Subcutaneous administration, higher age and lower renal function are associated with erythrocyte methotrexate accumulation in Crohn's disease: a cross-sectional study.

BACKGROUND: Methotrexate is an immunomodulatory drug for patients with Crohn's disease. Erythrocyte MTX-polyglutamates (MTX-PG1-5) may be used for therapeutic drug monitoring (TDM) as MTX-PG is thought to mediate MTX's efficacy. Information on determinants of the concentration of MTX-PG in patients with Crohn's disease is lacking. We aim to identify clinical and biochemical determinants of the erythrocyte MTX-PG1-5 and MTX-PGtotal concentration in patients with Crohn's disease. METHODS: Adults with Crohn's disease on methotrexate treatment who visited the outpatient clinic of Amsterdam UMC were included. Erythrocyte MTX-PGs were measured by tandem mass spectrometry. RESULTS: Nineteen patients were included, with a median duration of MTX use of 77 months (range 7-202). Twelve patients received MTX monotherapy, whereas 7 patients were on concomitant TNF-α inhibitors. The mean dose of MTX was 15.5 mg (SD ± 2.8) and 12 (63%) patients used subcutaneous MTX. MTX-PG1-5 were successfully measured in 18 patients, showing substantial variability in concentrations of MTX-PGtotal and individual species. The median MTX-PGtotal was 117.1 nmol/L (range 46.4-258.7) with preferential accumulation of MTX-PG3 (43.1 nmol/L, range 15.3-96.1). Patients on subcutaneous compared to oral MTX had higher median MTX-PG(4,5) levels (55 versus 9 nmol/L, p = 0.01). Higher age (ß = 0.71) and lower estimated glomerular filtration rate (ß = - 0.52) were associated with a significantly higher MTX-PGtotal concentration (R2 = 0.60, p = 0.001). CONCLUSION: MTX-PG concentrations display a considerable inter-individual variability. Higher MTX-PG accumulation is associated with subcutaneous administration, higher age, and lower renal function in Crohn's disease patients.

The pharmacokinetic effect of adalimumab on thiopurine metabolism in Crohn's disease patients.

BACKGROUND AND AIMS: A drug interaction between infliximab and azathioprine has previously been reported in Crohn's disease patients: the concentration of the main active thiopurine metabolites, the 6-thioguanine nucleotides (6-TGN), increased 1-3 weeks after the first infliximab infusion by 50% compared to baseline. The aim of this prospective study was to determine the effect of adalimumab on thiopurine metabolism in Crohn's disease patients, evaluated by 6-TGN and 6-methylmercaptopurine ribonucleotides (6-MMPR) concentration measurement. METHODS: Crohn's disease patients on azathioprine or mercaptopurine maintenance therapy starting with concomitant adalimumab treatment were included. 6-TGN and 6-MMPR concentrations were determined before initiation of adalimumab and after 2, 4, 6 and 12 weeks of combination therapy. The activity of three essential enzymes involving thiopurine metabolism, thiopurine S-methyltransferase (TPMT), hypoxanthine-guanine phosphoribosyl transferase (HGPRT) and inosine-triphosphate pyrophosphatase (ITPase), was evaluated at baseline and week 4. Clinical outcome was evaluated by the Crohn's disease activity index and C-reactive protein concentrations at baseline, week 4 and week 12. RESULTS: Twelve Crohn's disease patients were analyzed. During the follow-up period of 12 weeks the median 6-TGN and 6-MMPR concentrations did not significantly change compared to baseline. TPMT, ITPase and HGPRT enzyme activity did not change either after 4 weeks. In two patients (17%) myelotoxicity was observed within 2-4 weeks, in whom both low therapeutic 6-TGN and 6-MMPR concentrations were found. CONCLUSIONS: In this study in Crohn's disease patients no pharmacokinetic interaction was shown between adalimumab and the conventional thiopurines, azathioprine and mercaptopurine.

