Comparative Analysis of Anticoagulation Stability in Critically Ill Patients Receiving Argatroban for Suspected or Confirmed Heparin-Induced Thrombocytopenia Compared with Unfractionated Heparin: A Retrospective Cohort Study

Background: Achieving and maintaining therapeutic anticoagulation with unfractionated heparin in critically ill patients is challenging due to biologic variability, heparin resistance, and limitations of activated partial thromboplastin time (aPTT) monitoring. Argatroban, a direct thrombin inhibitor, provides antithrombin-independent anticoagulation with more predictable pharmacokinetics, but real-world data describing its anticoagulation stability in the intensive care unit (ICU) remain limited. Objective: This study aimed to compare anticoagulation stability between continuous intravenous argatroban and unfractionated heparin in critically ill patients using time in therapeutic range (TTR) based on aPTT as the primary performance metric. Methods: A retrospective cohort study was conducted in the ICU and step-down unit of Hôpital Montfort (Ottawa, ON, Canada) between January 2016 and December 2024. Adult patients receiving continuous intravenous argatroban or unfractionated heparin for systemic anticoagulation were included. All aPTT values obtained during active infusion were extracted, and TTR was calculated using linear interpolation between consecutive measurements. Continuous variables were summarized as medians with interquartile ranges and compared using the Wilcoxon rank-sum test; categorical TTR strata were compared using Fisher’s exact test. Results: Sixty-eight patients met the inclusion criteria, contributing 9 argatroban and 61 heparin infusion courses. Argatroban demonstrated a higher median TTR than heparin (83.3% [IQR 82.0–90.7] vs. 47.5% [32.9–62.4]; p < 0.001), with a moderate-to-large effect size (r = 0.51). Median aPTT values were similar between groups, but argatroban showed narrower dispersion and fewer prolonged subtherapeutic periods. A majority of heparin courses (56.5%) spent <50% of time within range, whereas no argatroban courses fell into this category. Conversely, 33.3% of argatroban courses achieved ≥90% TTR compared with none in the heparin group. Conclusions: In this real-world ICU cohort where argatroban was used for suspected or confirmed HIT, argatroban was associated with higher TTR than unfractionated heparin. These findings support the use of time-dependent metrics to evaluate anticoagulation quality and warrant prospective studies in more homogeneous populations.