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Mechanism of Action
Pralatrexate is a folate analog metabolic inhibitor that competitively inhibits dihydrofolate reductase. It is also a competitive inhibitor for polyglutamylation by the enzyme folylpolyglutamyl synthetase. This inhibition results in the depletion of thymidine and other biological molecules the synthesis of which depends on single carbon transfer.
Pharmacokinetics
Absorption
The pharmacokinetics of pralatrexate administered as a single agent at a dose of 30 mg/m2 administered as an intravenous push over 3-5 minutes once weekly for 6 weeks in 7-week cycles have been eva luated in 10 patients with PTCL. The total systemic clearance of pralatrexate diastereomers was 417 mL/min (S-diastereomer) and 191 mL/min (R-diastereomer). The terminal elimination half-life of pralatrexate was 12-18 hours (coefficient of variance [CV] = 62-120%). Pralatrexate total systemic exposure (AUC) and maximum plasma concentration (Cmax) increased proportionally with dose (dose range 30-325 mg/m2, including pharmacokinetics data from high-dose solid tumor clinical studies). The pharmacokinetics of pralatrexate did not change significantly over multiple treatment cycles, and no accumulation of pralatrexate was observed.
Distribution
Pralatrexate diastereomers showed a steady-state volume of distribution of 105 L (S-diastereomer) and 37 L (R-diastereomer). In vitro studies indicate that pralatrexate is approximately 67% bound to plasma proteins.
Metabolism
In vitro studies using human hepatocytes, liver microsomes and S9 fractions, and recombinant human CYP450 isozymes showed that pralatrexate is not significantly metabolized by the phase I hepatic CYP450 isozymes or phase II hepatic glucuronidases.
Excretion
A mass balance study has not been performed. The mean fraction of unchanged pralatrexate diastereomers excreted in urine following a pralatrexate dose of 30 mg/m2 administered as an intravenous push over 3-5 minutes was 31% (S-diastereomer) (CV = 47%) and 38% (R-diastereomer) (CV = 45%), respectively.
Patients with Renal Impairment
Approximately 34% of pralatrexate was excreted unchanged into urine following a single dose of 30 mg/m2 administered as an intravenous push over 3-5 minutes. In a population pharmacokinetic analysis drug clearance decreased with decreasing creatinine clearance [see Use in Specific Populations (8.7)].
Patients with Hepatic Impairment
Pralatrexate has not been studied in patients with hepatic impairment.
Effects of Age and Gender
Due to the contribution of renal excretion to overall clearance of pralatrexate, age-related decline in renal function may lead to a reduction in clearance and a commensurate increase in plasma exposure. There was no significant effect of gender on pharmacokinetics.
Drug Interactions
In vitro studies indicated that pralatrexate does not induce or inhibit the activity of CYP450 isozymes at concentrations of pralatrexate that can be reasonably expected clinically.
In vitro, pralatrexate is a substrate for the breast cancer resistance protein (BCRP), MRP2, multidrug resistance-associated protein 3 (MRP3), and organic anion transport protein 1B3 (OATP1B3) transporter systems at concentrations of pralatrexate that can be reasonably expected clinically. Pralatrexate is not a substrate of the P glycoprotein (P-gp), organic anion transport protein 1B1 (OATP1B1), organic cation transporter 2 (OCT2), organic anion transporter 1 (OAT1), |
