly considering the use of 6-mercaptopurine (6-MP) or 6-thioguanine (6-TG), which both exhibit a more direct metabolism to the active metabolite of azathioprine: 6-TG nucleotides.3Karran P. Attard N. Thiopurines in current medical practice: molecular mechanisms and contributions to therapy-related cancer.Nat Rev Cancer. 2008; 8: 24-36Google Scholar Data regarding thiopurines substitution as a second-line therapy for AIH are limited and even more so regarding 6-TG. We herein report our experience with 6-TG after azathioprine failure or intolerance. Hospital database was searched for adult patients treated with 6-TG for AIH (according to International Autoimmune Hepatitis Group simplified score ≥6). Files were reviewed to collect clinical and biologic data. 6-TG (20 mg/day) was introduced as second- or third-line therapy because of failure or intolerance to azathioprine. Because of missing data on IgG during follow-up, efficacy was evaluated as maintained biologic response defined by normal serum transaminases after corticosteroid withdrawal. Relapse was defined by an increase of serum transaminases higher than 1.2 times the upper normal range, and/or reintroduction of corticosteroids. To assess nodular regenerative hyperplasia (NRH) the initial and follow-up liver biopsies (LB) were reticulin stained and reviewed by 2 pathologists blinded to the patient’s data. Seventeen patients were treated with 6-TG; their baseline characteristics are described in Table 1. Discontinuation of azathioprine occurred after 2 (1.3–4.2) months because of intolerance (digestive, 11 patients; cutaneous, 3 patients; hematologic, 2 patients), or nonresponse (1 patient). Eleven patients received 6-TG as second-line therapy. For 6 patients second-line therapy was mycophenolate mofetil (MMF), but was afterward switched to 6-TG because of incomplete response (5 patients) or intolerance (1 patient).Table 1Population CharacteristicsAge, y54 [46–68]Sex (F/M)11 (64.7)/6(35.3)Follow-up time, mo20.5 [10–51]Median AIH score6 [6–7]Histologic fibrosisF0: 0 (0)F1: 6 (35)F2: 3 (18)F3: 4 (23.5)F4: 4 (23.5)Overlap syndrome2 (12)AST, UI/L538 [52–909]ALT, UI/L609 [285–1564]γ-GT, g/L313 [180–528]ALP, UI/L162 [128–432]Total bilirubin, μmol/L41 [21.7–111]Prothrombin time, %90 [86–98]IgG, g/L15.3 [13–21.7]γ-Globulins, g/L15.2 [13.2–17]Antinuclear antibody >1/8011 (64.7)Anti–smooth muscle antibody >1/808 (47)NOTE. Results are expressed as median [25th–75th percentile] or n (%).ALP, alkaline phosphatase; ALT, alanin aminotransferase; AST, aspartate aminotransferases; γ-GT, γ-glutamyltransferase. Open table in a new tab NOTE. Results are expressed as median [25th–75th percentile] or n (%). ALP, alkaline phosphatase; ALT, alanin aminotransferase; AST, aspartate aminotransferases; γ-GT, γ-glutamyltransferase. The side effects for which azathioprine was discontinued regressed in all patients after initiation of 6-TG. Sixteen patients had normalization of transaminases within 3 months, whereas 1 patient had to disrupt 6-TG after 1 month because of dry-eye syndrome. Maintained biologic response occurred in 11 (64%) patients. One patient was lost to follow-up during corticosteroids tapering, and 1 although a responder had anemia prompting cessation of 6-TG after 13 months. Four patients relapsed, including the patient with previous azathioprine failure. Corticosteroids were reintroduced, with normalization of transaminases and successful tapering for 1 patient, whereas the 3 others did not responded leading to 6-TG cessation and switch for tacrolimus or MMF. Besides the 2 (11%) patients with dry-eye syndrome and anemia, no clinical side effects were observed. One patient with cirrhosis had cytopenia that regressed after decreasing 6-TG to 10 mg/day. Eight patients had LB after a median 6-TG treatment time of 35 (20–52) months. One patient whose LB before 6-TG treatment showed sinusoidal fibrosis and thickening of the hepatic vein wall showed signs of NRH after 10 months of 6-TG, without clinical portal hypertension. Two patients had worsening fibrosis; 1 had stopped 6-TG after 1 month, and 1 had relapsed. Azathioprine is the treatment for which long-term data are the most available,1European Association for the Study of the Liver EASL Clinical Practice Guidelines: autoimmune hepatitis.J Hepatol. 