The Renal Elimination Pathways of the Dabigatran Reversal Agent Idarucizumab and its Impact on Dabigatran Elimination

Is there a role for the laboratory monitoring in the management of specific antidotes of direct oral anticoagulants?

Given the growing number of patients receiving direct oral anticoagulant (DOAC), patients requiring rapid neutralization is also increasing in case of major bleedings or urgent surgery/procedures. Idarucizumab is commercialized as a specific antidote to dabigatran while andexanet alfa has gained the Food and Drug Administration and the European Medicines Agency approval as an oral anti-factor Xa inhibitors antidote. Other antidotes or hemostatic agents are still under preclinical or clinical development, the most advanced being ciraparantag. DOAC plasma levels measurement allows to appropriately select patient for antidote administration and may prevent unnecessary prescription of expensive molecules in some acute clinical settings. However, these tests might be inconclusive after some antidote administration, namely andexanet alfa and ciraparantag. The benefit of laboratory monitoring following DOAC reversal remains unclear. Here, we sought to provide an overview of the key studies evaluating the safety and efficacy of DOAC reversal using the most developed/commercialized specific antidotes, to discuss the potential role of the laboratory monitoring in the management of patients receiving DOAC specific antidotes and to highlight the areas that deserve further investigations in order to establish the exact role of laboratory monitoring in the appropriate management of DOAC specific antidotes.

Payload-Binding Fab Fragments Increase the Therapeutic Index of MMAE Antibody-Drug Conjugates

Monomethyl auristatin E (MMAE) is a potent tubulin inhibitor that is used as the payload for four FDA-approved antibody-drug conjugates (ADC). Deconjugated MMAE readily diffuses into untargeted cells, resulting in off-target toxicity. Here, we report the development and evaluation of a humanized Fab fragment (ABC3315) that enhances the therapeutic selectivity of MMAE ADCs. ABC3315 increased the IC50 of MMAE against human cancer cell lines by > 500-fold with no impact on the cytotoxicity of MMAE ADCs, including polatuzumab vedotin (PV) and trastuzumab-vc-MMAE (TvcMMAE). Coadministration of ABC3315 did not reduce the efficacy of PV or TvcMMAE in xenograft tumor models. Coadministration of ABC3315 with 80 mg/kg TvcMMAE significantly (P < 0.0001) increased the cumulative amount of MMAE that was excreted in urine 0 to 4 days after administration from 789.4±19.0 nanograms (TvcMMAE alone) to 2625±206.8 nanograms (for mice receiving TvcMMAE with coadministration of ABC3315). Mice receiving 80 mg/kg TvcMMAE and PBS exhibited a significant drop in white blood cell counts (P = 0.025) and red blood cell counts (P = 0.0083) in comparison with control mice. No significant differences, relative to control mice, were found for white blood cell counts (P = 0.15) or for red blood cell counts (P = 0.23) for mice treated with 80 mg/kg TvcMMAE and ABC3315. Coadministration of ABC3315 with 120 mg/kg PV significantly (P = 0.045) decreased the percentage body weight loss at nadir for treated mice from 11.9%±7.0% to 4.1%±2.1%. Our results demonstrate that ABC3315, an anti-MMAE Fab fragment, decreases off-target toxicity while not decreasing antitumor efficacy, increasing the therapeutic window of MMAE ADCs.

Clinical Pharmacokinetics of Approved RNA Therapeutics

RNA-mediated drugs are a rapidly growing class of therapeutics. Over the last five years, the list of FDA-approved RNA therapeutics has expanded owing to their unique targets and prolonged pharmacological effects. Their absorption, distribution, metabolism, and excretion (ADME) have important clinical im-plications, but their pharmacokinetic properties have not been fully understood. Most RNA therapeutics have structural modifications to prevent rapid elimination from the plasma and are administered intravenously or subcutaneously, with some exceptions, for effective distribution to target organs. Distribution of drugs into tissues depends on the addition of a moiety that can be transported to the target and RNA therapeutics show a low volume of distribution because of their molecular size and negatively-charged backbone. Nucleases metabolize RNA therapeutics to a shortened chain, but their metabolic ratio is relatively low. Therefore, most RNA therapeutics are excreted in their intact form. This review covers not only ADME features but also clinical pharmacology data of the RNA therapeutics such as drug-drug interaction or population pharmacokinetic analyses. As the market of RNA therapeutics is expected to rapidly expand, comprehensive knowledge will contribute to interpreting and evaluating the pharmacological properties.

The Nonclinical Disposition and PK/PD Properties of GalNAc-conjugated siRNA Are Highly Predictable and Build Confidence in Translation to Man

