When patients don't pick up — or "abandon" — a prescription, a high co-payment is often the reason, a new study by Harvard, Brigham and Women's Hospital and CVS Caremark Corp. finds.

Researchers found a direct link between the amount of a patient's out-of-pocket co-pay and the likely abandonment of the prescription. "Sticker shock is an important driver of prescription abandonment," the study's lead author commented.

WOONSOCKET, R.I. — When patients don’t pick up — or "abandon" — a prescription, a high co-payment is often the reason, a new study by Harvard, Brigham and Women’s Hospital and CVS Caremark Corp. finds.

CVS Caremark said Tuesday that researchers found a direct correlation between the amount of a patient’s out-of-pocket co-pay and likely abandonment of the prescription. Patients with a co-pay of $50 almost four times more likely to abandon a prescription at a pharmacy than those paying $10.

In addition, the study found that electronic prescriptions are 65% more likely to be left abandoned at a retail pharmacy by patients than are hand-written prescriptions.

The CVS Caremark-sponsored study, published this week in the Annals of Internal Medicine, is the first to systematically evaluate rates and predictors of prescriptions abandoned at the pharmacy, the company said.

"Sticker shock is an important driver of prescription abandonment," commented the study’s lead author, William Shrank, M.D., of Brigham and Women’s Hospital and Harvard. The research also outlines and validates a simple prediction rule that pharmacists can apply to help them assess whether patients are at risk to abandon their prescriptions, Shrank added.

The research team reviewed all prescriptions dispensed at CVS/pharmacy locations between July 1 and Sept. 30, 2008. Of the prescriptions abandoned, more than half were never filled at any pharmacy, and some were filled at other pharmacies at a later date.

Study data show a 1.4% prescription abandonment rate for patients with co-pays of $10 or less, a 3.4% rate for patients with co-pays between $30 and $40, and a 4.7% rate for patients with co-pays of $50.

If the 3.27% abandonment rate observed during the study period is applied to the 3.6 billion prescriptions filled at pharmacies in 2008, researchers said, approximately 110 million prescriptions would be abandoned.

Researchers concluded that the pharmacy industry would benefit from learning more about prescription abandonment, which impacts patient medication adherence.

"This research gives us new insight into an area of nonadherence that we did not have before and shows we have opportunities to change patient behavior," Larry Merlo, president and chief operating officer of CVS Caremark, said in a statement.

"We need to be more attentive to reasons why patients may be abandoning prescriptions and work to help them stay on their medications," Merlo explained. "We continue to be a strong proponent of e-prescribing because we recognize the benefits it can provide, such as improving the accuracy and quality of prescription delivery and reducing paperwork to make pharmacy care more efficient."

The higher rate of abandonment for e-prescriptions appears to occur because patients with written prescriptions must physically bring the request for medications to the pharmacy, whereas patients with e-prescriptions don’t have to take any step to begin the prescription filling process, the researchers said. E-prescription abandonment also appears high because pharmacies can track them as abandoned versus paper prescriptions that are never actually brought to a pharmacy.

Researchers outlined a predictive model for pharmacists to apply to help them recognize likely candidates for abandonment:

• Review the patient’s benefit plan and tiered co-pays. The study found that cost is the strongest predictor of abandonment.

• Understand past pharmacy behavior. Patients with first-fill prescriptions are three times more likely to abandon prescriptions than those who are refilling their medication.

• Identify the age of the patient. Younger patients are more likely than older patients to abandon their medications.

• Review the drug class. The study found that opiates, anti-platelets and statins were the least likely to be abandoned, while insulin and proton pump inhibitors were more likely to be abandoned.

CVS Caremark said the prescription abandonment study is part of its research effort aimed at better understanding how consumers interact with their pharmacy so they stay adherent to their medications. The study is the work of CVS Caremark’s previously announced three-year collaboration with Harvard University and Brigham and Women’s Hospital to research pharmacy claims data to better understand patient behavior around medication adherence.

The company added that past industry studies show that a quarter of people receiving prescriptions never fill their first prescriptions, and patients with chronic diseases such as diabetes and coronary artery disease adhere to their ongoing medication regimen about half of the time.