Pharmacokinetics and Pharmacodynamics of Apixaban in Nephrotic Syndrome: Findings From a Phase 1a Trial

Nephrotic syndrome (NS) is associated with an elevated risk of venous thromboembolism (VTE), occurring in up to 25% of NS patients.1Cushman M. Epidemiology and risk factors for venous thrombosis.Semin Hematol. 2007; 44: 62-69Crossref PubMed Scopus (470) Google Scholar, 2Kerlin B.A. Ayoob R. Smoyer W.E. Epidemiology and pathophysiology of nephrotic syndrome-associated thromboembolic disease.Clin J Am Soc Nephrol. 2012; 7: 513-520Crossref PubMed Scopus (212) Google Scholar, 3Mahmoodi B.K. ten Kate M.K. Waanders F. et al.High absolute risks and predictors of venous and arterial thromboembolic events in patients with nephrotic syndrome: results from a large retrospective cohort study.Circulation. 2008; 117: 224-230Crossref PubMed Scopus (265) Google Scholar Guidelines advocate for primary thromboprophylaxis in select NS patients.4Kidney Disease: Improving Global Outcomes (KDIGO) Glomerular Diseases Work GroupKDIGO 2021 clinical practice guideline for the management of glomerular diseases.Kidney Int. 2021; 100: S1-S276PubMed Scopus (363) Google Scholar Warfarin, the most studied oral anticoagulant in NS, has been supplanted by direct oral anticoagulants in many other indications. Apixaban, a direct FXa inhibitor, has particular appeal owing to limited renal clearance and observational data suggesting it may be safe and effective with reduced glomerular filtration.5Hohnloser S.H. Hijazi Z. Thomas L. et al.Efficacy of apixaban when compared with warfarin in relation to renal function in patients with atrial fibrillation: insights from the ARISTOTLE trial.Eur Heart J. 2012; 33: 2821-2830Crossref PubMed Scopus (451) Google Scholar,6Eikelboom J.W. Connolly S.J. Gao P. et al.Stroke risk and efficacy of apixaban in atrial fibrillation patients with moderate chronic kidney disease.J Stroke Cerebrovasc Dis. 2012; 21: 429-435Abstract Full Text Full Text PDF PubMed Scopus (89) Google Scholar Because apixaban is highly protein bound (87%-93%, with 66% bound to albumin), the hypoalbuminemia and proteinuria common in NS could greatly influence apixaban pharmacokinetics and pharmacodynamics (PK/PD).7Wong P.C. Pinto D.J.P. Zhang D. Preclinical discovery of apixaban, a direct and orally bioavailable factor Xa inhibitor.J Thromb Thrombolysis. 2011; 31: 478-492Crossref PubMed Scopus (152) Google Scholar,8Byon W. Garonzik S. Boyd R.A. Frost C.E. Apixaban: a clinical pharmacokinetic and pharmacodynamic review.Clin Pharmacokinet. 2019; 58: 1265-1279Crossref PubMed Scopus (121) Google Scholar This single-institution, parallel-arm phase 1a study evaluated safety and PK/PD of a single apixaban dose in NS (NCT02599532). On day 1, participants were given oral apixaban while fasting, at 10 mg to mirror initial dosing guidance for VTE. Blood was collected prior to and 0.5, 1, 3, 4, 6, 8, and 24 hours after dose for PK analyses and anti-FXa levels. Blood samples were also collected at baseline and at 3, 6, and 24 hours to evaluate thrombin generation, and at baseline and 24 hours for quantitative D-dimer. Urinary protein-creatinine ratio (UPCR), baseline prothrombin time/international normalized ratio, activated partial thromboplastin time, and platelet count were evaluated prior to apixaban administration. Safety assessments were performed at baseline, prior to the 24-hour time point on day 2, and for the entire adverse event reporting period (0-48 hours) (Fig S1). We measured total and free fraction apixaban concentrations by liquid chromatography–tandem mass spectrometry. Functional apixaban concentrations were determined by a chromogenic anti-FXa assay. Detailed methods are included in Item S1. Eleven participants with NS (6 membranous nephropathy [MN], of which 3 were ineligible at the study visit (Fig S2); 4 focal segmental glomerulosclerosis; 1 minimal change) and 11 healthy controls were enrolled, and 19 completed the study. The groups had similar baseline characteristics (Table S1). Apixaban PK parameters are summarized in Table 1. We examined both total (ie, the