Methotrexate (MTX) is used in high doses in the treatment of cancers such as NHLs, leukemias and osteosarcoma. In some patients it produces renal damage which delays its elimination from the body. Prolonged exposure to high concentrations of MTX results in serious toxic effects. Glucarpidase (Voraxaze™, formerly carboxypeptidase G2) contains a recombinant enzyme which rapidly and predictably breaks down MTX in the blood within 15 minutes of administration. Multiple studies to date have evaluated glucarpidase as an intervention for patients at risk or experiencing toxicities related to MTX overexposure. Continuing studies seek to evaluate the use of glucarpidase in a planned way to circumvent toxicity and prevent prolonged hospitalization. The current study examined the pharmacokinetics of glucarpidase in subjects who had both normal and severely impaired renal function, similar to that of the intended patient population.

Methods: Twelve male and female subjects participated in this study; 8 with normal renal function (calculated creatinine clearance >80 mL/min) and 4 with severely impaired renal function (calculated creatinine clearance <30 mL/min). Each subject received a single intravenous dose of glucarpidase 50 units/kg (equivalent to 114.5 μg/kg), infused over 5 min. Serum glucarpidase profiles were evaluated for all subjects using 7 mL blood samples collected at the following time points: pre-dose (prior to start of glucarpidase IV dose), end of 5-minute infusion, and 0.25, 0.5, 1, 2, 4, 6, 8, 12, 18, 24, 48, 72, and 96 hours following the start of the infusion. The study protocol was approved by the Crescent City Institutional Review Board IRB (New Orleans, LA) and all subjects gave their written informed consent prior to inclusion in the study.

Results: The mean (SD) Cmax for glucarpidase in renally impaired subjects was 2.9 μg/mL (0.83), the mean half-life was 10.0 (2.1) h and mean AUC0-∞ was 24.5(9.4) μg.h/mL. Similar values were found in subjects with normal renal function (mean Cmax 3.1 μg/mL, mean t1/2 9.0 h and mean AUC0-∞ 23.4 μg.h/mL). No adverse events were recorded in the study.

Conclusions: The results indicated little effect of renal impairment on the serum pharmacokinetics of glucarpidase. Evaluations of adverse events, clinical laboratory assessments, vital signs, ECGs, and physical examinations indicated that a single 50 unit/kg dose of glucarpidase was safe and well-tolerated when administered to subjects with normal renal function and subjects with severe renal impairment. PK parameters found in this study may be relevant to cancer patients treated with 50 units/kg glucarpidase, including those with MTX-induced renal toxicity.

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