Generic drugs in dermatology: part I

The cost of health care in the United States is increasing. In order to help control these rising costs, all parties involved in the delivery of health care, including dermatologists, need to be part of the solution of ethically reducing the cost of delivery of care. One potential means of meeting this goal is to increase the use of generic medications in daily practice. Generic medications can offer equally efficacious therapy at significantly lower prices, which can translate into large scale savings for the individual patient, the payer, and the overall health care system. Herein we provide an overview of new drug development, review the history of the generic drug industry, describe how generic drugs are approved by the US Food and Drug Administration, and define the concepts of bioequivalence and therapeutic equivalence. In part II, we explore various factors impacting generic drug use, provide cost analyses of dermatologic brand name and generic drugs, and review data addressing potential differences in the effectiveness of brand name versus generic drugs in dermatology. The cost of brand name and generic medications is highly variable by pharmacy, state, and payer. We used one source (www.drugstore.com) as an example and for consistency across all medications discussed herein. Prices included here may not reflect actual retail prices across the United States.

Bioequivalence and other unresolved issues in generic drug substitution

BACKGROUND

Substitution of generic drugs for brand-name products is highly controversial and often is met with suspicion by health care providers and patients. Historically, the debate has focused on the issue of bioequivalence, and clinical practice has identified a number of drug classes for which generic substitution should be approached with caution. Current bioequivalence requirements are based on a measure of average bioequivalence; however, there are fears that use of this measure may be inappropriate in the case of a drug with a narrow or wide therapeutic range or high intrasubject or intersubject variability. Under these circumstances, measures of individual and population bioequivalence are proposed to be more accurate than measures of average bioequivalence.

OBJECTIVE

This paper addresses issues of bioequivalence and other concerns with generic drug substitution.

METHODS

I conducted a MEDLINE search of the English-language literature containing the key terms generic, multisource, quality, and brand and published between 1973 and 2003. The names of branded pharmaceuticals whose patents had recently expired (eg, Ventolin HFA, Adalat, Capoten, Tagamet HB 200, and Valium) also were used to search for articles on generic substitution. Reference lists of relevant articles also were searched. Bioequivalence issues are presented together with more general concerns over generic drug substitution, such as consumer perception of risk, differences in product and packaging appearance, and differences in excipients.

RESULTS

The literature reviewed act to highlight a number of different drug categories and patient subpopulations for which generic substitution can still prove to be problematic.

CONCLUSION

I recommend that health care providers continue to exercise caution in the consideration of generic drug substitution under certain circumstances.

Population and individual bioequivalence: lessons from real data and simulation studies

The Food and Drug Administration (FDA) has proposed replacing the 1992 average bioequivalence (ABE) with population and individual bioequivalence (PBE & IBE), as outlined in the preliminary draft guidance of December 1997, which was subsequently replaced by the draft guidances of August 1999 and resolved in the final guidance of October 2000. This has led to considerable public debate among regulatory, academic, and industry experts at numerous conferences (e.g., FDA/AAPS March 1998, FDA/AAPS August-September 1999, FDA Pharmaceutical Sciences Advisory Committee September 1999) and in the literature. The final guidance calls for ABE to remain as the primary criterion by which new formulations may be judged ready for access to the marketplace. In addition, the FDA recommends the use of replicate study designs for the specific drug classes of controlled-release formulations and highly variable drugs. The final guidance also alludes to the possibility of a sponsor requesting alternative criteria such as PBE and IBE following consultation with the FDA. This procedure amounts to a data collection period during which data suitable to evaluate the operating characteristics of PBE and IBE would be generated, analyzed, and discussed among interested parties. A comprehensive review of currently available databases is useful in determining the ultimate value of this data collection period. This report provides an update to the previous publication by the authors. In all, 28 data sets from 20 replicate cross-over bioequivalence studies have been analyzed (n = 12-96) using the statistical methodology in the most recent FDA draft guidance. The results are presented below. ABE Pass: ABE Fail: Total: AUC/Cmax AUC/Cmax AUC/Cmax AUC/Cmax Pass PBE & IBE 20/14 1/3 21/17 Pass IBE only 1/0 0/0 1/0 Fail PBE and IBE 0/2 0/1 0/3 Fail IBE only 2/3 4/5 6/8 Total 23/19 5/9 28/28 Review of the database reveals many interesting features, most notably the lack of consistent results within a given data set across all three criteria. The sensitivity of subject-by-formulation interaction to sample size and inherent variability of the compounds is further explored through simulation studies. It is concluded that additional simulation assessments must be considered when evaluating the value of a data collection period for PBE and IBE assessment. It will be shown that definitive conclusions regarding some of the operating characteristics of PBE and IBE can be achieved through a combination of data-driven hypotheses followed by simulation studies to further evaluate the hypotheses. Some recommendations for further data collection will be made.