Prior Medication Adherence Predicts Post-PCI Clopidogrel Compliance

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Patients’ record of adherence to daily medications before undergoing percutaneous coronary intervention (PCI) is a reliable guide to how well they will comply with dual antiplatelet therapy after the procedure, according to an analysis published online July 11, 2011, ahead of print in the American Journal of Cardiology.

Investigators led by Paul Muntner, PhD, of the University of Alabama at Birmingham (Birmingham, AL), studied 284 elective PCI patients enrolled in the ABCD-PCI (Ambulatory Closure Device Percutaneous Coronary Intervention) trial at Mount Sinai Hospital (New York, NY) and Baylor Heart and Vascular Hospital (Dallas, TX).

After PCI, patients filled out a predischarge questionnaire assessing multiple domains, including sociodemographics, cigarette smoking, health insurance status, barriers to filling medications, patient-physician communication, beliefs about medication, and adherence to daily medications. The last category was evaluated using the 8-item Morisky Medication Adherence Scale (MMAS-8), which explores reasons for nonadherence such as forgetfulness, health beliefs, and medication side effects.

Based on MMAS-8 scores, daily drug adherence was classified as:

  • Low (32% of patients)
  • Medium (35%)
  • High (32%)

Thirty days after PCI, trained research staff administered a follow-up questionnaire that specifically asked about clopidogrel use. Among patients who reported that they did not stop taking the drug, the MMAS-8 was again administered, this time tailored to apply to clopidogrel adherence.

Adherence Before Equals Compliance After

At 30 days after PCI, 11% of the overall cohort showed low compliance with clopidogrel therapy, 24% had medium compliance, and 65% demonstrated high compliance. The pattern at 1 month largely mirrored that of daily medication compliance before PCI, although patients tended to be somewhat more adherent to their antiplatelet regimen (table 1).

Table 1. Clopidogrel Compliance at 30 Days Stratified by Baseline Medication Use

Baseline Use

Low Clopidogrel Compliance

Medium Clopidogrel

High Clopidogrel

(n = 92)




(n = 100)




(n = 92)




Patients who showed low adherence to daily medications before PCI were more likely to have poor clopidogrel compliance at 30 days (OR 6.13; 95% CI 1.34-38.2), as were those who exhibited medium levels of prior adherence (OR 10.9; 95% CI 2.46-48.7).

In particular, 4 items from the predischarge MMAS-8 were associated with a greater likelihood of poor adherence to clopidogrel at 30 days:

  • Sometimes forgetting to take medications
  • Missed taking medications in the previous 2 weeks
  • Sometimes forgetting to bring medications when leaving home
  • Sometimes having difficulty remembering to take all medications

Overall, the predischarge MMAS-8 showed a strong ability to identify patients who would go on to have low clopidogrel adherence 30 days post PCI (c-statistic 0.733; 95% CI 0.650-0.815).

Other patient behaviors, largely due to socioeconomic status, were also found to predict poor compliance with dual antiplatelet therapy (table 2).

Table 2. Preprocedural Patient Characteristics Predictive of Low Clopidogrel Adherence



95% CI

P Value

Sometimes/often taking lower medication doses due to cost




Sometimes/often having difficulty filling prescriptions




Having difficulty reaching the doctor




Being uncomfortable asking the doctor to explain instructions





The investigators point out that the risks of early clopidogrel discontinuation, though not addressed by the current study, are well established: higher rates of stent thrombosis after DES implantation and all-cause mortality at 1 year.

Ferreting out factors that commonly contribute to failure to comply with dual antiplatelet therapy can guide development of a screening tool that is more accurate at predicting patients’ behavior than clinicians’ cursory assessment or gut instinct, the authors write. It can also inform development of interventions to increase adherence.

Meanwhile, the ability to identify beforehand patients who are likely to discontinue or have poor adherence to clopidogrel may affect clinical decision-making regarding PCI, for example driving the choice of BMS or balloon angioplasty over DES.

