Tag Archives: 6-thioguanine level

Adjustment of azathioprine dose in NUDT15 intermediate metabolizers, COVID-19 in Georgia & COVID-19 Phase 1 Vaccine Study

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LA Jackson et al. NEJM 2020; DOI: 10.1056/NEJMoa2022483. Link:  An mRNA Vaccine against SARS-CoV-2 — Preliminary Report  The mRNA-1273 vaccine induced anti–SARS-CoV-2 immune responses in all participants (n=45), and no trial-limiting safety concerns were identified.

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COVID-19 in Georgia (Data from 7/13/20):

B Kang et al. AP&T 2020; https://doi.org/10.1111/apt.15810. Thanks to Ben Gold for this reference. Full text: Adjustment of azathioprine dose should be based on a lower 6‐TGN target level to avoid leucopenia in NUDT15 intermediate metabolizers

Background: “In addition to TPMT polymorphisms, a recent genome‐wide association study reported that a missense variant of nudix hydrolase 15 (NUDT15 ), which encodes a novel thiopurine‐metabolizing enzyme, was strongly associated with thiopurine‐induced leucopenia especially in Asians”

Key findings:

  • Among the 167 pediatric patients included, leucopenia was observed in 16% (19/119), 44% (20/45) and 100% (3/3) of the NUDT15 normal, intermediate and poor metabolizers respectively (P  < 0.001)
  • There was a positive association between 6‐TGN levels and leucopenia among the NUDT15 intermediate/TPMT normal metabolizers
  • In order to reduce the development of thiopurine‐induced leucopenia (<15%) in NUDT15 intermediate metabolizers, adjustment of azathioprine doses should be based on a lower 6‐TGN target level (<167.1 pmol/8 × 108 RBC)

Limitations: single-center, retrospective study and possible selection bias

My take: While 6-TGN levels between 235-400 are typically considered therapeutic, individuals with intermediate metabolism are at increased risk for leukopenia and may respond at lower levels.  This study indicates that careful dosing and close monitoring is needed for NUDT15 intermediate metabolizers

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Disclaimer: This blog, gutsandgrowth, assumes no responsibility for any use or operation of any method, product, instruction, concept or idea contained in the material herein or for any injury or damage to persons or property (whether products liability, negligence or otherwise) resulting from such use or operation. These blog posts are for educational purposes only. Specific dosing of medications (along with potential adverse effects) should be confirmed by prescribing physician.  Because of rapid advances in the medical sciences, the gutsandgrowth blog cautions that independent verification should be made of diagnosis and drug dosages. The reader is solely responsible for the conduct of any suggested test or procedure.  This content is not a substitute for medical advice, diagnosis or treatment provided by a qualified healthcare provider. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a condition

6-Thioguanine Levels in Autoimmune Hepatitis

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A recent retrospective study (MA Sheiko et al JPGN 2017; 65: 80-5) examines the issue of azathioprine (AZA) metabolites and outcomes in pediatric autoimmune hepatitis (AIH).

Study characteristics:

  • 66 children
  • Mean age of diagnosis 9.6 years
  • Mean follow-up 2.9 years
  • Study period 2002-2013

Key findings:

  • 79% achieved biochemical remission (defined as ALT ≤50 U/L); mean time was 6.2 months
  • 6% required liver transplantation
  • 18% were weaned off immunosuppression and remained in remission
  • 6-thioguanine (6-TGN) levels ranging from 50 to 250 (pmol/8 x 10 to 8th red blood cell count) were associated with biochemical remission

“Our study suggests that AZA dosing of approximately 1.2 to 1.6 mg/kg/day will achieve 6-TGN levels of 50 to 250 pmol, which is sufficient to maintain biochemical remission in the majority of patients.“

This is significantly lower than dosing recommended for inflammatory bowel disease (recommended levels 250-450). The associated editorial (pg 2-3, N Kerkar) cautions that while “lower levels are sufficient for maintaining biochemical remission…higher levels, similar to that used in IBD, are required for inducing remission.”

My take: Lower doses of azathioprine are likely to maintain biochemical remission and cause fewer side effects.  Metabolite levels can be helpful to assure reasonable levels of 6-TGN and to assure medication adherence.

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Disclaimer: These blog posts are for educational purposes only. Specific dosing of medications (along with potential adverse effects) should be confirmed by prescribing physician.  This content is not a substitute for medical advice, diagnosis or treatment provided by a qualified healthcare provider. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a condition.

Shem Creek, SC

Optimal Dose of Thiopurine When Used for Combination Therapy

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To improve long-term outcomes and response in patients with inflammatory bowel disease, many experts advocate the use of combination therapy (thiopurine with anti-tumor necrosis factor).  Thiopurine cotherapy resulted in higher response rates in pivotal studies (eg. SONIC, UC Success), likely due to lower rates of antidrug antibody (ADA) and higher serum levels of biologic agents (e.g. infliximab).  To achieve these advantages, it is not clear whether a lower dose of a thiopurine may be similarly effective as a higher dose.  If a lower dose could result in a similar effect, it would likely result in fewer adverse effects.

A recent study (Yarur AJ, et al. Clin Gastroenterol Hepatol 2015; 13: 1118-24) provide some data to address the issue of optimal dosing of thiopurines.  The authors performed a cross-sectional study of 72 patients receiving infliximab (IFX) and a thiopurine.

Key findings:

  • The thiopurine metabolite 6-thioguanine (6-TG) that “best predicted a higher level of infliximab was 125 pmol/8 x 10 to the 8th RBCs.”
  • Only 8 patients (11%) had detectable antibodies to infliximab (ATI)
  • Patients with 6-TG <125 were more likely to have ATI (OR 1.3)
  • Higher 6-TG levels did not confer additional benefit

This study had many limitations including the small number of patients and the cross sectional design.  In addition, the patients may not be representative of typical patients; more than 50% were in endoscopic remission. A randomized controlled trial with larger number of patients is needed for a more definitive answer.

Take-home message: (from authors); “6-TGN metabolite levels rather than weight-based dosing may assist clinicians in optimizing treatment when using thiopurines in combination with IFX…lower target 6-TGN levels (125-176 pmol/8 x 10 to the 8th RBCs) may be adequate to maximize IFX levels and reduce immunogenicity while potentially minimizing toxicity.”

Briefly noted:

Ananthakrishnan AN et al. Clin Gastroenterol Hepatol 2015; 13: 1197-1200.  In this prospective study with 1659 patients with Crohn’s disease (CD) and 946 patients with ulcerative colitis, the authors found wide variation among the 7 participating academic centers, particularly with regard to CD treatment.  Comparing the site with the lowest usage to the highest usage, for CD:

  • Oral mesalamine 13% vs. 46%
  • Immunomodulator use 16% vs. 56%
  • Anti-TNF use 31% vs 60%
  • Combination therapy 8% vs 32%
  • Immunomodulator-naive anti-TNF use 10% vs. 17%
  • Surgery 32% vs 55%

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