Prevalence of Low-Cost Generic Program Use in a Nationally Representative Cohort of Privately Insured Adults

AUTHORS: Nathan James Pauly, Joshua David Brown

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SUMMARY:

BACKGROUND:Administrative claims data are used for a wide variety of research and quality assurance purposes. Despite their utility, they are prone to medication exposure misclassification if medications are purchased without utilizing an insurance benefit. Low-cost generic programs (LCGPs) offered at major chain pharmacies are a relatively new and sparsely investigated source of exposure misclassification. Since they were implemented in 2006, LCGPs are now available at 8 of the 10 largest pharmacy chains and include a wide variety of medication classes. LCGP medications are often purchased out of pocket; thus, a pharmacy claim may never be submitted and exposure may go unobserved in claims data. There are little data regarding the utilization of these programs, and estimates of their use can provide important insights into the potential impact LCGPs may have on exposure misclassification in claims data.

OBJECTIVES: To (a) quantify the prevalence of LCGP users in a privately insured adult population, (b) assess patterns of LCGP use, and (c) compare clinical and demographic characteristics associated with LCGP users and nonusers. 

METHODS: The study cohort consisted of 19,037 privately insured adults aged 18-64 who participated in the Medical Expenditure Panel Survey (MEPS) from 2007-2011. MEPS captures medication utilization at the pharmacy level, so prescription fills can be observed irrespective of a claim being filed. Pharmaceutical utilization was assessed at the individual level for each year of the study period, and LCGP use was recorded as a binary variable for each individual. An LCGP medication fill was identified if the total cost of the drug was paid out of pocket and matched the cost of medications listed on LCGP formularies available from Target, Walmart, CVS, or other major pharmacy retailers during these years. Cohort demographics and characteristics of interest included age, gender, race, employment
status, marital status, family income, education level, residence in a
metropolitan statistical area (MSA), prescription drug coverage, geographic region, comorbidities, and number of unique medications and medication fills. Comparisons were made between users and nonusers using chi-square and t-tests. Multivariable logistic regression was used to identify factors associated with LCGP use.

RESULTS: Out of the entire study cohort (N = 19,037), 6,921 (36.4%) individuals were identified as LCGP users, representing 34 million LCGP users annually. Users tended to be older, had higher Charlson Comorbidity Index scores, filled more prescriptions per person, and used more unique medications. Proportions of LCGP users and uses nearly doubled from 2007-2011, while total prescription utilization per person remained relatively stable. Over 10% of all prescription fills were filled through LCGPs. Of all LCGP fills, approximately 42% were for cardiovascular medications, 12% for antidiabetics, and 14% for levothyroxine. Greater than 30% of fills for antigout, metronidazole, angiotensin-converting enzyme inhibitors, levothyroxine, metformin, and diuretics were obtained through LCGPs, as were 18.9% of all warfarin fills. Compared with the reference category aged 18-34, adults aged 35-54 had an adjusted odds ratio (AOR) of being an LCGP user of 1.39 (95% CI = 1.29-1.50) and adults aged 55-64 had an AOR of 1.86 (95% CI = 1.70-2.04). Additionally, those with prescription drug coverage were nearly twice as likely to be LCGP users (AOR = 1.96; 95% CI = 1.64-2.35) compared with those without. Gender, income, comorbidity burden, region, year of panel entry, and number of unique medications also significantly predicted LCGP use.

CONCLUSIONS: There is a high rate of LCGP use in the privately insured adult population. Users of LCGPs tend to be older, have more chronic comorbidities, and use more medications than nonusers. Claims-based research and quality assurance programs focusing on the benefits and harms of medications available through these programs are at risk of greatly underestimating the true medication exposure in this population and should account for this in sensitivity analyses. Managed care organizations should incentivize the reporting of LCGP medication use or make adjustments to generic medication benefit structures to more effectively capture true medication exposure.

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