Review for 10.1186/s12876-022-02439-y (2022)

Reviewer’s report
Title: 
Subcutaneous administration, higher age and lower renal function are associated with erythrocyte
methotrexate accumulation in Crohn’s disease: a cross-sectional study
Version: 
0 
Date: 
11 Apr 2022
Reviewer's report:
In their manuscript entitled "Subcutaneous administration, higher age and lower renal function are
associated with intracellular methotrexate accumulation in Crohn's disease: a cross-sectional study" van
de Meeberg and colleagues report on a cross-sectional monocenter trial in which MTX metabolites were
measured in erythrocytes of patients with Crohn's disease. Briefly, they report that concentrations of MTX
polyglutamates were quite heterogeneous in a cohort of 19 patients. However, they were able to
demonstrate associations with mode of application (s.c. vs. oral), age and kidney function. These results
confirm previous findings in other inflammatory disorders such as rheumatoid arthritis. The manuscript is
well written and the experiments are well performed and well described. A major limitation is the rather
small sample size and the amoint of data presented within this manuscript is therefore somewhat limited. 
As discussed by the authors, the small cohort size may be a source for bias and hampered more in depth
analysis such as analysis of genetic polymorphisms which were previously shown to affect MTX
metabolism. However, the reported variability questions the use of MTX-polyglutamate measurements to
guide personalized medicine-approaches, at least in patients with Crohn's and is therefore worth reporting.
I have just some minor comments:
The authors excluded one patient for suspected non-adherence to MTX intake. How do the authors
confirm that the remaining patients were adherent to MTX therapy?
The amount of data presented within Figures 1 and 2 is limited, both should be combined.
I have doubts whether it makes sense to do a multivariable regression analysis on 18 patients. Please
discuss.
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