2015; 63: 971-1004Google Scholar, 2Manns M.P. Czaja A.J. Gorham J.D. et al.Diagnosis and management of autoimmune hepatitis.Hepatology. 2010; 51: 2193-2213Google Scholar therefore treatments based on the same metabolic pathway have a logical relevance. Furthermore, the direct metabolism of 6-TG to 6-TG nucleotides avoids enzymatic variability because of genetic polymorphism, and avoids some metabolites inducing azathioprine intolerance. Moreover, similarly to azathioprine, monitoring of 6-TG nucleotides may allow treatment optimization. MMF is a well described second-line therapy in AIH, with efficacy ranging from 39%–71% in azathioprine-intolerant patients.4Hennes E.M. Oo Y.H. Schramm C. et al.Mycophenolate mofetil as second line therapy in autoimmune hepatitis?.Am J Gastroenterol. 2008; 103: 3063-3070Google Scholar, 5Richardson P.D. James P.D. Ryder S.D. Mycophenolate mofetil for maintenance of remission in autoimmune hepatitis in patients resistant to or intolerant of azathioprine.J Hepatol. 2000; 33: 371-375Google Scholar Our results with 6-TG show similar success rate (64%) with favorable tolerance compared with MMF, which induces gastrointestinal side effects in 12%–50% or leukopenia in 7% of patients.4Hennes E.M. Oo Y.H. Schramm C. et al.Mycophenolate mofetil as second line therapy in autoimmune hepatitis?.Am J Gastroenterol. 2008; 103: 3063-3070Google Scholar, 5Richardson P.D. James P.D. Ryder S.D. Mycophenolate mofetil for maintenance of remission in autoimmune hepatitis in patients resistant to or intolerant of azathioprine.J Hepatol. 2000; 33: 371-375Google Scholar Safety of 6-TG is debated because of NRH. However, results are discrepant and NRH has been reported without azathioprine treatment.6van Asseldonk D.P. Jharap B. Verheij J. et al.The prevalence of nodular regenerative hyperplasia in inflammatory bowel disease patients treated with thioguanine is not associated with clinically significant liver disease.Inflamm Bowel Dis. 2016; 22: 2112-2120Google Scholar, 7De Boer N.K.H. Tuynman H. Bloemena E. et al.Histopathology of liver biopsies from a thiopurine-naïve inflammatory bowel disease cohort: prevalence of nodular regenerative hyperplasia.Scand J Gastroenterol. 2008; 43: 604-608Google Scholar In our study, 1 of 8 patients with LB exhibited NRH. Interestingly, some vascular changes existed before 6-TG treatment, which taking into account the short course of treatment received might suggest resulting in NRH associated factors resulting in NRH. Longer follow-up and larger cohort are required to assess this issue. Hübener et al8Hübener S. Oo Y.H. Than N.N. et al.Efficacy of 6-mercaptopurine as second-line treatment for patients with autoimmune hepatitis and azathioprine intolerance.Clin Gastroenterol Hepatol Off Clin Pract J Am Gastroenterol Assoc. 2016; 14: 445-453Abstract Full Text Full Text PDF Scopus (66) Google Scholar recently showed the relevance of 6-MP as a second-line treatment in AIH. Although response rate was similar to our results, the initial side effects recurred in 25% of patients, whereas in our study they were rare (11%) and differed from those experienced with azathioprine. This may be because contrary to 6-TG, 6-MP still shares metabolites with azathioprine. Similarly to our study, nonresponders to azathioprine did not respond to 6-MP. In conclusion, our results show that 6-TG could be considered as a relevant option for second-line therapy for AIH in azathioprine-intolerant patients.