The effect of allopurinol and low-dose thiopurine combination therapy on the activity of three pivotal thiopurine metabolizing enzymes: results from a prospective pharmacological study.

INTRODUCTION: Thiopurine therapy is often discontinued in inflammatory bowel disease (IBD) patients. The xanthine oxidase (XO) inhibitor allopurinol has previously shown to enhance thiopurine efficacy and to prevent adverse reactions, the mechanism of this beneficial interaction is not completely clarified. The aim of this study is to observe possible effects of allopurinol and low-dose thiopurine combination therapy on the activity of three pivotal thiopurine metabolizing enzymes. METHODS: A prospective study of IBD patients failing thiopurine therapy due to a skewed thiopurine metabolism was performed. Patients were treated with allopurinol and azathioprine or mercaptopurine. Xanthine oxidase, hypoxanthine-guanine phosphoribosyl transferase (HGPRT) and thiopurine S-methyl transferase (TPMT) activities, and thiopurine metabolites concentrations were measured during thiopurine monotherapy, and after 4 and 12 weeks of combination therapy. RESULTS: Of fifteen IBD patients, XO activity decreased from 0.18 (IQR 0.08-0.3) during thiopurine monotherapy to 0.14 (IQR 0.06-0.2) and 0.11 (IQR 0.06-0.2; p=0.008) mU/hour/ml at 4 and 12 weeks, respectively. HGPRT activity increased from 150 (IQR 114-176) to 180 (IQR 135-213) and 204 nmol/(h×mg protein) (IQR 173-213; p=0.013). TPMT activity seemed not to be affected. 6-Thioguanine nucleotide concentrations increased from 138 (IQR 119-188) to 235 (223-304) and to 265 pmol/8×10^8 (IQR 188-344), whereas 6-methyl mercaptopurine ribonucleotides concentrations decreased from 13230 (IQR 7130-17420) to 690 (IQR 378-1325) and 540 (IQR 240-790) pmol/8×10^8 at 4 and 12 weeks of combination therapy (both p<0.001). CONCLUSION: Allopurinol and thiopurine combination-therapy seems to increase HGPRT and decrease XO activity in IBD patients, which at least in part may explain the observed changes in thiopurine metabolite concentrations.

Thiopurine therapy in inflammatory bowel disease patients: analyses of two 8-year intercept cohorts.

BACKGROUND: Thiopurines have proven efficacy in long-term maintenance therapy of inflammatory bowel disease (IBD). Limited data are available with regard to factors predicting effectiveness and failure of long-term thiopurine use in IBD patients. METHODS: The data in this retrospective study are based on an 8-year intercept cohort of previous or present thiopurine-using IBD patients. Both cohorts are assessed by descriptive and statistical analysis aimed at determining thiopurine effectiveness and the variables that are predictive for failure of thiopurine therapy. RESULTS: In all, 363 IBD patients were included (60% female), 63% with Crohn's disease and 33% with ulcerative colitis. Overall, thiopurines were continued in 145/363 (40%) and discontinued in 208/363 (57%) patients. The proportion of patients still using thiopurines at 3, 6, 12, 24, and 60 months was 73%, 69%, 63%, 51%, and 42%, respectively. Patients discontinued thiopurines due to adverse events (39%), refractoriness (16%), and ongoing remission / patient's request (4%). 6-methylmercaptopurine (6-MMP) concentration and 6-MMP/6-thioguanine nucleotides (6-TGN) ratio were significant higher in the failure group. Prolonged continuation of thiopurines was associated with a decreased risk of discontinuation. CONCLUSIONS: Azathioprine and 6-mercaptopurine were considered effective in approximately 40% of IBD patients after 5 years of treatment. A quarter of the patients discontinued thiopurines within 3 months, mostly due to adverse events. A high 6-MMP concentration or 6-MMP/6-TGN ratio was associated with therapeutic failure. If thiopurine use was successfully initiated in the first months, its use was usually extended over many years, as long-term use was associated with continuation of therapy.