Time to incorporate preemptive NUDT15 testing before starting thiopurines in inflammatory bowel disease in Asia and beyond: a review

Proactive pharmacogenomics in azathioprine-treated pediatric inflammatory bowel disease at a Chinese tertiary hospital

Background

Despite the emergence of numerous innovative targeted therapies for the management of pediatric inflammatory bowel disease (IBD), azathioprine continues to be a pivotal first-line therapeutic agent. Nonetheless, the considerable frequency of myelosuppression associated with its use warrants careful consideration and further investigation. This study aims to investigate the application of pharmacogenomics in Chinese pediatric IBD treated with azathioprine, and to elucidate its association with the occurrence of myelosuppression.

Methods

We conducted a retrospective analysis to determine the prevalence of pharmacogenetic abnormalities and thiopurine-induced myelosuppression in Chinese pediatric patients with IBD.

Results

Among the 227 patients underwent pharmacogenetic testing, abnormal genetypes occurred in 66 patients, among which 7 patients exhibited aberrant TPMT and 59 had aberrant NUDT15. Of the 58 patients who were treated with azathioprine, 23 cases experienced myelosuppression. All three children with heterozygous mutations in NUDT15 developed leukopenia following azathioprine treatment. Among patients with normal pharmacogenetic results, 20 cases (36.4%) developed myelosuppression, while 35 cases (63.6%) did not. The dose of azathioprine was below the recommended level in guidelines. The mean dose of azathioprine (mg/kg/day) in the myelosuppression group was 1.22 ± 0.32, compared to 1.42 ± 0.42 in the non-myelosuppression group, which represented a statistically significant difference (p < 0.05). Age, gender, and the use of concomitant biologics, mesalazine, or glucocorticoids did not show significant differences between the groups (p > 0.05).

Conclusion

NUDT15 C415T is prevalent in China and is associated with an increased risk of azathioprine-induced myelosuppression. A reduced dose of azathioprine should be considered for Chinese pediatric patients with IBD, even in those with normal pharmacogenetic profiles.

Effectiveness and safety of thiopurines in inflammatory bowel disease patients with NUDT15 polymorphism: a real-world retrospective study

BACKGROUND

Thiopurine S-methyltransferase (TPMT) and Nudix hydrolase (NUDT15) polymorphisms predispose to thiopurine-related leukopenia.

METHODS

Retrospective evaluation of inflammatory bowel disease (IBD) patients harboring NUDT15 polymorphisms and exposed to thiopurines. We report the frequency of NUDT15 polymorphism, frequency of leukopenia, the tolerated dose of azathioprine, and the clinical efficacy of thiopurines.

RESULTS

Of 1440 patients, 118 (8.2%) had NUDT15 polymorphism. Among 51 with complete details, 46 were heterozygous (90.2%), and 5 homozygous (9.2%) for NUDT15. Twenty (43.5%) heterozygous and all homozygous patients developed leukopenia. Leukopenia was significantly more in NUDT15 heterozygous group compared to controls (43.45% vs 7.8%, Odds ratio: 9, 95% CI 3.57-22.9). The maximum tolerated dose of azathioprine was lower in NUDT15 heterozygous group (1.1 ± 0.4 mg per kg vs 1.7 ± 0.7 mg per kg, p = 0.002). The mean time to leukopenia was earlier in the heterozygous group vs controls (19 ± 56 weeks vs 70 ± 53 weeks, p-value 0.002). Seven (35%) of 20 heterozygous patients who developed leukopenia, could be maintained at a lower dose of thiopurine. Twenty-five maintained clinical remission while on thiopurines.

CONCLUSION

Thiopurines should be avoided in NUDT15 homozygous but can be used cautiously at lower dosages with frequent monitoring among heterozygous patients.

Effects of genetic and clinical factors on thiopurine drugs pharmacokinetics in Tunisian patients

Aim: Thiopurine drugs are used in the treatment of various diseases including inflammatory bowel disease. Thiopurine-S-methyltransferase (TPMT) and inosine triphosphate pyrophosphatase (ITPA) are the crucial enzymes involved in thiopurines metabolism. The present study aims to investigate in Tunisian patients, the influence of genetic and nongenetic factors on thiopurine drugs pharmacokinetics.Experimental approach: We have included patients having received thiopurine drugs and have undergone 6-thioguanine nucleotides (6-TGN) concentration monitoring. The identification of TPMT and ITPA polymorphisms was performed using the polymerase chain reaction-restriction fragment length polymorphism method. The impact of both genetic and nongenetic factors on the variability of the 6-TGN C/D ratio was analyzed through a stepwise multiple regression model.Key results: One hundred and twenty-three patients were included in the study. For TPMT, the most frequent variant allele was TPMT*3B (3.3%). For ITPA, the predominant polymorphism was the c.IVS2 + 21A> C (7%). We have demonstrated that only gender, the TPMT*3A and TPMT*3C alleles are significantly involved on the variability of thiopurines pharmacokinetics.Conclusion: Our study is the first to evaluate, in African patients, the impact of both genetic and nongenetic factors on the thiopurine drugs pharmacokinetics. Considering the narrow therapeutic range of these drugs, TPMT genotyping combined with 6-TGN blood concentration monitoring may enhance their efficacy and safety.

Adverse Event Profiles of Adalimumab in Children: A Disproportionality Analysis

BACKGROUND

Adalimumab has been approved by the U.S. Food and Drug Administration (FDA) for the treatment of adult rheumatoid arthritis (RA), and subsequently approved for pediatric treatment of various autoimmune diseases in children of different ages. Due to genetic differences between children and adults in terms of physiology and immunity, there is a need to explore the safety of adalimumab in children in the real world. The aim of this study is to identify potential adverse event (AE) signals associated with the use of adalimumab in pediatric patients (<18 years old) using data from the FDA Adverse Event Reporting System (FAERS).

