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ORLANDO -- Patients who took direct oral anticoagulants (DOACs) along with aspirin for which there was no obvious indication were at significantly greater risk of suffering non-major bleeding in a retrospective study reported here, with a trend toward higher rates of life-threatening bleeding.

Among patients in a Michigan state registry, those without diagnoses for which the combination of aspirin plus DOAC is indicated experienced clinically relevant non-major bleeding at a rate of 18.70 per 100 patient-years, compared with 13.50 for propensity-matched patients receiving DOACs alone (P=0.02), said Jordan Schaefer, MD, of the University of Michigan.

Similarly, rates of all non-major bleeding were 32.82 per 100 patient-years for patients taking the combination versus 25.88 per 100 patient-years with DOACs alone (P=0.04), he reported at the .

Rates of more severe bleeding did not differ significantly between groups, perhaps because there were too few in the 1,278-patient sample. But life-threatening bleeding occurred at rates of 1.73 per 100 patient-years with an aspirin-DOAC combination, compared with 1.23 per 100 patient-years with DOACS alone. Overall new bleeds also trended higher with the combination (39.50 vs 32.32 per 100 patient-years, P=0.07).

Mark Crowther, MD, of McMaster University in Hamilton, Ontario, who moderated a press briefing where Schaefer discussed these results, commented that the field of venous thromboembolism (VTE) prevention has reached a turning point.

With "many new innovations over the last decade in the treatment of [VTE], we're now starting to refine how we manage patients with VTE or at risk for VTE," he said. "The results [of Schaefer's study] suggest a need for careful consideration of the relative risks and benefits of adding or continuing aspirin for patients on DOAC therapies."

Schaefer explained that the combination is sometimes indicated in patients with certain conditions, such as . Such patients, as well as those receiving heart valve replacement ( recommend against their use for such patients, Crowther noted) were excluded from the analysis. For other patients, there are no guideline recommendations or other commonly accepted reasons to combine aspirin and DOACs.

Many of these patients may have started DOACs while already taking aspirin, and Crowther suggested that many patients simply self-prescribe it. Because it's so familiar and widely available, he said, "patients don't think of aspirin as being a drug. They take it because they think it's something to make them healthy.... They don't realize it has consequences."

The analysis began with 2,045 patients with non-valvular atrial fibrillation or VTE in the Michigan Anticoagulation Quality Improvement Initiative receiving DOACs, of whom 645 were also taking aspirin. Schaefer and colleagues selected 639 of the latter along with 639 other registry patients matched according to standard risk factors for bleeding as well as comorbidities, DOAC type and dose, demographics, and indication for anticoagulation. Follow-up after treatment began averaged about 15 months.

Besides bleeding events, the researchers also looked at emergency department visits and hospital admissions in the two groups. These also trended higher with aspirin-DOAC combinations (17.96 vs 14.61 per 100 patient-years for emergency visits, 11.76 vs 9.04 per 100 patient-years for admissions; both P=0.14).

Schaefer said the findings warrant "larger confirmatory studies," with particular attention to patient subgroups.

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