Oral versus parenteral administration of methotrexate for the treatment of active RA

Methotrexate polyglutamates as a potential marker of adherence to long-term therapy in children with juvenile idiopathic arthritis and juvenile dermatomyositis: an observational, cross-sectional study

Introduction

Methotrexate (MTX) is a cornerstone of treatment in a wide variety of inflammatory conditions, including juvenile idiopathic arthritis (JIA) and juvenile dermatomyositis (JDM). However, owing to its narrow therapeutic index and the considerable interpatient variability in clinical response, monitoring of adherence to MTX is important. The present study demonstrates the feasibility of using methotrexate polyglutamates (MTXPGs) as a biomarker to measure adherence to MTX treatment in children with JIA and JDM.

Methods

Data were collected prospectively from a cohort of 48 children (median age 11.5 years) who received oral or subcutaneous (SC) MTX therapy for JIA or JDM. Dried blood spot samples were obtained from children by finger pick at the clinic or via self- or parent-led sampling at home, and they were analysed to determine the variability in MTXPG concentrations and assess adherence to MTX therapy.

Results

Wide fluctuations in MTXPG total concentrations (>2.0-fold variations) were found in 17 patients receiving stable weekly doses of MTX, which is indicative of nonadherence or partial adherence to MTX therapy. Age (P = 0.026) and route of administration (P = 0.005) were the most important predictors of nonadherence to MTX treatment. In addition, the study showed that MTX dose and route of administration were significantly associated with variations in the distribution of MTXPG subtypes. Higher doses and SC administration of MTX produced higher levels of total MTXPGs and selective accumulation of longer-chain MTXPGs (P < 0.001 and P < 0.0001, respectively).

Conclusions

Nonadherence to MTX therapy is a significant problem in children with JIA and JDM. The present study suggests that patients with inadequate adherence and/or intolerance to oral MTX may benefit from SC administration of the drug. The clinical utility of MTXPG levels to monitor and optimise adherence to MTX in children has been demonstrated.

Trial registration

ISRCTN Registry identifier: ISRCTN93945409. Registered 2 December 2011.

Red blood cell methotrexate polyglutamates emerge as a function of dosage intensity and route of administration during pulse methotrexate therapy in rheumatoid arthritis

OBJECTIVE

MTX is a prodrug producing anti-arthritic effects through a folylpolyglutamate synthase-mediated activation to MTX polyglutamates (MTXPGs). Our objective was to characterize the pharmacokinetics of intracellular MTXPGs and the factors associated with their accumulation in adult RA patients treated with MTX weekly.

METHODS

MTX pharmacokinetics were evaluated in 47 MTX-naïve patients enrolled in an MTX dose-escalation study for an average of 20 weeks and 223 patients enrolled in a cross-sectional study under long-term MTX therapy. Short-chain (MTXPG1-2), long-chain (MTXPG3) and very long-chain (MTXPG4-5) concentrations were measured in circulating red blood cells using liquid chromatography. Statistical analyses consisted of non-linear mixed models, multivariate regression analyses and Wilcoxon signed-rank test.

RESULTS

The accumulation of MTXPG1-5 was sigmoidal and steady-state concentrations were achieved after 7 weeks of therapy. However, additional exposure and MTX dosage escalation produced a selective redistribution towards longer chain MTXPGs at the expense of shorter chain MTXPGs. Age, glomerular filtration rate and route of MTX administration were the most important predictors of MTXPG accumulation. In 10 patients, a switch from oral to parenteral MTX was associated with a 37% increase in long-chain MTXPGs, a 132% increase in very long-chain MTXPGs and a concomitant 31% reduction in disease activity (P<0.02).

CONCLUSION

The selective emergence of long-chain MTXPGs is function of dose, time of exposure and hence dosage intensity. Switching from oral to parenteral MTX produces a selective accumulation of longer chain MTXPGs that are known to be more potent inhibitors of de novo purine biosynthesis than shorter chain MTXPGs.