Effect of Medication Burden on Persistent Use of Lipid-Lowering Drugs Among Patients With Hypertension

This study assesses the effect of medication burden on persistent use of newly added lipid-lowering drugs among patients with hypertension.

Published Online: November 14, 2008
Teisha A. Robertson, PharmD, MBA; Catherine E. Cooke, PharmD, BCPS; Jingshu Wang, PhD; Fadia T. Shaya, PhD, MPH; and Helen Y. Lee, PharmD, MBA

Objective: To determine the effect of medication burden on persistent use of newly added lipid-lowering (LL) drugs among patients with hypertension.

Study Design: This retrospective database study used medical and pharmacy claims from a mid-Atlantic managed care organization. The cohort was obtained from continuous member enrollment in pharmacy and medical benefits from January 1, 2003, to December 31, 2005.

Methods: Prescription claims were obtained for 18 months following the date of the first filled LL prescription (ie, index date). Patients were stratified into patients who changed LL drug or strength (group 1) and patients who did not change LL drug or strength (group 2). The primary outcome measure was persistence to newly added LL therapy. Persistence was defined by the length of time a member remained on therapy following the index date. The secondary outcome measure was the medication possession ratio (MPR). The MPR was calculated as the ratio of the sum of the days’ supply of prescription filled divided by the number of days filled, plus the days’ supply for the final prescription fill. Associations between the daily medication burden, defined as the number of unique drug products, and the outcome measures were analyzed.

Results: In the cohort of 3058 patients, the mean medication burden was 2.9 medications. Medication burden was positively associated with persistence and MPR through 18 months. Patients who had greater medication burden had longer persistence (P <.001). Likewise, patients who had greater medication burden had higher MPRs and  were more likely to be considered adherent (MPR, =80%) (P < .001 for both).

Conclusions: Patients with higher medication burden had greater adherence to newly added LL therapy. Medication burden should not deter clinicians from adding LL therapy. Among patients with added LL therapy, more attention should focus on patients who have changes to their LL regimen compared with patients who continue on the same LL prescription.

(Am J Manag Care. 2008;14(11):710-716)

Cardiovascular risk factors such as hypertension and dyslipidemia commonly coexist, requiring the patient to use multiple drug therapies to achieve optimal control according to guidelines.

  • Clinicians managing patients often struggle with adding more drugs to regimens of patients
    who already have complicated medication regimens.
  • This study describes the effect of medication burden on persistent use of newly added
    lipid-lowering drugs among patients with hypertension.
  • Patients with higher medication burden had greater adherence to newly added lipid-lowering therapy; therefore, medication burden should not deter clinicians from adding lipidlowering therapy.
Cardiovascular disease (CVD) continues to be the leading cause of morbidity and mortality in the United States.1,2 In 2002, CVD in the United States accounted for 1.4 million deaths.1,2 Annual direct and indirect costs of CVD in 2007 were estimated to be approximately $431.8 billion.1,2 Several factors increase the risk of CVD such as hypertension, age (>55 years for men and >65 years for women), dyslipidemia, diabetes mellitus or glucose intolerance, renal dysfunction, family history of premature CVD (relative’s age <55 years in men and <65 years in women), obesity, physical inactivity, and smoking.3 Studies have shown that CVD risk factors coexist. Patients with hypertension often have 1 or more concomitant risk factors, including diabetes mellitus or glucose intolerance, obesity, and dyslipidemia, all components of the metabolic syndrome.4,5 Less than 20% of patients with hypertension have no other CVD risk factors.4 Two of the most prevalent and asymptomatic risk factors for CVD, hypertension and dyslipidemia, commonly coexist, and the risk of CVD associated with having both is greater than the risk associated with having hypertension or dyslipidemia alone.4,6 The US Third National Health and Nutrition Examination Survey provides an estimated prevalence of concomitant hypertension and dyslipidemia of about 15% among adults, which equates to approximately 30 million adults in the United States.7

The National Cholesterol Education Program Adult Treatment Panel III guideline recommends aggressive management of patients with concomitant hypertension and dyslipidemia.8 Meta-analyses and clinical trials have found that antihypertensive and lipid-lowering (LL) medications significantly reduce the risk of CVD and all-cause mortality among patients with CVD risk factors.9-12

Medication therapy for the treatment of hypertension and dyslipidemia is becoming more challenging, as more than two-thirds of patients require 2 or more antihypertensive drugs and an LL drug, with high-risk patients requiring 2 or more LL drugs to achieve optimal blood pressure and cholesterol levels.3,8,13 Adequate adherence to medication regimens is essential to decrease the risk for hospitalization and healthcare expenditures.14 Poor adherence to antihypertensive and LL regimens can accelerate the development of CVD, which can lead to a decreased quality of life and premature death.3 The medication burden of patients with CVD risk factors can be high and may affect medication adherence; however, conflicting assessments have been reported. Some investigators have reported an increase in adherence among patients with higher medication burden, while others have reported the opposite result.15-20 Given the need to manage patients at high risk for CVD with multiple medications, it is important to elucidate the true effect of the number of medications on adherence.

