Optimizing thiopurine therapy in autoimmune hepatitis: A multicenter study on monitoring metabolite profiles and co-therapy with allopurinol
Jan Philipp Weltzsch, Claudius Bartel, Moritz Waldmann, Thomas Renné, Stephanie Schulze, Benedetta Terziroli Beretta‐Piccoli, Mária Papp, Ye Htun Oo, Vincenzo Ronca, Marcial Sebode, Ansgar W. Lohse, Christoph Schramm, Johannes Hartl
Abstract
BACKGROUND AND AIMS: In autoimmune hepatitis, achieving complete biochemical remission (CBR) with current weight-based thiopurine dosing is challenging. We investigated whether patients could be stratified regarding CBR according to a target range of thiopurine metabolites. Moreover, we explored the effects of azathioprine dosage increases and co-therapy of allopurinol with low-dose thiopurines on metabolite profiles and treatment response. APPROACH AND RESULTS: The relation between metabolites and treatment response was assessed in 337 individuals from 4 European centers. In a global, cross-sectional analysis, active metabolites 6-thioguanine nucleotides (6TGN) were similar in those with and without CBR. However, analyzing patients with sequential measurements over 4 years (N = 146) revealed higher average 6TGN levels in those with stable CBR (260 pmol/0.2 mL) compared to those failing to maintain CBR (181 pmol/0.2 mL; p = 0.0014) or never achieving CBR (153 pmol/0.2 mL; p < 0.0001), with an optimal 6TGN cutoff of ≥223 pmol/0.2 mL (sensitivity: 76% and specificity: 78%). Only 42% exhibited 6TGN ≥223 pmol/0.2 mL following weight-based dosing, as doses weakly correlated with 6TGN but with 6-methylmercaptopurine (6MMP), a metabolite associated with toxicity. Azathioprine dose increases led to preferential 6MMP formation (+127% vs. 6TGN +34%; p < 0.0001). Conversely, adding allopurinol to thiopurines in difficult-to-treat patients (N = 36) raised 6TGN (168→321 pmol/0.2 mL; p < 0.0001) and lowered 6MMP (2125→184 pmol/0.2 mL; p < 0.0001), resulting in improved transaminases in all patients and long-term CBR in 75%. CONCLUSIONS: Maintaining CBR in autoimmune hepatitis was associated with 6TGN ≥223 pmol/0.2 mL. For patients who fail to achieve CBR and therapeutic 6TGN levels despite thiopurine dose increase due to preferential 6MMP formation, comedication of allopurinol alongside low-dose thiopurines represents an efficient alternative.