Dr. Muntner and colleagues acknowledge that their findings, which were based on low-risk patients, may not be generalizable to higher risk patients such as those with ACS. In addition, the researchers say that because of the small sample size, they pooled clopidogrel discontinuation and low adherence, which may have different causes and/or consequences.

Further research is needed to confirm the study findings and identify the best combination of pre-PCI questions to predict clopidogrel compliance, the authors conclude.

Findings Not Surprising—But Important

In a telephone interview with TCTMD, Renato D. Lopes, MD, PhD, MPH, of the Duke Clinical Research Institute (Durham, NC), said the paper adds new information about why some patients fail to comply with antiplatelet therapy, although he noted that the connection made with prior medication-taking habits is intuitive and not surprising.

“To me what is important is to bring the topic of noncompliance [to the fore] and identify contributing factors that are modifiable,” Dr. Lopes said. “That opens the door to a lot of interventions [to improve compliance], which then need to be tested prospectively to see if they change outcomes.”

Study coauthor Michael E. Farkouh, MD, MSc, of Mount Sinai Medical Center (New York, NY), told TCTMD the study is unique in using the highly regarded MMAS-8 scale, although he acknowledged that it adds cost and may not be practical to administer, especially in the urgent setting of ACS. “But it does help us understand what kinds of patients we’re dealing with so we can treat them better,” he said in a telephone interview.

As to whether assessment of a patient’s likelihood of complying with a post-stenting antiplatelet regimen should alter PCI strategy, that judgment varies from clinician to clinician, Dr. Lopes said, and depends in part on the lesion and coronary anatomy involved. “But in tertiary hospitals where you are more likely to get patients you don’t know, clinicians definitely take that into consideration in deciding on the type of stent to use,” he observed.

Dr. Farkouh added, “I’d be very hesitant to put a DES in a patient with a high likelihood of nonadherence.”

Communication Is Key

Providing patients with information and answering their questions are critical to improving compliance, Dr. Lopes commented. “Sometimes we think, ‘Okay, I’ve prescribed clopidogrel—I’m done.’ But if the patient does not understand the importance of taking the drug, my job is not done,” he said. In addition, before discharge, the compliance message should be reinforced by the entire medical team, Dr. Lopes suggested. 

According to Drs. Farkouh and Lopes, communication should also extend to patients’ primary care doctor and other treating physicians, who may recommend that patients discontinue clopidogrel before having a procedure such as a colonoscopy. “There needs to be a quarterback,” Dr. Farkouh emphasized, noting that “stopping therapy in these patients can lead to some fairly drastic consequences. Sometimes cardiologists have to go the extra distance to keep in touch with other doctors.” 

The bottom line is that “as cardiologists, we’re focused on the lesions, implanting the best devices, and the medical therapy at the time of intervention,” Dr. Farkouh said. “But we don’t spend a lot of time looking at what happens after the patients go home.”

Dr. Lopes echoed the same theme. “Studies like this are a kind of wake-up call, and the message is don’t forget the basics, like knowing and talking to your patients,” he said.

Study Details

The mean age of patients was 55.8 years and 26% were women. Caucasians accounted for 33% of the cohort, blacks for 15%, Hispanics for 26%, and Asians for 21%. 

Fewer patients with poor daily medication compliance received DES: 73.9% of those with low adherence, 81.0% with medium adherence, and 84.6% with high adherence.


Muntner P, Mann DM, Woodward M, et al. Predictors of low clopidogrel adherence following percutaneous coronary intervention. Am J Cardiology. 2011;Epub ahead of print.



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Prior Medication Adherence Predicts Post-PCI Clopidogrel Compliance

Patients’ record of adherence to daily medications before undergoing percutaneous coronary intervention (PCI) is a reliable guide to how well they will comply with dual antiplatelet therapy after the procedure, according to an analysis published online July 11, 2011, ahead
  • Dr. Muntner makes no statement regarding conflicts of interest.
  • Drs. Lopes and Farkouh report no relevant conflicts of interest.