A retrospective study of medical and pharmacy claims was performed to evaluate this. The objective was to assess the effect of medication burden on persistence of newly added LL drugs among patients with hypertension.

Methods

Data Sources and Patients

This retrospective database analysis used medical and pharmacy claims from a mid-Atlantic managed care organization serving more than 1.2 million members with medical and pharmacy benefits. The cohort included members with continuous enrollment of pharmacy and medical benefits from January 1, 2003, to December 31, 2005. Members were included in the analysis if they had at least 1 International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) code for hypertension (401.xx) from January 1, 2003, to June 30, 2004, and at least 1 prescription for an LL drug dispensed between July 1, 2003, and June 30, 2004. Members were excluded from analysis if they had any of the following: prescriptions for LL therapy before the first ICD-9- CM code for hypertension in the study period; LL prescriptions dispensed from January 1, 2003, to June 30, 2003; age younger than 18 years on the index date (ie, the date of the first filled LL prescription); more than 1 prescription for an LL drug filled on the index date; an LL prescription with negative days’ supply (a void in the prescription and the patient did not receive the drug); only 1 filled LL prescription during the study period; or ICD-9-CM diagnosis codes from January 1, 2003, to December 31, 2005, for comorbid diseases, including HIV, cancer, dementia, Alzheimer’s disease, mental retardation or Down syndrome, schizophrenia, bipolar disorder, or depression, that could affect adherence (Figure).

The first filled LL drug during the study interval was considered the index prescription. Patients included in the study had the same observation period of 18 months following the index date. Prescription claims were obtained for patients included in the cohort for 18 months following the index date. To assess for differences among patients who change or switch from 1 drug to another or change the dosage of their medication versus patients who remained on the same medication and dosage, patients were stratified into 2 groups. Group 1 included patients who changed LL drug (including patients who switched to a different strength of the same drug or to a different class of the drug, as well as patients who added an LL drug). Group 2 included patients who did not change LL drug or strength (ie, had the same prescription throughout the study).

Lipid-lowering drugs included all those on the US market during the study period, including bile acid sequestrants, statins, fibric acid derivatives (fibrates), cholesterol absorption blockers, combination therapy of 2 medications in 1 formulation, and others (eg, niacin). Data from medical and pharmacy claims included unique deidentified patient number, patient’s age on the index date, sex, disease diagnoses as defined by ICD- 9-CM codes, prescription information for all filled LL drugs (drug name, prescription fill date, days’ supply, and copayment), and a list of concurrently filled prescription medicines 6 months before and within 6 months after the index date.

Outcome Measures

Medication adherence was evaluated based on persistence and the medication possession ratio (MPR). The primary outcome measure, persistent use of an LL drug, was specified as the length of time in days that patients remained on an LL drug following the index date. A patient was deemed persistent if he or she filled a prescription within a grace period of 30 days from the end of the days’ supply of the prior prescription.21-23 For patients who had changes to their index LL regimen (group 1), persistent use of the index LL prescription and persistent use of the switched LL prescriptions were combined. Persistence was truncated to 548 days (18 months) for patients with LL prescriptions that extended beyond the 18-month study period. The secondary outcome measure, MPR, was calculated as the ratio of the sum of the days’ supply of prescription filled by the patient divided by the number of days from the fill date of the index prescription to the last fill date, plus the days’ supply for the final prescription fill.24 For patients who had changes to their index LL regimen, the sum of the days’ supply of the index LL drug was added to the sum of the days’ supply of the changed LL drugs, divided by the number of days from the fill date of the index prescription to the last fill date of the changed LL drugs, plus the days’ supply for the final prescription fill. The MPR was truncated to a ratio of 1 for patients with a sum of days’ supply of filled LL prescriptions exceeding 548 days. Patients were deemed to be adherent if the MPR was at least 80%, a cutoff percentage that is frequently cited in the literature.25

Operational Definition of Medication Burden

The medication burden was defined as the number of unique drug products. The number of unique drug products was determined by averaging the covered medications taken chronically (>90 days) for which the days’ supply of the medication overlapped or was within 30 days after the end of the days’ supply of the index prescription. This definition excludes medications prescribed for acute treatment (eg, anti-infective drugs and cough and cold drugs) during the study period (eAppendix available at www.ajmc.com). As an example, for a patient who filled a prescription for simvastatin on March 20, 2004 (index date), the patient’s medication burden would be assessed as follows: lisinopril (20 mg) filled with a 30-day supply on March 1, 2004, would count as a unique drug product; alendronate sodium (70 mg) filled with a 90-day supply on April 15, 2004, would count as a unique drug product; metformin (1000 mg) filled with a 30-day supply on March 20, 2004, would count as a unique drug product; and amoxicillin (500 mg) with a 10-day supply on March 15, 2004, would not count as a unique drug product. The medication burden for the patient would be 3 medications.

Statistical Analysis

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