# Anti-Factor Xa Activity of Apixaban in Extremely Low Body Weight

## TL;DR

This study shows that underweight patients taking apixaban have higher drug levels, which could increase the risk of side effects.

## Contribution

The study identifies low body weight as a key predictor of apixaban concentration exceeding therapeutic ranges.

## Key findings

- Underweight patients had significantly higher peak and trough apixaban concentrations than normal-weight patients.
- Low body weight was the only independent predictor of exceeding apixaban's peak concentration range.
- Most patients maintained apixaban levels within expected ranges, but underweight patients were more likely to exceed safe levels.

## Abstract

Background: Direct oral anticoagulants (DOACs) are generally preferred over warfarin for preventing arterial and venous thromboembolism. However, the efficacy and safety of DOACs in patients with extremely low body weight (BW) are uncertain. This study investigates anti-factor Xa (anti-FXa) activity of apixaban and compares it between patients with normal BW (>50 kg) and underweight (≤50 kg). Methods: We enrolled 150 patients on branded generic apixaban (ApixanTM) for atrial fibrillation (AF), venous thromboembolism, and intracardiac thrombus. Anti-FXa activity of apixaban was measured at peak concentration (Cpeak) and trough concentration (Ctrough) after at least one week of therapy. Results: Mean age was 64.0 ± 12.7 years, with 53.3% being male. Mean BW was 61.3 ± 15.3 kg. Of the 150 patients, 132 (88%) had AF, and 43 (28.7%) had low BW. Overall, 87.3% and 84.7% of patients had Ctrough and Cpeak within the expected range. Underweight patients had significantly higher mean Ctrough and Cpeak than normal BW patients. A higher proportion of low-BW patients exceeded the expected Cpeak range compared to normal-BW patients (25.6% vs. 3.7%, p < 0.001). Low BW was the only independent predictor of exceeding Cpeak specified range (adjusted OR 4.87, 95% CI 1.31–18.15, p = 0.018). Conclusions: Most patients maintained apixaban levels within expected ranges, but those with low BW were more likely to exceed the specified range of Cpeak.