Nearly one-third of patients who underwent percutaneous coronary intervention (PCI) to treat myocardial infarction (MI) did not fully adhere to their prescribed medications six weeks after their MI, according to an analysis of a study at 216 U.S. hospitals.

Lead researcher Robin Mathews, MD, MPH, of the Duke Clinical Research Institute in Durham, North Carolina, and colleagues said patients had a higher likelihood of nonadherence if they were depressed or had trouble paying for medications. Patients were more likely to be adherent if they scheduled a follow-up appointment before leaving the hospitals and if a provider explained the medications’ side effects.

The findings were published online in Circulation: Cardiovascular Quality Outcomes on June 2.

Previous studies found that more than 25 percent of patients with MI did not fill their prescriptions within a week after leaving the hospital. Mathews et al noted the medication nonadherence was associated with worse outcomes and higher costs.

In this study, they analyzed the TRANSLATE-ACS (Treatment with ADP Receptor Inhibitors: Longitudinal Assessment of Treatment Patterns and Events after Acute Coronary Syndrome) trial that examined 7,425 patients with MCI who were treated with PCI between April 2010 and May 2012.

To measure adherence at six weeks, they used the eight-question Morisky Medication Adherence Scale (MMAS) and asked patients via telephone about their adherence to cardiovascular medications.

They defined the high adherence group as patients who scored an eight on the scale, meaning they answered no to all of the questions. The moderate group scored a six or seven, while the low group scored below six.

Of the patients, 71 percent were in the high adherence group, 25 percent were in the moderate adherence group and 4 percent were in the low adherence group.

In addition, 95.7 percent of patients said they received written instructions regarding their medications when they were discharged from the hospital, although patients in the low adherence group were less likely to have a provider explain why they were prescribed the medications.

The researchers also mentioned patients in the low adherence group were less likely to monitor their blood pressure or exercise on a regular basis compared with the other groups.

They noted a few limitations, including that adherence was patient-reported and not verified and that they only assessed adherence at one time point. However, they said the MMAS was a validated questionnaire.