Understanding hemoglobin contribution to high-dose methotrexate disposition-population pharmacokinetics in pediatric patients with hematological malignancies

PURPOSE

The aim of the present study was to develop a population pharmacokinetic model for methotrexate (MTX) during high-dose treatment (HDMTX) in pediatric patients with acute lymphoblastic leukemia (ALL) and non-Hodgkin's lymphoma (NHL) and to describe the influence of variability factors.

METHODS

The study included 50 patients of both sexes (aged 1-18 years) who received 3 or 5 g/m2 of HDMTX. A nonlinear mixed effect modeling approach was applied for data analysis. Parameter estimation was performed by first-order conditional estimation method with interaction (FOCEI), whereas stepwise covariate modeling was used to assess variability factors.

RESULTS

The final model is a two-compartment model that incorporates the effect of body surface area and the influence of hemoglobin and serum creatinine on MTX clearance (CL). Population pharmacokinetic values for a typical subject were estimated at 5.75 L/h/m2 for clearance (CL), 21.3 L/m2 for volume of the central compartment (V1), 8.2 L/m2 for volume of the peripheral compartment (V2), and 0.087 L/h/m2 for intercompartmental clearance (Q). According to the final model, MTX CL decreases with increasing serum creatinine, whereas a positive effect was captured for hemoglobin. A difference of almost 32% in MTX CL was observed among patients' hemoglobin values reported in the study.

CONCLUSION

The developed population pharmacokinetic model can contribute to the therapy optimization during HDMTX in pediatric patients with ALL and NHL. In addition to renal function and body weight, it describes the influence of hemoglobin on CL, allowing better understanding of its contribution to the disposition of HDMTX.

The Influence of Subclinical Active Inflammation on IFX Pharmacokinetic Modeling and Disease Progression Assessment: Findings from a Prospective Real-World Study in Inflammatory Bowel Disease Patients

BACKGROUND AND AIMS

Effective management of inflammatory bowel disease (IBD) relies on a comprehensive understanding of infliximab (IFX) pharmacokinetics (PK). This study's primary goal was to develop a robust PK model, identifying key covariates influencing IFX clearance (CL), while concurrently evaluating the risk of disease progression during the maintenance phase of IBD treatment.

METHODS

The multicenter, prospective, real-world DIRECT study was conducted in several care centers, which included 369 IBD patients in the maintenance phase of IFX therapy. A two-compartment population PK model was used to determine IFX CL and covariates. Logistic and Cox regressions were applied to elucidate the associations between disease progression and covariates embedded in the PK model.

RESULTS

The PK model included the contributions of weight, albumin, antidrug antibody (ADA), and fecal calprotectin (FC). On average, higher ADA, FC concentration and weight, and lower albumin concentration resulted in higher IFX CL. In the multivariate regression analyses, FC levels influenced the odds of disease progression in the majority of its definitions, when adjusted for several confounding factors. Additionally, alongside FC, both IFX and CL demonstrated a significant impact on the temporal aspect of disease progression.

CONCLUSION

In this 2-year real-world study, readily available clinical covariates, notably FC, significantly impacted IFX availability in IBD patients. We demonstrated that subclinical active inflammation, as mirrored by FC or CRP, substantially influenced IFX clearance. Importantly, FC emerged as a pivotal determinant, not only of IFX pharmacokinetics but also of disease progression. These findings underscore the need to integrate FC into forthcoming IFX pharmacokinetic models, amplifying its clinical significance.

THE POSOLOGY AND TROUGH CONCENTRATIONS OF DIGOXIN IN ADULT AND ELDERLY PATIENTS

Being a narrow therapeutic index drug, digoxin may cause harm if dosed without regular measurements of serum levels. Due to various limitations in its dosing, different challenges still exist in clinical practice. This study aimed to assess digoxin though concentrations after different regimens in adult and elderly patients, and to identify predictor variables for the ratio of given dose and digoxin trough level. This was prospective open-label study. Digoxin was administered per os as 0.125 or 0.25 mg during different continuous and interrupted dosage regimens. Study protocol allowed an additional therapy according to contemporary guidelines. Digoxin concentrations were determined using Abbott AxSYM Digoxin II assay in trough samples (1-3 per patient) after 3-4 weeks stable regimen. In total, 191 concentrations (104 patients) were analyzed. Digoxin weekly dose was in range 0.375-1.75 mg. On average, we observed slightly lower digoxin levels in HF patients. Results showed that in patients receiving digoxin with interrupted dosage regimen post- pause digoxin level was statistically significantly lower than pre-pause (p < 0.05). Based on multi- ple linear regression, the ratio of given dose and trough concentration was mainly predicted by clearance creatinine, and to lesser extent by patient's ideal body weight. Interrupted dosing schedule shows greater variability in drug levels comparing to continuous dosing, and it additionally causes difficulties in reaching and maintaining steady trough levels between doses. Hence, individualization of dosing regimen should be carefully guided based on target levels and not solely on clinical signs and symptoms.