Subsequent Prescribing of New Drugs: Drug Variables

7 May

The drugs, or compounds, in clinical trials are classified by an indication based on the International Classification of Diseases, Ninth Revision (ICD-9) coding system. All of the drugs that we examined in our study represented new molecular entities (NMEs), or substantial reformulations of an existing drug. We required the re-formulations (e.g., extended-release) to be complete, original New Drug Applications (NDAs) that had been filed with the FDA. The compounds in the study came to market between 1997 and 2000. Several of the study compounds had never been submitted by the sponsoring company for FDA approval or had not received FDA approval by 2000. These compounds could not be included in the analysis. A complete list of study compounds is presented.

The clinical studies selected for use in the analysis included investigation of 38 compounds in phase 3 clinical trials that were investigated for the outpatient treatments of asthma and allergic rhinitis, hypertension, osteoarthritis and rheumatoid arthritis, depression, pneumonia, hypercholes-terolemia, and diabetes. These indications were selected for two reasons:
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  • They are outpatient indications, and the prescribing database contains prescriptions filled at the retail level.
  • They continue to receive a substantial amount of funds for research and development (R&D).

manufacturers created the USC in 1975. The system uses five digits to standardize and categorize all U.S. pharmaceuticals according to product type. USCs, which are used in the U.S. and Canada, have four levels of hierarchy. USC2 is the broadest category, and USC5 is the most detailed category, allowing for more specificity within a category. Our study used the USC5 level of specificity. (For more information on USC levels, see page 702 of the November 2004 issue of P&T.) IMS Health also indicates whether a new drug represents a new drug class, based on a new mode of action.

Dependent Variables

Study drug prescribing was reported at three, six, and 18 months after product launch, as determined by the date of the first filled prescription recorded by IMS Health, Inc. The IMS Health prescribing database tracks the retail fulfillment prescribing behavior of virtually every practicing American physician, recording more than 70% of all prescriptions filled in the U.S. The database does not include prescriptions filled by hospital pharmacies or hospital systems such as the Veterans Health Administration.

The prescribing share percentage for an individual drug by an individual physician is measured in a Uniform System of Classification (USC) share. The USC share is the percentage of the physician’s prescriptions in the corresponding drug class that are represented by that physician’s actual number of prescriptions for the study drug in question.

Statistical Methodology

Contains both means and shows standard deviation (SD) and percentages. Contain percentages, with levels of statistical significance derived from an analysis-of-covariance model. An illustrative analysis-of-covariance model, addressing new drug prescribing three months after product launch, is presented.

We used SPSS for Windows, Version 12 (SPSS Inc., Chicago, IL), to perform the analyses.