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Subcutaneous administration, higher age and lower renal function are associated with erythrocyte methotrexate
M M van de Meeberg1,2, M L Seinen3, H H Fidder4
1Department of Gastroenterology and Hepatology, University Medical Centre Utrecht, Utrecht, The Netherlands. m.vandemeeberg@amsterdamumc.nl.
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 (β = 0.71) and lower estimated glomerular filtration rate (β = - 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.
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