Can a Single Measurement of Apixaban Levels Identify Patients at Risk of Overexposure? A Prospective Cohort Study

Anticoagulants: From chance discovery to structure-based design

Taking a historical perspective, we review the discovery, pharmacology, and clinical evaluation of the old and new anticoagulants that have been approved for clinical use. The drugs are discussed chronologically, starting in the 1880s, and progressing through to 2024. The innovations in technology used to develop novel anticoagulants came in fits and starts and reflected the advances in science and technology over these decades, whereas the shift from anecdote to evidence-based use of anticoagulants was delayed until the principles of epidemiology and biostatistics were introduced into clinical trial design and to the approval process. Hirudin, heparin, and vitamin K antagonists were discovered by chance, and were used clinically before their mechanism of action was elucidated and before their net clinical benefits were evaluated in randomized clinical trials. Subsequent anticoagulants were designed based on a better understanding of the structure and function of coagulation proteins, including antithrombin, thrombin, and factor Xa, and underwent more rigorous preclinical and clinical evaluation before regulatory approval. By simplifying oral anticoagulation, the direct oral anticoagulants have revolutionized anticoagulation care and have enhanced the uptake of anticoagulation, but bleeding has not been eliminated and there is a need for more effective and convenient anticoagulants for thrombosis triggered by the contact pathway of coagulation. The newly developed factor XIa and XIIa inhibitors have the potential to address these unmet clinical needs and are undergoing clinical evaluation for several indications. SIGNIFICANCE STATEMENT: Anticoagulant therapy is the cornerstone of treatment and prevention of thrombosis, which remains a leading cause of morbidity and mortality worldwide. Elucidation of the structure and function of coagulation enzymes, their cofactors, and inhibitors, coupled with advances in structure-based design led to the discovery of more convenient, safer, and more effective anticoagulants that have revolutionized the management of thrombotic disorders.

Usual On-therapy Ranges of Drug Concentrations in Patients with Atrial Fibrillation Treated with Direct Oral Anticoagulants: A Systematic Review and Meta-analysis

BACKGROUND

 Although most patients with atrial fibrillation (AF) receiving a direct oral anticoagulant (DOAC) do not require drug concentration measurements, there are situations where such information could be useful. Existing guidance documents provide usual on-therapy ranges for drug concentrations, but these have important limitations.

METHODS

 This is a systematic review and meta-analysis of studies reporting trough and peak levels of DOAC regimens approved for stroke prevention in AF. We used random effects models and the quantile estimation method to estimate the median and a usual on-therapy range (10th and 90th percentiles).

RESULTS

 Of 4,822 unique publications, 53 studies met eligibility (29,266 trough and 12,103 peak levels). Usual on-therapy ranges for trough levels were 38 to 155 and 58 to 206 ng/mL for apixaban 2.5 and 5 mg twice daily; 35 to 138 and 33 to 151 ng/mL for dabigatran 110 and 150 mg twice daily; 8 to 54 and 13 to 66 ng/mL for edoxaban 30 and 60 mg daily; and 16 to 74 and 19 to 72 ng/mL for rivaroxaban 15 and 20 mg daily. The corresponding range for peak levels were 96 to 251 and 132 to 343; 65 to 223 and 76 to 285; 57 to 219 and 127 to 407; 131 to 384, and 169 to 313 ng/mL, respectively.

CONCLUSION

 This systematic review and meta-analysis provides updated and more representative usual on-therapy ranges of DOAC levels in patients with AF.

Plasma Drug Values of DOACs in Patients Presenting with Gastrointestinal Bleeding: A Prospective Observational Study

