Thiopurines’ Metabolites and Drug Toxicity: A Meta-Analysis

Abstract

Many questions remain unanswered regarding therapeutic drug monitoring (TDM) utility with thiopurines. This study aims to establish a relationship between thiopurines’ metabolites and drug toxicity. We performed a systematic review with inclusion of studies evaluating the relationship between thiopurines’ metabolites and drug toxicity. Meta-analysis of mean difference (MD), correlations and odds ratio (OR) was performed. We identified 21,240 records, 72 of which were eligible for meta-analysis. Levels of 6-thioguanine nucleotides (6-TGN) were higher in patients with leukopenia (MD 127.06 pmol/8 × 108 RBC) and gastrointestinal intolerance (MD 201.46 pmol/8 × 108 RBC), and lower in patients with hepatotoxicity (MD −40.6 pmol × 108 RBC). We established a significant correlation between 6-TGN and leukocytes (r = −0.21), neutrophils (r = −0.24) and alanine aminotransferase levels (r = −0.24). OR for leukopenia in patients with elevated 6-TGN was 4.63 (95% CI 2.24; 9.57). An optimal cut-off of 135 pmol/8 × 108 RBC for leukopenia was calculated (sensitivity 75.4%; specificity 46.4%). 6-methylmercaptopurine ribonucleotides (6-MMPR) were significantly associated with hepatotoxicity (MD 3241.2 pmol/8 × 108 RBC; OR 4.28; 95% CI 3.20; 5.71). Levels of 6-MMPR measured in the first 8 weeks of treatment were associated with leukopenia. We conclude that TDM could be used to prevent thiopurines’ toxicity. As optimal metabolites level may vary according to indication, physicians may adapt posology to decrease toxicity without compromising efficacy.