protein-bound apixaban fraction plus the protein-unbound “free” apixaban fraction) and free (protein-unbound fraction only) apixaban. The Tmax of both total and free apixaban was 3 hours, indicating similar gastrointestinal absorption rates among all participants. There was no statistically significant difference in Cmax or AUC0-24 of total or free apixaban between NS and control participants. However, the Cmax value for free apixaban as a percentage of that of total circulating apixaban was lower in controls (6.5% [range: 3.6%-13.0%]) than in NS participants (9.1% [6.3%-13.7%]) and highest among those with severe NS (10.3% [6.3%-13.7%]). Similarly, for AUC0-24, corresponding values were 6.4% (5.0%-9.5%), 8.8% (7.0%-12.2%), 9.7% (7.6%-12.2%). While the observed ranges of free apixaban are consistent with published apixaban plasma protein binding estimates (87%-93%),7Wong P.C. Pinto D.J.P. Zhang D. Preclinical discovery of apixaban, a direct and orally bioavailable factor Xa inhibitor.J Thromb Thrombolysis. 2011; 31: 478-492Crossref PubMed Scopus (152) Google Scholar,8Byon W. Garonzik S. Boyd R.A. Frost C.E. Apixaban: a clinical pharmacokinetic and pharmacodynamic review.Clin Pharmacokinet. 2019; 58: 1265-1279Crossref PubMed Scopus (121) Google Scholar they suggest greater free fraction exposure in NS, possibly owing to decreased circulating albumin levels.Table 1Summary Statistics for Apixaban PK ParametersParameter EstimateHealthy Controls (n = 11)All NS Participants (n = 8)Severe NS Participants (n = 4)Total ApixabanFree ApixabanFunctional ApixabanTotal ApixabanFree ApixabanFunctional ApixabanTotal ApixabanFree ApixabanFunctional ApixabanCmax, ng/mL162.3 (38.2)10.6 (38.5)166.3 (34.9)146.8 (32.8)13.3 (33.1)155.3 (33.1)132.0 (21.9)13.6 (35.6)68.0 (67.4)Tmax, h3.0 [1.0-3.0]3.0 [1.0-4.0]2.2 [1.0-3.0]3.0 [1.0-4.0]3.0 [1.0-4.0]2.8 [1.0-4.0]3.03.03.0AUC0-24, ng•h/mL1,654.9 (31.6)106.2 (41.9)1,576.9 (26.4)1,539.4 (50.9)135.8 (46.5)1,651.0 (43.6)1,274.9 (45.4)124.1 (59.0)1,478.6 (54.1)Vd/F, L55.9 (39.4)1,162.8 (47.6)65.2 (32.1)65.3 (35.9)919.6 (44.6)74.6 (42.4)69.8 (25.1)1,037.9 (13.9)91.5 (23.6)t1/2, h7.3 ± 1.713.3 ± 4.212.6 ± 7.59.2 ± 4.612.6 ± 2.68.2 ± 1.57.4 ± 3.413.3 ± 1.814.6 ± 10.2CL/F, mL/h5,389.0 (29.8)62,929.3 (21.9)5,592.6 (22.1)5,386.4 (68.9)51,608.7 (43.1)4,614.9 (58.6)6,923.0 (40.9)54,512.7 (40.3)5,016.7 (46.9)Values given as geometric mean (% coefficient of variation), median [range if >1 value], or mean ± SD. Parameter estimates based on noncompartmental analyses. There were no significant differences for total or free apixaban concentrations or anti-FXa activity for NS vs control participants or for severe NS vs control participants. “All NS” includes those with severe NS (ie, UPCR >7 g/g and/or albumin <3.0 g/dL). Abbreviations: AUC0-24, overall exposure (area under the plasma concentration–time curve from time 0-24 hours); AUC0-∞, area under the plasma concentration–time curve from time 0 extrapolated to infinity; CL/F, apparent clearance; Cmax, maximum observed plasma concentration; FXa, factor Xa; t1/2, plasma terminal half-life; Tmax, time of observed maximum plasma concentration; Vd/F, apparent volume of distribution. Open table in a new tab Values given as geometric mean (% coefficient of variation), median [range if >1 value], or mean ± SD. Parameter estimates based on noncompartmental analyses. There were no significant differences for total or free apixaban concentrations or anti-FXa activity for NS vs control participants or for severe NS vs control participants. “All NS” includes those with severe NS (ie, UPCR >7 g/g and/or albumin <3.0 g/dL). Abbreviations: AUC0-24, overall exposure (area under the plasma concentration–time curve from time 0-24 hours); AUC0-∞, area under the plasma concentration–time curve from time 0 extrapolated to infinity; CL/F, apparent clearance; Cmax, maximum observed plasma concentration; FXa, factor Xa; t1/2, plasma terminal half-life; Tmax, time of observed maximum plasma concentration; Vd/F, apparent volume of distribution. Compared to controls, those with severe NS had 23% lower AUC0-24 and 28% higher