A study analyzing pharmacy claims among patients who receive chronic medications via 3-tier prescription drug plans found that patients who were prescribed generic or preferred medications by their physicians were the most likely to adhere with their treatments.

"These findings ought to stimulate awareness of the importance of the choice of prescription when initiating therapy," stated the authors of the study, which was published in the Archives of Internal Medicine. "This study suggests that patient and physicians need to pay close attention to the formulary status of medications when prescribing to improve adherence."

Within 3-tier programs, prescriptions for generic (tier 1) or preferred brand-name (tier 2) medications generally result in lower copayments for patients. In the study, copayments ranged from $5 to $20 for generic prescriptions, $15 to $40 for preferred brand-name medications, and from $30 to $60 for nonpreferred medications.

From October 2001 to October 2002, the authors reviewed prescriptions for chronic medications among 6 drug classes—oral contraceptives, calcium channel blockers, angiontensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), statins, and inhaled corticosteroids. In total, 3,110 doctors gave 7,532 prescriptions to 6,755 patients.

The initial prescriptions were then divided into their respective tiers: 1,409 tier-1 generic medication prescriptions, 4,376 tier-2 preferred medications, and 1,747 tier-3 nonpreferred medication prescriptions.

By calculating the proportion of days covered (PDC), adherence was measured from 0% to 100% with "adequate" adherence at a PDC of 80% or greater. The authors also measured how often patients switched from their initial prescription to another drug in the same class but in a different tier.

According to the study, patients initially prescribed a tier-1 generic prescription were 62% more likely to have adequate adherence than those who were given a nonpreferred tier-3 prescription (OR=1.62; 95% CI, 1.39–1.89; P<.05). Those given a tier-2 prescription also had greater odds of adequate adherence (OR=1.30; 95% CI, 1.15–1.47; P<.05) than those with tier-3 prescriptions.

The initial prescription's formulary status also had an effect on general patient adherence. For patients initially given a tier-1 prescription, the PDC was 6.6 percentage points greater than those who received nonpreferred tier-3 prescriptions, a 12.6% increase in adherence (58.8% vs 52.2%; P<.001). Those given a tier-2 prescription had a PDC 4.6 percentage points greater than those given a tier-3 prescription, resulting in an 8.8% increase in adherence (56.8% vs 52.2%; P<.001).

Demographics that affected adherence included age—the PDC increased by 3 percentage points as patients aged 10 years (P<.001); the mean income level associated with the patient's ZIP code—those in higher-income ZIP codes had a level of adherence that was 4 percentage points greater than those in ZIP codes associated with lower incomes (P=.008); and gender—the PDC level for males was 3 percentage points greater than for females (P<.001).

When measuring the frequency of switching drugs within classes, patients were 2.8 times more likely to change from a higher-tier medication with a higher copayment to a lower-tier medication with a lower copayment. Patients given nonpreferred tier-3 medications had the greatest likelihood of changing their prescription, with 28.3% switching to tier-1 or tier-2 medications with lower copayments.

According to the authors, limitations to the study included the demographics of the patient sample. Most patients were relatively young (median age of 42.2 years) and were employed. The sample also drew from residents of just 2 states in the western United States.

Another limitation was using pharmacy claims data as the source, which eliminated patients who may have received a prescription from their physician but subsequently chose not to have it filled because of "sticker shock," likely causing an underestimation in the amount of nonadherence among patients in the study.

Despite the limitations, the study's conclusions remain valid, according to the study's lead author, William H. Shrank, MD, MSHS, division of pharmacoepidemiology and pharmacoeconomics, Brigham and Women's Hospital and Harvard Medical School, Boston, Mass.

"Generic drugs not only save money for patients and insurers, they improve the likelihood that patients will take their drugs," said Dr Shrank. "This study suggests that even greater use of generic drugs could help patients enrolled in tiered benefit plans."

SOURCE Shrank WH, Hoang T, Ettner SL, et al. The implications of choice. Arch Intern Med. 2006;166:332–337.

Tracey Walker, senior editor of Managed Healthcare Executive, a sister publication to Formulary, contributed to this article.