Background and Objectives: Anticoagulants are a well-known risk factor for gastrointestinal bleeding (GIB). In recent years, direct oral anticoagulants (DOACs) have taken a leading role in the treatment and prevention of thromboembolic incidents. The aim of this study was to investigate the prevalence of DOAC-treated patients with GIB whose plasma drug concentrations exceeded the cut-off values reported in the literature and to evaluate their clinical characteristics. Materials and Methods: Patients who were admitted to the Intensive Care Unit in the period 2/2020-3/2022 due to GIB were prospectively included in the study and classified into three groups according to the prescribed type of DOAC (apixaban, rivaroxaban, and dabigatran). For all participants, it was determined if the measured plasma drug levels exceeded the maximum serum concentration (Cmax) or trough serum concentration (Ctrough) obtained from the available data. A comparison of clinical parameters between the patients with and without excess drug values was performed. Results: There were 90 patients (54.4% men) included in the study, of whom 27 were treated with dabigatran, 24 with apixaban, and 39 with rivaroxaban. According to Cmax, there were 34 (37.8%), and according to Ctrough, there were 28 (31.1%) patients with excess plasma drug values. A statistically significant difference regarding excess plasma drug values was demonstrated between DOACs according to both Cmax (p = 0.048) and Ctrough (p < 0.001), with the highest rate in the group treated with dabigatran (55.6% for Cmax and 59.3% for Ctrough). Multivariate logistic regression showed that age (OR 1.177, p = 0.049) is a significant positive and glomerular filtration rate (OR 0.909, p = 0.016) is a negative predictive factor for excess plasma drug values. A total of six (6.7%) patients had fatal outcomes. Conclusions: Plasma drug concentrations exceed cut-off values reported in the literature in more than one-third of patients with GIB taking DOAC, with the highest rate in the dabigatran group. Clinicians should be more judicious when prescribing dabigatran to the elderly and patients with renal failure. In these patients, dose adjustment, plasma drug monitoring, or substitution with other, more appropriate DOACs should be considered.

Clinical Studies with Anticoagulants that Have Changed Clinical Practice

Anticoagulant therapy is the cornerstone of treatment and prevention of arterial and venous thromboembolism. Taking a historical perspective, starting in the 1960s, and progressing through to 2022, we discuss key clinical trials of anticoagulants that have changed clinical practice, and examine obstacles encountered in bringing these anticoagulants to the clinic. The design of some of the early studies that shaped clinical practice was poor by current standards, but their results were influential because nothing better was available. Both heparin and vitamin K antagonists had been in clinical use for several decades before well-designed trials in the 1980s optimized their dosing and enhanced their safety and efficacy. Low-molecular-weight heparin then replaced unfractionated heparin because it had a more predictable dose-response and a longer half-life, thereby allowing it to be used conveniently in out-of-hospital settings. More recently, direct oral anticoagulants became the oral anticoagulants of choice for most indications because they were shown to be at least as safe and effective as vitamin K antagonists when used in fixed doses without the need for laboratory monitoring. The design of the trials that led to the approval of the direct oral anticoagulants was excellent, but further studies are required to optimize their dosing in selected patients who were underrepresented in these trials.

Apixaban Concentrations in Routine Clinical Care of Older Adults With Nonvalvular Atrial Fibrillation

BACKGROUND

Direct-acting oral anticoagulants are first-line agents for prevention of stroke in patients with nonvalvular atrial fibrillation (NVAF), but data are limited for the oldest patients, and with reduced dosing.

OBJECTIVES

To determine steady-state apixaban peak and trough concentrations during routine care of older adults with NVAF, compare concentrations to clinical trial concentrations, and explore factors associated with concentrations.

METHODS

A cross-sectional study of medically stable older adults with NVAF (≥75 years or ≥70 years if Black) receiving apixaban. Peak (2-4.4 hours post-dose) and trough (before next dose) concentrations were determined by anti-Xa activity calibrated chromogenic assay. Patient characteristics associated with concentrations were determined by multivariate modeling.

RESULTS

The median age of patients (n = 115) was 80 (interquartile range: 77-84) years. The cohort comprised 46 women and 69 men; of which 98 are White, 11 Black, and 6 Asian. With 5 mg twice daily per labelling (n = 88), peak concentrations were higher in women: 248 ± 105 vs 174 ± 67 ng/mL in men (P < 0.001) and exceeded expected 95% range in 6 of 30 vs 0 of 55 men (P = 0.002). With 2.5 mg twice daily per label (n = 11), concentrations were <5 mg twice daily (peak: 136 ± 87 vs 201 ± 90 ng/mL, P = 0.026; trough: 65 ± 28 vs 109 ± 56 ng/mL, P < 0.001), but not different than 2.5 mg twice daily without reduction criteria (n = 13; peak: 132 ± 88; trough: 65 ± 31 ng/mL). Covariates associated with concentrations included sex, number of daily medications, and creatinine clearance.

CONCLUSIONS

Older women had higher than expected peak apixaban concentrations, and 2.5 mg twice daily produced lower concentrations than standard dosing. Factors not currently included in dosing recommendations affected concentrations. The impact of apixaban concentrations on outcomes needs evaluation.