Background: Patients of low body weight (LBW) were under-represented in phase-III clinical trials for DOACs and experience using these agents in this population is lacking. Guidance recommends LBW patients have therapeutic drug monitoring (TDM) with anti-Xa levels.
Aims: Review anti-Xa levels and clinical management of LBW ( < 55kg) patients prescribed DOACs at GSTT between 01/01/2018 and 31/12/2019.
Methods: Anti-Xa levels conducted between 01/01/2018-31/12/2019 were extracted from laboratory records and records reviewed to identify patients weighing < 55kg, date and time of previous dose, DOAC regime, past medical history, renal function, dose changes as a result of level, bleeding or thrombotic event within 3-months of level and current anticoagulation regime of patient was recorded. Descriptive statistics were used and non-parametric tests were used to compare categorical variables.
Results: 83 anti-Xa levels from 45 unique LBW patients were available for analysis. Median weight was 51.2kg (IQR: 44.5-53.1), Table 1. Of the anti-Xa levels available, 27 were peak levels (32.5%) and 20 were troughs levels (24.1%). The remaining 36 (43.4%) were neither peak or trough with 15 (18.1%) having no documented time of last dose or sample. Levels were within reference range for 33 (70.2%) samples (Table 2). Dose changes were made following high anti-Xa levels in 5 (50%) cases. Patients prescribed the licensed dose in this cohort were more likely to have a peak or trough result outside of the reference range (Chi sq=4.889, p=0.027). In the 3-months following each assay, 5 (11%) patients experienced a bleeding event, 1 (20%) of which was major (Table 2). 1 (2.2%) patient experienced a line associated thrombus.
Conclusion(s): DOACs are potentially suitable for use in LBW. Whilst dosing decisions should not be based on anti-Xa levels in the general population, it may be beneficial in LBW. Anti-Xa levels above the reference range was not associated with bleeding.
To cite this abstract in AMA style:Bartoli- Abdou J, Collings V, Acar S, Bahra G, McCutcheon N, Mahir Z, Breen K. Experience of Therapeutic Drug Monitoring in Patients Prescribed Direct Oral Anticoagulants (DOACs) of Low Body Weight ( < 55kg) at Guy’s & St Thomas’ NHS Foundation Trust [abstract]. https://abstracts.isth.org/abstract/experience-of-therapeutic-drug-monitoring-in-patients-prescribed-direct-oral-anticoagulants-doacs-of-low-body-weight-55kg-at-guys-st-thomas-nhs-foundation-trust/. Accessed September 29, 2023.
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