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

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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.

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The views expressed herein do not necessarily represent the views of the US FDA or the US Government.

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Authors and Affiliations

  1. Division of Epidemiology-I, Office of Pharmacovigilance and Epidemiology, Office of Surveillance and Epidemiology, Center for Drug Evaluation and Research, US Food and Drug Administration, 10903 New Hampshire Avenue, Silver Spring, MD, 20993, USA

    Christian Hampp & Simone P. Pinheiro

  2. Division of Epidemiology-II, Office of Pharmacovigilance and Epidemiology, Office of Surveillance and Epidemiology, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, MD, USA

    Patty Greene

Authors
  1. Christian Hampp
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  2. Patty Greene
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  3. Simone P. Pinheiro
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Correspondence to Christian Hampp.

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Funding

No sources of funding were used to assist in the preparation of this study.

Conflict of interest

Christian Hampp, Patty Greene, and Simone Pinheiro have no conflicts of interest that are directly relevant to the content of this study

Ethical standards

The study was exempted from review by the FDA Research Involving Human Subjects (RIHSC) committee under 45 CFR 46 101(b)(4).

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Hampp, C., Greene, P. & Pinheiro, S.P. Use of Prescription Drug Samples in the USA: A Descriptive Study with Considerations for Pharmacoepidemiology. Drug Saf 39, 261–270 (2016). https://doi.org/10.1007/s40264-015-0382-9

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