No significant difference in cardiovascular events or major bleeding was shown between patients with established coronary heart disease assigned to a daily aspirin dose of 81 mg and those receiving a dose of 325 mg in the 15,000-patient ADAPTABLE trial.
Although substantial dose switching occurred in the trial, particularly from the higher to the lower dose, lead investigator W. Schuyler Jones, MD, believes the results support the use of the 81-mg dose in most patients.
“While we would have liked to see higher adherence to the assigned doses, we think the results of the trial are reliable,” Dr. Jones said in an interview.
The real-world, open-label, pragmatic trial also involved an innovative low-cost design allowing researchers to identify and communicate with eligible patients directly, opening up a new cost-effective method to conduct clinical research going forward.
Dr. Jones, a cardiologist and associate professor of medicine at Duke University Medical Center, Durham, N.C., presented the ADAPTABLE results at the annual scientific sessions of the American College of Cardiology. They were simultaneously published online in the New England Journal of Medicine.
He noted there were mixed signals in the results. “For example, the main intent-to-treat analysis showed a trend to a lower rate of all-cause death in the 81-mg group, but the subgroup of patients who stayed on the 325-mg dose throughout the study had a lower event rate. But overall, there was no difference.”
Dr. Jones said the investigators had the following take-home messages to patients: “If a patient is already taking 81 mg, staying on this dose is probably right given the similar study results for the primary endpoint and that we didn’t find conclusive evidence that 325 mg is better. But for patients who have tolerated 325 mg long term, then they may want to stay on this dose as it may be associated with moderate benefit.”
Dr. Jones pointed out that, overall, patients who switched doses tended to do worse, but he suggested this may have been more to do with underlying reasons for switching rather than the different dose itself. “For example, switching often happens after bleeding or bruising, which can also often preempt an ischemic event, and other illnesses, such as cancer or atrial fibrillation, can also lead patients to change doses.”
“With the caveat that this trial did not include new patients (the vast majority of patients had been taking aspirin previously) the results support the approach of starting new patients on 81 mg, which is what we have been seeing in evolving clinical practice in recent years,” he added.
Dr. Jones explained that the trial set out to answer the simple but important question about the best dose of aspirin in patients with heart disease.
“Aspirin has been established as an appropriate long-term medication for patients with ischemic heart disease since the 1980s, but we really don’t have any good information on the correct dose.
He noted that the U.S. guidelines suggest any dose in the range of 81 mg to 325 mg daily can be used, whereas the European guidelines recommend 81 mg daily, although this is mainly based on observational data and expert opinion; there is little hard, randomized-trial evidence.
The ADAPTABLE trial randomly assigned 15,076 patients with established heart disease to receive 81 mg or 325 mg of aspirin. Before randomization, 96% of those with available information were already taking aspirin, 85% of whom were taking 81 mg.
After a mean follow-up of 26 months, the primary efficacy endpoint – a composite of all-cause death, myocardial infarction, or stroke – had occurred in 7.28% of the 81-mg group and 7.51% of the 325-mg group (hazard ratio, 1.02; 95% confidence interval, 0.91-1.14).
The main safety endpoint, hospitalization for major bleeding with an associated blood transfusion, occurred in 0.63% of the 81-mg group and 0.60% of the 325-mg group (HR, 1.18; 95% CI, 0.79-1.77).
“The bleeding safety endpoint looked similar, which may be counterintuitive to what may have been expected,” Dr. Jones commented. “However, the safety endpoint was very stringent. We still haven’t analyzed all the less serious ADR [adverse drug event]/bleeding data, but overall, it does appear to be balanced.”
He added: “Most cardiologists probably may not have expected to see much difference in efficacy between these two doses but would maybe have anticipated a lower bleeding rate with the low dose. I was a little surprised to see such a low bleeding rate in the 325-mg group.”
Patients assigned to 325 mg had a higher incidence of dose switching (41.6%) than those assigned to 81 mg (7.1%) and were more likely to discontinue treatment (11.1% vs. 7.0%). This resulted in fewer median days of exposure to the assigned dose in the 325-mg group (434 vs. 650 days).
“This was an open-label study, and such studies always suffer from a degree of infidelity to the assigned treatment group,” Dr. Jones said. “In ADAPTABLE, this was unbalanced in that a much greater number of patients switched from 325 mg to 81 mg than the other way round.”
“But our results do reflect what happens in normal life,” he added. “People behaved in the study like they do in the real world. They sometimes changed their dose and sometimes stopped taking aspirin altogether. So, I think the results are an accurate representation of the real world.”
A sensitivity analysis based on which dose the patient actually reported taking showed a higher risk for death, MI, or stroke in patients who took 81 mg than those who took 325 mg (HR, 1.25; 95% CI, 1.10-1.43). But as with any postrandomization analysis, this approach has many inherent biases, Dr. Jones cautioned.