Conjugation of oligonucleotide therapeutics, including small interfering ribonucleic acids (siRNAs) or antisense oligonucleotides (ASOs) to N-acetylgalactosamine (GalNAc) ligands has become the primary strategy for hepatocyte-targeted delivery, and with the recent approvals of GIVLAARI® (givosiran) for the treatment of acute hepatic porphyria, OXLUMO^TM (lumasiran) for the treatment of primary hyperoxaluria, and Leqvio® (inclisiran) for the treatment of hypercholesterolemia, the technology has been well-validated clinically. While much knowledge has been gained over decades of development there is a paucity of published literature on the DMPK properties of GalNAc-siRNA. With this in mind the goals of this mini-review are to provide an aggregate analysis of these nonclinical ADME data to build confidence on the translation of these properties to human. Upon subcutaneous administration, GalNAc-conjugated siRNAs are quickly distributed to the liver, resulting in plasma pharmacokinetic (PK) properties that reflect rapid elimination through ASGPR-mediated uptake from circulation into hepatocytes. These studies confirm that liver PK, including half-life and, most importantly, siRNA levels in RNA-induced silencing complex (RISC) in hepatocytes are better predictors of pharmacodynamics (PD) than plasma PK. Several in vitro and in vivo nonclinical studies were conducted to characterize the absorption, distribution, metabolism and excretion (ADME) properties of GalNAc-conjugated siRNAs. These studies demonstrate that the PK/PD and ADME properties of GalNAc-conjugated siRNAs are highly conserved across species, largely predictable, and can be accurately scaled to human, allowing us to identify efficacious and safe clinical dosing regimens in the absence of human liver PK profiles. Significance Statement Several nonclinical ADME studies have been conducted in order to provide a comprehensive overview of the disposition and elimination of GalNAc-conjugated siRNAs and the PK/PD translation between species. These studies demonstrate that the ADME properties of GalNAc-conjugated siRNAs are well correlated and predictable across species building confidence in the ability to extrapolate to human.

Refractory Dabigatran-Induced Hemorrhage Despite Multiple Idarucizumab Administration and Renal Replacement Therapy

PURPOSE

This case report describes a patient with dabigatran accumulation due to acute kidney injury on chronic kidney disease, requiring multiple administration of idarucizumab along with renal replacement therapy because of rebound effect causing numerous episodes of bleeding.

SUMMARY

An 86-year-old man on dabigatran etexilate 110 mg twice daily for stroke prevention with atrial fibrillation was admitted to the hospital for bowel obstruction and severe acute kidney injury on chronic kidney disease. The patient had an abnormal coagulation profile and no history of bleeding. Initial laboratory values revealed a hemoglobin concentration of 10.7 g/dL, a platelet count of 115 × 10³ platelets/μL, an activated partial thromboplastin time of 150.4 seconds, an international normalized ratio of 10.28, a thrombin time greater than 100 seconds and a serum creatinine of 5.54 mg/dL (490 μmol/L). An initial dose of idarucizumab was administered 1 hour prior to surgery to prevent bleeding. Significant bleeding and hemodynamic instability occurred following surgery. Three additional doses of idarucizumab, 2 sessions of intermittent hemodialysis, continuous venovenous hemofiltration and blood products were required to achieve normalization of coagulation parameters and hemodynamic stability due to rebound coagulopathy after each dose of idarucizumab.

CONCLUSION

Acute kidney injury on chronic kidney disease and third-space redistribution could have led to important dabigatran accumulation and favored rebound coagulopathy. Multiple therapeutic approaches may be required in the management of complex dabigatran intoxication.

Dabigatran Reversal With Idarucizumab in Patients With Renal Impairment

BACKGROUND

Dabigatran and idarucizumab, its reversal agent, are renally cleared.

OBJECTIVES

The purpose of this study was to determine the extent of reversal and outcomes according to baseline renal function in dabigatran-treated nondialysis patients receiving idarucizumab.

METHODS

In 503 patients in RE-VERSE AD (Reversal of Effects of Idarucizumab in Patients on Active Dabigatran), the extent of dabigatran reversal and clinical outcomes were compared according to baseline renal function (creatinine clearance: normal ≥80, mild 50 to <80, moderate 30 to <50, and severe <30 ml/min).

RESULTS

Compared with patients with normal renal function, those with impaired renal function were older, were more often women, and had lower body mass indexes, more comorbidities, higher CHADS₂ scores, and higher dabigatran plasma levels despite more frequent use of lower-dose dabigatran regimens. Regardless of renal function, median reversal measured by dilute thrombin time was 100% within 4 h of idarucizumab administration, and over 98% of patients achieved this with corresponding undetectable levels of unbound dabigatran. By 12 or 24 h, 56% of patients with severe, 29.1% with moderate, and 9.2% with mild renal impairment had dabigatran levels >20 ng/ml compared with 8.3% of patients with normal renal function at baseline. Time to cessation of bleeding and the proportion with normal hemostasis with procedures were similar regardless of renal function, but patients with severe renal impairment had higher 30- and 90-day mortality rates.

CONCLUSIONS

Idarucizumab completely reverses dabigatran in >98% of patients regardless of renal function. Although re-elevation of dabigatran levels within 12 to 24 h is more common with renal impairment, the time to bleeding cessation and the extent of hemostasis during procedures are similar. (Reversal of Dabigatran Anticoagulant Effect With Idarucizumab; NCT02104947).

The (Fab)ulous Destiny of Idarucizumab: Highlighting Its Interference with Urine Protein Immunofixation

Idarucizumab is a humanized antigen binding fragment (Fab) of a recombinant anti-dabigatran monoclonal antibody (IgG1-kappa) that allows rapid and sustained reversal of dabigatran-induced anticoagulation in case of bleeding or urgent surgery. Herein, we report a very unusual case of dabigatran reversal by idarucizumab in a 79-year-old woman with acute kidney failure admitted to a hospital in a context of hemoptysis. Three repeated injections were necessary because of massive dabigatran overdose and high rebounds of dabigatran plasma concentration. Idarucizumab was found on urine immunofixation up to 6 days after the last injection where it reacted with anti-kappa light chain antibody, but not with anti-gamma heavy chain antibody. Physicians should be aware of the increased half-life of idarucizumab in this context of acute kidney impairment and of its interference with urine immunofixation because it could lead to false-positive results and misdiagnosis of a paraprotein.