CL/F of total apixaban (Table 1). In severe NS, the higher clearance of total apixaban was observed concurrently with 14% lower free apixaban clearance. Together these differences suggest more rapid clearance of total apixaban in severe NS is driven by a disproportionately greater clearance of the protein-bound apixaban fraction, possibly owing to increased proteinuria. Among NS participants, maximum free apixaban concentration and AUC0-24 were higher (25% and 28%, respectively), while CL/F was 18% slower than in controls. Collectively, these data could suggest that greater exposure to pharmacologically active free apixaban fraction could possibly translate to higher bleeding risk. At baseline, D-dimer and thrombin generation were nominally higher in NS than in control participants, but did not reach statistical significance. However, D-dimer at 24 hours post dose was significantly higher in NS participants. These and additional PK/PD results are included in Item S2 and Figs S3-S9. We found a single 10 mg dose of apixaban was safe, and non-steady-state PK/PD was similar between NS and control participants, with some variance dependent upon disease severity. Severity of hypoalbuminemia in NS is the most well-established risk factor for VTE,9Lionaki S. Derebail V.K. Hogan S.L. et al.Venous thromboembolism in patients with membranous nephropathy.Clin J Am Soc Nephrol. 2012; 7: 43-51Crossref PubMed Scopus (146) Google Scholar particularly for MN; NS participants with the highest VTE risk and greatest need for pharmacologic thromboprophylaxis may be most likely to have altered PK/PD for highly protein-bound drugs, such as apixaban.7Wong P.C. Pinto D.J.P. Zhang D. Preclinical discovery of apixaban, a direct and orally bioavailable factor Xa inhibitor.J Thromb Thrombolysis. 2011; 31: 478-492Crossref PubMed Scopus (152) Google Scholar,10Ganeval D. Fischer A.M. Barre J. et al.Pharmacokinetics of warfarin in the nephrotic syndrome and effect on vitamin K-dependent clotting factors.Clin Nephrol. 1986; 25: 75-80PubMed Google Scholar While we observed relatively similar PK/PD in NS and control participants (Fig 1; Figs S3-S8), notable differences could have potential clinical importance if validated, particularly among those with the most severe NS (eg, differences in total apixaban AUC0-24 and CL/F). However, the clinical implications of reduced exposure and increased clearance of total apixaban are currently unknown in a disease whose cardinal features could potentially affect the free fraction PK because all PK/PD measures in this study were assessed only after a single 10 mg dose. Clinically, we have observed apixaban anticoagulation failure in an MN patient who had recurrent VTE with lower than expected peak apixaban Xa activity, suggesting potentially reduced therapeutic efficacy.11Reynolds M.L. Nachman P.H. Mooberry M.J. Crona D.J. Derebail V.K. Recurrent venous thromboembolism in primary membranous nephropathy despite direct Xa inhibitor therapy.J Nephrol. 2019; 32: 669-672Crossref PubMed Scopus (13) Google Scholar Among those with severe NS, we noted increased exposure of free fraction apixaban with slower CL/F compared to controls, which was in contrast to the findings of total apixaban. These latter findings could suggest increased bleeding risk from free drug owing to prolonged exposure. However, the exact apixaban concentration leading to increased bleeding risk remains unknown, and the exposure differences we observed may not meet that threshold. Moreover, our toxicity data and present PD data do not confirm such an increased bleeding risk, but only capture changes from a single dose and not steady-state PD. While PK parameter differences for the pharmacologically free apixaban are descriptively different between NS and control participants, these data need both confirmation and assessment of their clinical relevance in a larger cohort of NS patients, and with steady-state apixaban PK measurements. Steady-state PD assessments may also reveal more differences between NS and control participants. Our observations remain hypothesis-generating given the