Anti-Xa levels useful for therapy safety, drug concentration assessment

Monitoring of anti-Xa levels appears beneficial in evaluating current drug concentrations, ensuring immediate safety of therapy, and guiding possible clinical interventions, according to a study.

Adult inpatients on apixaban or rivaroxaban with at least one anti-Xa level ordered after administered doses were included in this retrospective, descriptive study.

Major bleeding according to the International Society on Thrombosis and Haemostasis criteria was the primary endpoint. Secondary ones were reasons for anti-Xa level ordering, anti-Xa levels at different time intervals postdose, and thrombotic events. The authors performed prespecified subgroup analyses to further assess the primary endpoint.

A total of 169 patients and 234 anti-Xa levels were assessed in this study. Twenty-nine levels were obtained in the context of major bleeding.

Most levels were not drawn as peak levels 2‒4 hours postdose but remained quantifiable above typical observed levels within this timeframe and even beyond 24 hours postdose. Characteristics of patients with major bleeding included old age, acute renal impairment, and low body weight.

Moreover, no less than 14 reasons for anti-Xa level ordering were identified. Of note, 29 levels were found to be associated with thrombotic events.

“Dose titration and reversal therapies based on anti-Xa level results in major bleeding warrant further research,” the authors said.

“Although not routinely recommended, anti-Xa level monitoring for apixaban or rivaroxaban may be useful in certain clinical scenarios. There are currently no laboratory standards, therapeutic ranges, or proven correlation between anti-Xa levels and clinical outcomes,” they noted.