METHODS

AEs associated with adalimumab in pediatric patients reported in the FAERS database from the first quarter (Q1) of 2017 to the third quarter (Q3) of 2022 were systematically gathered. Reporting odds ratio (ROR), the proportional reporting ratio (PRR), the information component (IC), and the empirical Bayes geometric mean (EBGM) were used to assess the relationship between adalimumab and AEs in children.

RESULTS

Out of 8,363,304 reports collected from the FAERS database during the study period, 3819 reports on children on adalimumab were identified. Adalimumab-related AEs reports were concentrated on 10 toxicity areas and a total of 202 positive signals were detected, of which injection site papule (ROR = 261.97) and intestinal fistula (ROR = 122.09) had the strongest signals. Unexpected significant AEs, including intestinal obstruction, immunodeficiency, abdominal abscess, and Takayasu's arteritis might also occur. In comparison with patients of all ages in the same time window, the median onset time of children was shorter (99 vs. 149 days). Most of the AE cases occurred in children within the first 1 (1.71%), 2 (8.12%), and 3 months (8.39%) and had early failure types after adalimumab initiation. Methotrexate, folic acid, prednisone, azathioprine, and mesalamine were the top five drugs used concomitantly for adalimumab-associated AEs.

CONCLUSIONS

When adalimumab is used in children, especially in the first 3 months of treatment, in addition to the AEs recorded in the drug package insert, close attention should be paid to the new potential AEs off-label to ensure the safety of adalimumab in children.

Uphill battle: Innovation of thiopurine therapy in global inflammatory bowel disease care

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder of the gastrointestinal tract that encompasses two major conditions: Crohn's disease (CD) and ulcerative colitis (UC). Historically, IBD has been primarily reported in western countries, but over the past decades, its prevalence is rapidly increasing, especially in lower and middle-income countries (LMICs) such as India and China and also in Sub-Saharan Africa. The prevalence of IBD in LMICs has been the subject of growing concern due to the impact of access to public healthcare and the burden it places on healthcare resources. The classical thiopurines face significant challenges due to cessation of therapy in approximately half of patients within one year due to side effects or ineffectiveness. In this article, we highlight innovating thiopurine treatment for IBD patients in downregulating side effects and improving efficacy.

Therapeutic drug monitoring in inflammatory bowel disease: A practical approach

The global burden of inflammatory bowel diseases (IBD) is estimated at 4.9 million and the global prevalence exceeds 0.3%. Multiple newer therapeutic agents have broadened the options for the therapy of IBD in the last three decades. Thiopurines, however, have retained their place as maintenance therapy in IBD, especially in resource-constrained setting. But thiopurines have narrow therapeutic range, often needing discontinuation due to side effects or lack of efficacy. Biologic agents revolutionized the treatment of IBD, but the efficacy is lost in 50% of patient after one year. These outcomes are often due to inadequate drug concentrations that may lead to the development of antibodies as well as pharmacodynamic failure. Therapeutic drug monitoring (TDM) was proposed to reduce loss of response and to optimize the therapy in patients on thiopurine and biologic therapy. TDM is based on exposure-response relationship, suggesting a positive correlation between elevated serum anti-TNF concentrations and favorable therapeutic outcomes. TDM has multiple facets. This article discusses the benefits, evidence and limitations of TDM. The practical use of TDM in clinical practice is highlighted. Newer developments in the field and their relevance in practice are discussed.

Risk-stratified monitoring for thiopurine toxicity in immune-mediated inflammatory diseases: prognostic model development, validation, and, health economic evaluation

Background

Patients established on thiopurines (e.g., azathioprine) are recommended to undergo three-monthly blood tests for the early detection of blood, liver, or kidney toxicity. These side-effects are uncommon during long-term treatment. We developed a prognostic model that could be used to inform risk-stratified decisions on frequency of monitoring blood-tests during long-term thiopurine treatment, and, performed health-economic evaluation of alternate monitoring intervals.

Methods

This was a retrospective cohort study set in the UK primary-care. Data from the Clinical Practice Research Datalink Aurum and Gold formed development and validation cohorts, respectively. People age ≥18 years, diagnosed with an immune mediated inflammatory disease, prescribed thiopurine by their general practitioner for at-least six-months between January 1, 2007 and December 31, 2019 were eligible. The outcome was thiopurine discontinuation with abnormal blood-test results. Patients were followed up from six-months after first primary-care thiopurine prescription to up to five-years. Penalised Cox regression developed the risk equation. Multiple imputation handled missing predictor data. Calibration and discrimination assessed model performance. A mathematical model evaluated costs and quality-adjusted life years associated with lengthening the interval between blood-tests.

Findings

Data from 5982 (405 events over 16,117 person-years) and 3573 (269 events over 9075 person-years) participants were included in the development and validation cohorts, respectively. Fourteen candidate predictors (21 parameters) were included. The optimism adjusted R2 and Royston D statistic in development data were 0.11 and 0.76, respectively. The calibration slope and Royston D statistic (95% Confidence Interval) in the validation data were 1.10 (0.84-1.36) and 0.72 (0.52-0.92), respectively. A 2-year period between monitoring blood-test was most cost-effective in all deciles of predicted risk but the gain between monitoring annually or biennially reduced in higher risk deciles.

Interpretation

This prognostic model requires information that is readily available during routine clinical care and may be used to risk-stratify blood-test monitoring for thiopurine toxicity. These findings should be considered by specialist societies when recommending blood monitoring during thiopurine prescription to bring about sustainable and equitable change in clinical practice.

Funding

National Institute for Health and Care Research.