Determinants of the elimination of methotrexate and 7-hydroxy-methotrexate following high-dose infusional therapy to cancer patients

Abstract

Aims: To characterize determinants of the elimination of methotrexate (MTX) and 7-hydroxy-methotrexate (7-OH-MTX) in patients receiving high-dose MTX therapy (HDMTX).

Methods: 24 and 48-h blood samples from 76 patients receiving HDMTX (dose range 300 mg m-2 to 12 g m-2) were analysed, and concentration-time data were subjected to population pharmacokinetic and covariate analysis using nonlinear mixed-effect modelling (NONMEM).

Results: Treatment-related mortality was 1.3% (one patient with renal failure). Values for MTX clearance (CLMTX) and 7-OH-MTX clearance (CL7-OH-MTX) were estimated at 8.85 and 2 L-1, respectively. Baseline creatinine clearance correlated with CLMTX and CL7-OH-MTX. Concurrent administration of benzimidazoles led to a 27% decrease in CLMTX and a 39% decrease in CL7-OH-MTX. Prior administration of nonsteroidal anti-inflammatory drugs (NSAIDs) resulted in a 16% decrease in CLMTX and a 38% decrease in CL7-OH-MTX. Plasma MTX concentrations were significantly higher in patients also receiving benzimidazoles at 24 h (2.01 micromol L-1vs. 0.66 micromol L-1, P<10(-4)) and at 48 h (0.25 micromol L-1vs. 0.12 micromol L-1, P<10(-4)). 7-OH-MTX plasma concentrations were also significantly higher in patients with concurrent benzimidazoles as compared with patients without benzimidazoles at 24 h (4.47 micromol L-1vs. 2.52 micromol L-1, P=0.0009) and at 48 h (1.11 micromol L-1vs. 0.72 micromol L-1, P=0.031).

Conclusions: In patients receiving HDMTX, concurrent administration of benzimidazoles was associated with a significant decrease of CLMTX and CL7-OH-MTX, resulting in significantly higher plasma concentrations of MTX and 7-OH-MTX. The data suggest that benzimidazole treatment should be seen as a relative contraindication for HDMTX.

Figure 1

Mean MTX plasma concentration time profiles and those of the two most extreme outliers (patients 36 and 63), both of whom received 3 mg MTX as a 3 h infusion. ID-36 (▴); ID-63 (▪); mean curve (—)

Figure 2

Five compartment model for MTX and 7-OH-MTX pharmacokinetics; CL = clearance, Q = intercompartmental clearance

Figure 3

Goodness-of-fit plots from the final population pharmacokinetic model (all data are log-transformed). (A) Observed vs. predicted MTX concentrations. (B) Observed vs. individual Bayesian predicted MTX concentrations. (C) Observed vs. the model predicted 7-OH-MTX concentrations. (D) Observed vs. individual Bayesian predicted of 7-OH-MTX concentrations.