<p>Niraparib is an inhibitor of poly (ADP-ribose) polymerase (PARP) enzymes, PARP-1 and PARP-2, which play a role in DNA repair. In vitro studies have shown that niraparib induced cytotoxicity may involve inhibition of PARP enzymatic activity and increased formation of PARP-DNA complexes resulting in DNA damage, apoptosis and cell death. Increased Niraparib-induced cytotoxicity was observed in tumor cell lines with or without deficiencies in BRCA1/2. Niraparib decreased tumor growth in mouse xenograft models of human cancer cell lines with deficiencies in BRCA1/2 and in human patient-derived xenograft tumor models with homologous recombination deficiency that had either mutated or wild type BRCA1/2.<br />
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<strong>Absorption</strong>: The absolute bioavailability of niraparib is approximately 73%. Following oral administration of Niraparib, peak plasma concentration, Cmax, is reached within 3 hours. Concomitant administration of a high fat meal (800-1,000 calories with approximately 50% of total caloric content of the meal from fat) did not significantly affect the pharmacokinetics of Niraparib.<br />
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<strong>Distribution</strong>: Niraparib is 83.0% bound to human plasma proteins. The average (&plusmn;SD) apparent volume of distribution (Vd/F) was 1220 (&plusmn;1114) L. In a population pharmacokinetic analysis, the Vd/F of Niraparib was 1074 L in cancer patients.<br />
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<strong>Elimination</strong>: Following multiple daily doses of 300 mg Niraparib, the mean half-life (t1/2) is 36 hours. In a population pharmacokinetic analysis, the apparent total clearance (CL/F) of niraparib was 16.2 L/h in cancer patients.<br />
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<strong>Metabolism</strong>: Niraparib is metabolized primarily by carboxylesterases (CEs) to form a major inactive metabolite, which subsequently undergoes glucuronidation.<br />
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<strong>Excretion</strong>: Following administration of a single oral 300 mg dose of radio-labeled Niraparib, the average percent recovery of the administered dose over 21 days was 47.5% (range 33.4% to 60.2%) in urine and 38.8% (range 28.3% to 47.0%) in feces. In pooled samples collected over 6 days, unchanged Niraparib accounted for 11% and 19% of the administered dose recovered in urine and feces, respectively</p>