Marjorie K. Mau, MD

As healthcare expenditures continue to rise, insurers seek to slow the rate of growth through the implementation of cost-containment measures. A common cost-containment measure is the incentive formulary, which attempts to disincentiviz

that cost-containment measures including tiered formularies

succeed in reducing overall consumption of prescription

drugs by health plan members, reducing health plan

spending on pharmaceuticals, and encouraging the choice

of less expensive over more expensive medications.

effects of cost sharing include switching to lower-cost

drugs, treatment interruptions, and taking medications less

frequently than prescribed to extend the period of use for

 The majority of studies to date have focused

on only a few therapeutic classes of drugs, most notably

angiotensin-converting enzyme inhibitors, proton pump

Diabetes mellitus, with an estimated total prevalence of 7% and medical expenditures totaling $174 billion,

 is a serious public health problem that disproportionately affects ethnic subgroups such as non-Hispanic blacks, American Indians, Alaska Natives, Native Hawaiians, and Filipinos.

 In Hawaii, the setting of this study, the prevalence of diabetes among Native Hawaiians is 11.5% and 10.4% among Filipinos.

 Although previous studies have examined the relationship between cost sharing and medication use among diabetic patients,

 to our knowledge, no studies to date have looked at the interaction between drug switching and cost sharing, an issue with potential implications for diabetes management.

To address this gap, we examined the relationship between copayment level and drug switching among patients who newly initiated a medication regime for the treatment of type 2 diabetes. The conceptual model guiding this investigation was 

the economic framework for healthcare demand proposed

 According to this framework, raising the

cost-sharing level for prescription drugs is expected to result

in (1) reduced consumption of drugs overall; (2) substitution

of less expensive, equivalent drugs; and (3) a decrease

in consumption of “nonessential” drugs (eg, discretionary

would increase the rate of switches to drugs with

lower copayments, and also that copayment levels might

have a differential effect on drug switching depending on

The design was a retrospective observational study. The study population was drawn from members of a single health plan in the state of Hawaii that provides coverage to approximately 650,000 members, or about 50% of the state’s total insured population.

 Inclusion in the study required patients to have (1) a diagnosis of type 2 diabetes and (2) a first filled prescription for a diabetes-related medication after at least 1 full year of prior enrollment. Patients were excluded if (1) they had type 1 diabetes or (2) they filled 2 different prescription diabetes medications on their first or index date. A small number of patients (n = 779) began on polytherapy and were excluded from the final study sample. Data were extracted for eligible members during the study period from January 2002 through August 2007. No universal changes in copayments occurred for this insured population during the study period. However, the study population was limited to patients who newly initiated pharmacologic treatment of their diabetes, in order to isolate “new” diabetes patients using antidiabetic medications from chronic antidiabetic medication users.

As previous studies have documented a lack of communication between patients and providers about the out-of-pocket costs for medications, we did not assume that discussions about cost occurred prior to the time the first prescription was filled.

 In addition, other studies have shown that clinicians often are unaware of the cost of different medications and therefore do not take cost into account when prescribing.

 A patient’s data were included from the date of the first prescription until the end of the study period or the end of continuous enrollment, whichever was sooner. This study was approved by the University of Hawaii Committee on Human Studies.

The medical claims database provided a limited data set on diagnoses, patient utilization, type of insurance plan (fee-for-service or HMO plan), demographic information, and morbidity levels (Johns Hopkins Adjusted Clinical Groups Case-Mix System; see www.acg.jhsph.edu) for the 3-month period preceding the index prescription.

 The pharmacy claims database provided data on medications including prescription fill dates, days of supply, copayment (out-of-pocket cost to the patient), and formulary tier. Medications were categorized by therapeutic class (all classes of oral hypoglycemics as well as insulins) within formulary tier (generic, preferred brand, and nonpreferred brand). Glycosylated hemoglobin (A1C) levels were obtained from laboratory reports from the various diagnostic laboratories. The laboratory value that most closely followed the index prescription was included in analyses. Ethnicity and education were obtained from member satisfaction surveys that are mailed annually to a random sample of the insurer’s members with response rates of 40% to 50%.

Patients were considered to have switched drugs if they discontinued use of the starting drug 

filled a prescription either (1) for a drug in a different diabetes therapeutic class or (2) for a drug in the same therapeutic class but in a different tier. Discontinuation was defined as having a gap between prescriptions greater than twice the length of the first prescription. Similarly, the study window to switch to a second drug was twice the length of the first prescription. Patients who discontinued therapy completely (ie, stopped filling their current prescription drug without adding another drug) were treated as censored from the end date of their last prescription. Gaps were calculated as the difference between the end date of the first prescription (based on the days of supply) and the fill date for the second prescription.Similar definitions of drug switching have been used inprevious studies.

Articles

Among insured patients with type 2 diabetes, copayments and glycosylated hemoglobin values were associated with increased rates of drug switching.