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Background: Pretherapeutic screening for dihydropyrimidine dehydrogenase (DPD) deficiency is recommended prior to the administration of fluoropyrimidine-based chemotherapy. However, the best strategy to identify DPD deficiency in End Stage Renal Disease (ESRD) patients is unknown.Methods: We assessed the characteristics of both DPD phenotypes and DPYD genotypes in 20 dialyzed patients before and after dialysis session. The extent to which the concentrations of uracil [U] and dihydrouracil [UH2] were affected by dialysis was evaluated.Results: Mean [U] was 14 ± 3.3 ng/ml before the dialysis session, and 7.9 ± 2.7 ng/ml after. Notably, mean [U] in 119 non-ESRD patients during the same timeline was 8.7 ± 3.9 ng/ml, which is similar to [U] values after dialysis session (p = 0.38). [U] values > 16 ng/ml were measured in 4 ESRD patients (20%), whereas the rate was 3.3% in the non-ESRD cohort. Whole gene sequencing did not reveal DPYD deleterious allelic variants in the 4 ESRD patients with [U] values > 16 ng/ml. The profile of [UH2] values during dialysis was similar to that of [U]: 385 ± 86 ng/ml before, and 185 ± 62 ng/ml after (mean reduction rate 42.5%). Thus, [UH2]:[U] ratio remained unaffected by dialysis, and was similar to the values in non-ESRD patients (22.4 ± 7.1).Conclusion: Phenotyping based on measuring plasma [U] before a dialysis sessions in ESRD patients is associated with an unacceptable high rate of false positives. The optimal strategy for the identification of patients with DPD deficiency in this population would be the monitor the [UH2]:[U] ratio, which remains unaffected. [ABSTRACT FROM AUTHOR]

Purpose: The pharmacokinetics (PK) of carfilzomib have been previously studied in multiple myeloma patients with varying degrees of renal impairment (normal, mild, moderate, severe, and end-stage renal disease [ESRD]) at doses of 15 and 20 mg/m2. This study evaluated carfilzomib PK at higher doses of 27 and 56 mg/m2 in normal renal function and ESRD patients.Methods: Patients received carfilzomib on two consecutive days/week for 3 weeks every 28-day cycle: 20 mg/m2 (cycle 1 day 1-2), escalated to 27 mg/m2 on cycle 1 day 8; if tolerated, 56 mg/m2 starting cycle 2 day 1. The primary objective was PK assessment with safety/tolerability and response rate as secondary and exploratory objectives, respectively.Results: 26 patients were enrolled (15 normal, 11 ESRD). There was a trend toward higher area under the concentration time curve (AUC) and maximum concentration in ESRD versus normal renal function patients; however, high interpatient PK variability was discerned. Relative to patients with normal renal function, ESRD patients showed 33% higher AUC. Overall response rate was 43% for the normal renal function and 60% for the ESRD groups. Safety findings were generally similar between the two groups and consistent with the known safety profile of carfilzomib in multiple myeloma patients.Conclusion: There were no meaningful differences in PK between patients with normal renal function and ESRD in light of carfilzomib exposure-response relationships. These results continue to support dosing recommendation that no starting dose adjustment of carfilzomib appears warranted in patients with baseline renal impairment. [ABSTRACT FROM AUTHOR]