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1286. Pharmacokinetics, Excretion, and Mass Balance of [14C]-Rezafungin Following Intravenous (IV) Administration in Healthy Adults

Abstract Background Rezafungin is a once-weekly novel echinocandin antifungal currently in Phase 3 development for treatment of candidemia and invasive candidiasis (ReSTORE) and for prevention of invasive fungal disease caused by Candida, Aspergillus, and Pneumocystis in blood and marrow transplant recipients (ReSPECT). Nonclinical ADME studies in rats and monkeys show rezafungin is primarily excreted unchanged in feces, with urine as a minor route. This study was conducted to characterize the routes of elimination of [14C]-rezafungin and the pharmacokinetics of total radioactivity and plasma rezafungin in humans. Methods Nine healthy male subjects received a single IV 400-mg rezafungin infusion containing 200 µCi of [14C]-rezafungin. Serial blood samples, urine, and feces were collected at specified times over 60 days; subjects were initially confined in the clinical research unit (CRU) for 17 days postdose and returned for two follow-up visits (days 29 and 60). During the period of time subjects were away from the CRU, recovery of radioactivity was estimated by linear interpolation. Results Rezafungin exhibited a long plasma half-life and was mainly excreted in feces unchanged. Cumulative recovery of radioactivity from excreta collected through the first 17 days was 52% (38% in feces, 14% in urine), reinforcing the slow overall elimination of rezafungin. Overall recovery of the administered dose by day 60 was estimated to be 88.3% (65.6% in feces, 22.7% in urine) (Figure 1). Mean blood/plasma concentration ratios ranged from 0.860 to 1.02 through the last collection time point (day 60), which indicated low association of radioactivity with blood cells. Rezafungin was the predominant compound measured in plasma and feces across all collected time points. In the urine, as observed in rat and monkey metabolite profiling studies, low level, inactive, oxidative metabolites were identified as 2-, 3-, 4-hydroxylpentyl rezafungin, and despentyl-rezafungin Figure 1 Conclusion Results from this human excretion balance, metabolism and PK study are consistent with nonclinical results, which showed fecal excretion as the major route of elimination of rezafungin. Rezafungin was the predominant compound in plasma and feces. Disclosures Voon Ong, PhD, Cidara Therapeutics, Inc. (Employee, Shareholder) Shawn Flanagan, PhD, Cidara Therapeutics, Inc. (Employee, Shareholder) Taylor Sandison, MD, MPH, Cidara Therapeutics, Inc. (Employee, Shareholder)


Session: P-58. Novel Agents
Background. Cefiderocol (CFDC) is the first siderophore cephalosporin approved (US and EU) for a broad range of infections caused by Gram-negative (GN) bacteria, including carbapenem-resistant Enterobacterales (ENT) and non-fermenters (NFs). Bacteremia is a serious manifestation of GN infection and understanding how well an antibiotic works to clear the bacteremia is an important part of drug evaluation.
Methods. All completed clinical studies for CFDC development were used to identify patients with GN bacteremia. Information collected included the primary infection site, species identification and antibiotic susceptibility, post randomization blood cultures and clinical and bacteremia outcome. In patients with missing data (blood cultures) clinical response of cure was used to impute microbiological eradication. Indeterminate responses resulted from a combination of missing data and clinical failure, including death prior to test of cure (TOC).

Conclusion.
Post-treatment negative blood cultures were inconsistently collected, especially in APEKS-NP and -cUTI, however, negative blood cultures on therapy without recurrence was seen in 96% of CFDC patients with sufficient information. A dedicated clinical trial in GN bacteremia (GAME CHANGER; NCT03869437) is ongoing and will better delineate microbiological outcomes. Disclosures

Session: P-58. Novel Agents
Background. Rezafungin is a once-weekly novel echinocandin antifungal currently in Phase 3 development for treatment of candidemia and invasive candidiasis (ReSTORE) and for prevention of invasive fungal disease caused by Candida, Aspergillus, and Pneumocystis in blood and marrow transplant recipients (ReSPECT). Nonclinical ADME studies in rats and monkeys show rezafungin is primarily excreted unchanged in feces, with urine as a minor route. This study was conducted to characterize the routes of elimination of [ 14 C]-rezafungin and the pharmacokinetics of total radioactivity and plasma rezafungin in humans.
Methods. Nine healthy male subjects received a single IV 400-mg rezafungin infusion containing 200 µCi of [ 14 C]-rezafungin. Serial blood samples, urine, and feces were collected at specified times over 60 days; subjects were initially confined in the clinical research unit (CRU) for 17 days postdose and returned for two follow-up visits (days 29 and 60). During the period of time subjects were away from the CRU, recovery of radioactivity was estimated by linear interpolation.
Results. Rezafungin exhibited a long plasma half-life and was mainly excreted in feces unchanged. Cumulative recovery of radioactivity from excreta collected through the first 17 days was 52% (38% in feces, 14% in urine), reinforcing the slow overall elimination of rezafungin. Overall recovery of the administered dose by day 60 was estimated to be 88.3% (65.6% in feces, 22.7% in urine) (Figure 1). Mean blood/plasma concentration ratios ranged from 0.860 to 1.02 through the last collection time point (day 60), which indicated low association of radioactivity with blood cells. Rezafungin was the predominant compound measured in plasma and feces across all collected time points. In the urine, as observed in rat and monkey metabolite profiling studies, low level, inactive, oxidative metabolites were identified as 2-, 3-, 4-hydroxylpentyl rezafungin, and despentyl-rezafungin Figure 1 Conclusion: Results from this human excretion balance, metabolism and PK study are consistent with nonclinical results, which showed fecal excretion as the major route of elimination of rezafungin. Rezafungin was the predominant compound in plasma and feces.