Use of Prescription Drug Samples in the USA: A Descriptive Study with Considerations for Pharmacoepidemiology

Abstract

Introduction Free prescription drug samples provided in physician offices can lead to exposure misclassification in pharmacoepidemiologic studies that rely on pharmacy claims data. Methods We quantified drug-specific sample provision rates based on nationally projected data from a survey of over 3200 US office-based physicians for 1993–2013. Results Between 2009 and 2013, a total of 44.7 % of newly initiated brand-only sitagliptin but only 3.6 % of generically available metformin therapy was provided as samples. We observed similar discrepancies between newly initiated rosuvastatin and simvastatin, dabigatran and warfarin, atomoxetine and methylphenidate, and between oral antibiotic drugs. During continued therapy, sample use was still present though to a lesser extent (sitagliptin 17.0 %, rosuvastatin 23.9 %), and remained high for some oral contraceptives (norethindrone 55.8 %). Oral contraceptives had the longest average days of sample supply (levonorgestrel, continued use 85.1 days). The average days of supply for all other chronically used study drugs ranged from 13.4 (dabigatran, new use) to 25.3 (exenatide, continued use) per sample provided. From 1993 to 2013, we found pronounced drops in sample provisions over time coinciding with more recent generic approval dates. Conclusions We observed markedly differential exposure to medication samples between branded and generic drugs. This can introduce bias in pharmacoepidemiologic studies, especially when adverse events that occur soon after drug initiation are of interest.

Predicting persistence to antidepressant treatment in administrative claims data: Considering the influence of refill delays and prior persistence on other medications

“…Patients receiving antidepressant samples or receiving antidepressants during hospitalization are more likely to be misclassified as non-persistent at 6-months as it would result in inaccurate dispensing dates or days supply values. The prevalence of sample use ranges by drug class and by branded vs. generic products (Hampp C et al, 2015; Li X et al, 2014). While there are not estimates of antidepressant sample use in our population, available estimates of sample use include 14% of patients with some prescription use (Alexander GC et al, 2008) and 13% of patients with a prescription for a branded statin (Li X et al, 2014).…”

Initiation of antihypertensive monotherapy and incident fractures among Medicare beneficiaries

“…Third, we repeated the primary analysis excluding beneficiaries who initiated therapy using a brand antihypertensive medication versus a generic antihypertensive medication. Generic medications are less prone to sample use and are thus less prone to have started antihypertensive therapy before the first dispensed prescription (Hampp et al 2016 ). Fourth, since chronic kidney disease and diabetes can impact physicians’ choice of antihypertensive class prescribed, we repeated the analysis removing any beneficiaries with these chronic conditions.…”

Quantification of missing prescriptions in commercial claims databases: results of a cohort study

“…They include studies using commercial claims databases to compare the proportion of subjects exposed to a specific drug in different time periods to infer missing dispensings 11 ; using the Medical Expenditure Panel Survey to quantify the degree of use of low-cost generic programs to infer the degree of missing dispensing in claims databases 12,13 ; using self-report medication use to assess lack of capture in claims databases 14 ; and examining the impact of drug samples provided by physician offices on drug exposure misclassification. 15 The magnitude of missing dispensings in those studies, not surprisingly, varies from 10% to 36%. 12,11,14 The present study offers the advantages of quantifying in millions of subjects the magnitude of missing dispensings and does it directly and objectively, because it does not rely on self report data.…”

“…These studies have used a diverse set of designs, data sources, and focus of interest. They include studies using commercial claims databases to compare the proportion of subjects exposed to a specific drug in different time periods to infer missing dispensings ; using the Medical Expenditure Panel Survey to quantify the degree of use of low‐cost generic programs to infer the degree of missing dispensing in claims databases ; using self‐report medication use to assess lack of capture in claims databases ; and examining the impact of drug samples provided by physician offices on drug exposure misclassification …”