single-dose study and small sample size. Future studies incorporating steady-state apixaban PK/PD will be needed to reveal the clinical significance of any alterations to free and total apixaban PK in NS, including those patients with more severe hypoalbuminemia or proteinuria. Our study used traditional PK/PD approaches (eg, quantification of total circulating apixaban and anti-FXa), in combination with innovative approaches to quantify circulating free apixaban and apixaban PD (eg, D-dimer and thrombin generation quantitation), to explore pharmacological differences for both bound and unbound apixaban vis-a-vis proteinuria and hypoalbuminemia in NS. We did note PK/PD differences, whose clinical consequences warrant further evaluation. Future multidose studies with steady-state measures of apixaban exposure, elimination, and PD (NCT04278729) can advise potential clinical studies of NS and VTE and inform clinically appropriate use of this agent for this population. Research idea and study design: VKD, TP, KAM, NSK, DJC; data acquisition: VKD, MLC, JRG, TP, AF, MRS, AHS, SMP, CDT, DMA, ST, RPG, NSK, DJC; data analyses and interpretations: VKD, JZ, MLC, JRG, SS, SMP, CDT, DMA, ST, RPG, NSK, DJC; statistical analyses: JZ, DJC; supervision or mentorship: VKD, DMA, ST, RPG, NSK, DJC. Each author contributed important intellectual content during manuscript drafting or revision and agrees to be personally accountable for the individual’s own contributions and to ensure that questions pertaining to the accuracy or integrity of any portion of the work, even one in which the author was not directly involved, are appropriately investigated and resolved, including with documentation in the literature if appropriate. Generous grant support provided by North Carolina Translational and Clinical Sciences (NC TraCS) and the National Center for Advancing Translational Sciences (550KR161709 to DJC, VKD, and NSK), and the American College of Clinical Pharmacy Research Institute (to DJC). Grant 5T32HL007148-43 supported JZ and SS (PI: NSK). Grant UL1TR002489 supported the NC TraCS Clinical and Translational Research Center, where the research was conducted. The funders of this study had no role in study design; collection, analysis, and interpretation of data; manuscript writing; and the decision-making process that determined where and when to submit the report for publication. VKD reports receipt of honoraria from UpToDate, and having served as a consultant for Novartis, Merck, Travere, Bayer, and Forma Therapeutics. The remaining authors declare that they have no relevant financial interests. The authors would like to thank the study participants, the staff of the UNC Nephrology Clinics for assistance with study recruitment, the staff of the UNC Clinical and Translational Research Center, and the staff of the NC TraCS Institute Clinical and Translational Research Center. Phoenix WinNonlin software was generously provided by Certara, Inc by designating the Division of Pharmacotherapy and Experimental Therapeutics at the UNC Eshelman School of Pharmacy as a Certara Center of Excellence. The authors would also like to thank Dr Ryan Beechinor, Dr Patrick Nachman, and Dr Paul Dombrower for their valuable input during the development phase of this trial. Last, the authors would like to thank Dr Lana Crona for providing medical writing and editing expertise. The content of this work is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. De-identified individual data that support the results will be shared beginning 9-36 months following publication, provided the investigator who proposes to use the data has approval from an IRB, Independent Ethics Committee, or Research Ethics Board, as applicable, and executes a data use/sharing agreement with UNC. Received March 29, 2021. Evaluated by 3 external peer reviewers, with direct editorial input from a Statistics/Methods Editor, an Associate Editor, and the Editor-in-Chief. Accepted in revised form September 6, 2022. Download .pdf (1.21 MB) Help with pdf files Supplementary File (PDF)Figures S1-S9; Items S1-S2; Tables S1-S2.