Date of Award

2003

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Pharmaceutical Sciences

First Advisor

Paul Larrart

Abstract

Many health maintenance organizations (HMOs) have implemented programs providing varying degrees of annual drug coverage for Medicare beneficiaries enrolled in their plans. Older adult plan members in an HMO operating in central Massachusetts were able to choose among 3 drug benefit options starting January 1, 1994: full coverage for prescription drugs, a maximum of $1000/year in coverage, or no drug coverage. As such, cost containment policies have been shown to affect prescription drug use and other types of health service utilization. The unintended effects of this policy are important to consider. This research investigated the effects of type of drug benefit plan chosen on use of lipid lowering agents (LLA), a group of drugs of well documented benefit for both primary and secondary prevention of coronary heart disease (CHD), which continues to be a leading cause of death in the United States and worldwide.

The objectives of this study were a) to describe LLA utilization during a one year period, for both prevalent and new users, and to compare this utilization with various patient characteristics including gender, age group, prescriber specialty, comorbidities (CHD, diabetes, hypertension), and choice of drug benefit plan option; b) to examine differences in persistence to LLAs among members of different drug benefit plans; c) to determine the effect of drug plan benefit option on the type of statin drugs, a class of LLAs, prescribed (expensive versus the less expensive statins).

Analyses were performed using 2229 seniors who were continuously enrolled between July 1, 1993 and June 30, 1996 and had a prescription for an LLA. Of these, 1551 were studied to describe the LLA utilization during a one-year period (paper1), 322 to examine persistence to LLA (paper2), and 484 to investigate the type of statin prescribed (paper3).

Statins were the most widely prescribed group of LLAs among both prevalent (61.8%) and new (65.5%) users, and a very low rate of combination therapy was found in both prevalent (1.6%) and new (0.9%) users of LLAs. This may, in part, explain why many patients on LLAs do not reach their target cholesterol levels since combination therapy is more effective than monotherapy in lowering cholesterol levels.

The type of drug benefit plan option did not affect choice among LLAs, but comorbidities, mainly CHO and diabetes, seem to be among the main factors that influenced drug selection, possibly through affecting lipid levels. Patients with CHD were more frequently prescribed statin monotherapy (p=0.0001 in prevalent use; p=0.0028 in new use) and combination therapy (p=0.0467 in prevalent use) and less frequently prescribed bile acid sequestrants (p<0.0001 for prevalent use). Diabetic patients more frequently used fibrates (p=0.0032 for prevalent use), less frequently used bile acid sequestrants (p=0.0007 for prevalent use; p=0.0329 for new use), and niacin (p=0.0336 in prevalent use) compared to nondiabetics.

Other observed differences include: females were more frequently prescribed bile acid sequestrants compared to males (p=0.0213 for prevalent use; p=0.0168 for new use), which could be a result of confounding by diabetes since the significant difference disappeared after restricting the analysis to diabetics or non-diabetics. Cardiologists prescribed bile acid sequestrants more frequently (p=0.0092 for prevalent use) than internists, and finally patients aged 65-69 were less frequently prescribed a bile acid sequestrant compared to other age groups (p=0.0006 in prevalent use).

The overall discontinuation rate for LLAs increased with time from 18.3% after 6 months of therapy, to 46.4% at 12 months, to 66.3% at 18 months.

Statin users had better persistence than non-stating users in the bivariate (p=0.0004) and multivariate (HR=0.536; CI=0.375-0.766; p=0.0006) models. In the bivariate models, males had better persistence than females (p=0.0078), and CHD patients had better persistence than non-CHD patients (p=0.0424), but no significant differences with regard to gender or CHD existed after controlling for covariates in the multivariate model. No significant differences existed with plan type in the bivariate model (p=0.3121) or multivariate model (HR=0.877; CI=0.610-1.260; p=0.4777). Other variables, diabetes, other medications ≥3, age ≥70, were not significantly associated with persistence as well.

There was no significant association between the drug benefit plan option and statin type prescribed (OR=0.654; CI=0.376-1.139; p=0.1335) after controlling for potential confounders including gender, age ≥70, comorbidities (CHD, diabetes, hypertension), and physician prescriber specialty. There were no significant associations with other predictor variables as well.

In sum, research results generally indicate that the policy of drug benefit plan option initiated at the HMO among older adult members did not significantly influence the choice among or persistence to LLAs.

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