Simultaneous Determination of Unbound Plasma Concentration of Methotrexate and 7-Hydroxymethotrexate in Children Patients Receiving High-Dose Methotrexate Therapy.

BACKGROUND

High-dose methotrexate (HD-MTX) is seen as an effective therapy for acute lymphoblastic leukemia (ALL); however, it is extremely toxic. Monitoring the plasma concentrations of methotrexate (MTX) and its important metabolite, 7-hydroxy-methotrexate (7-OH-MTX), on a routine basis aids in dose modification of rescue medications and in avoiding toxicity. The pharmacologically active and toxic effects of drugs are due to the unbound portion, as most drugs are bound to plasma proteins to some degree. However, the simultaneous measurement of unbound plasma concentrations of MTX and 7-OH-MTX has not been reported.

METHODS

We developed and validated a hollow fiber centrifugal ultrafiltration (HFCF-UF) technology to simultaneously analyze unbound MTX and 7-OH-MTX concentrations in human plasma. In total, 234 plasma samples from 58 children diagnosed with ALL who were administered HD-MTX were used in our study. We investigated the connection between unbound and total plasma concentrations of MTX and 7-OH-MTX, as well as how these concentrations relate to liver and renal function.

RESULTS

The method that was developed is both simple and accurate. A weak linear relationship was observed between the concentrations of unbound and total 7-OH-MTX ( = 0.732). The concentration of total MTX and unbound 7-OH-MTX were both positively correlated with creatinine (Cr) levels and negatively correlated with Creatinine clearance (CCr). There was a wide variation in the concentration ratios of 7-OH-MTX to MTX, both total and unbound, and these ratios were significantly lower in individuals with impaired liver function.

CONCLUSION

The total concentration of 7-OH-MTX is an unreliable predictor of unbound concentration, necessitating the monitoring of unbound levels. The concentration ratios of 7-OH-MTX to MTX (both total and unbound) could be more accurate and sensitive biomarkers for predicting hepatotoxicity.