Bioequivalence assessment of generic drugs: an American point of view

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.

Generics and cost-effective prescribing in Belgium: does bioequivalence always translate in therapeutic equivalence?

As many other countries, Belgium has a policy to promote the use of generic pharmaceutical products. In order to protect consumers, these generic products must be demonstrated to be essentially similar to the previously approved product, typically an innovator product. The therapeutic equivalence of a generic and an innovator product is most commonly based on the demonstration of bioequivalence, i.e. clinically insignificant differences in the rate and extent of drug absorption usually assessed from pharmacokinetic measurements, in a normal and healthy population. This article reviews the bioequivalence requirements for generic products and examines whether bioequivalence always adequately substantiates therapeutic equivalence and interchangeability. 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. There are fears that use of this measure may be inappropriate in the case of a drug with a narrow 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. Bioequivalence issues are discussed together more general concerns about generic drug substitution, such as differences in product and packaging appearance and differences in excipients.

Bioequivalence testing of a new tablet formulation of generic fluoxetine

The pharmacokinetics and relative bioavailability of fluoxetine capsules (reference) and tablets (test) were compared in 24 healthy subjects of both sexes after a single 20 mg oral dose of fluoxetine (as a hydrochloride salt). A randomized, crossover design with a 2-week wash-out period between each dose was applied. Serum samples, obtained before dosing and at various appropriate time points up to 192 hours, were analyzed for fluoxetine and norfluoxetine content by a simple, accurate and precise HPLC method. ANOVA, power analysis, 90% confidence intervals (CI), and two one-sided tests were used for the statistical analysis of pharmacokinetic parameters. The tolerability of the preparations was good. The respective point estimates of the ratios of the geometric means of log-Cmax and log-AUC(0-infinity) of fluoxetine were 0.912 and 0.935 with 90% of 0.838-0.992 and 0.857-1.020. The corresponding point estimates of norfluoxetine were 0.952 (90% CI = 0.843-1.075) and 0.904 (90% CI = 0.807-1.013), respectively. Since both 90% CI for the AUC(0-infinity). and Cmax geometric mean ratios of fluoxetine and norfluoxetine were included in the 80% to 125% interval proposed by the FDA the test drug (fluoxetine tablets) was considered bioequivalent to the reference one (Prozac capsules) according both to the rate and extent of absorption.

A randomized, open-label pharmacokinetic comparison of two oral formulations of fluconazole 150 mg in healthy adult volunteers

BACKGROUND

Because of its systemic action, fluconazole is prescribed for a variety of fungal infections. However, therapeutic failure might result when a patient is switched between an innovator drug and a nonbioequivalent generic formulation. Pharmacokinetic (PK) studies investigating the bioequivalence of generic and innovator drugs can minimize such risks.

OBJECTIVE

The aim of this study was to compare the PK profiles and relative bioavailabilities of 2 oral formulations of fluconazole: Diflucan (reference; Pfizer Corporation Austria GmbH, Wien, Austria) and Funzol (test; Bosnalijek d.d., Pharmaceutical and Chemical Industry, Sarajevo, Bosnia and Herzegovina), both prepared as capsules containing 150 mg of active drug.

METHODS

A single oral dose of fluconazole was given under fasting conditions to healthy, white volunteers aged 18 to 55 years in this open-label, randomized, crossover study. A 3-week washout period was applied between each of the 2 doses. Serum samples were obtained before dosing and at various time points after dosing up to 144 hours and were analyzed for fluconazole concentration using a high-performance liquid chromatography-UV method. PK parameters representing the extent (AUC(0-infinity)) and rate (CmaX and T(max)) of absorption of fluconazole were obtained. An analysis of variance, a power analysis, 90% CI, and two 1-sided tests were used for statistical analysis of relative differences between the 2 drugs. Bioequivalence was concluded if the 90% CIs for the geometric mean ratios of AUC(0-infinity) and C(max) were between 0.80 and 1.25. A study investigator monitored the volunteers for adverse effects at 5 defined time points during the clinical part of the investigation.

RESULTS

Thirteen men and 11 women (mean age, 33.3 years; mean weight, 73.6 kg) completed the study. The respective point estimates of the ratios of geometric means of log-transformed C(max) and AUC0(0-infinity) of fluconazole (test vs reference) were 0.985 and 1.047, with 90% CIs of 0.894 to 1.085 and 0.927 to 1.182, respectively. Differences in T(max) also did not reach statistical significance. No adverse effects were reported by the subjects or revealed by clinical or laboratory tests.

CONCLUSIONS

The study failed to demonstrate any statistically significant differences in C(max) and AUCO(0-infinity) values between the test and reference formulations of oral fluconazole 150 mg in this small, select population of healthy volunteers. On that basis, and according to both the rate and extent of absorption, the test and reference formulations were considered bioequivalent.

Individualizing therapy - in search of approaches to maximize the benefit of drug treatment (II)

Adjusting drug therapy to the individual, a common approach in clinical practice, has evolved from 1) dose adjustments based on clinical effects to 2) dose adjustments made in response to drug levels and, more recently, to 3) dose adjustments based on deoxyribonucleic acid (DNA) sequencing of drug-metabolizing enzyme genes, suggesting a slow drug metabolism phenotype. This development dates back to the middle of the 20^th century, when several different drugs were administered on the basis of individual plasma concentration measurements. Genetic control of drug metabolism was well established by the 1960s, and pharmakokinetic-based individualized therapy was in use by 1973.

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.

Report of the American Society of Transplantation conference on immunosuppressive drugs and the use of generic immunosuppressants

Considerable economic and health-related costs are associated with the life-long maintenance immunosuppressive therapy required to prevent transplant rejection. Generic medications have the potential of providing equivalent therapeutic efficacy at a lower economic cost. In 2001, the American Society of Transplantation invited experts to review the data and issues associated with the approval and use of generic immunosuppressants. A summary of that meeting is reported here. The generic medication approval process has been in effect for more than 30 years. All marketed generic cyclosporin formulations have met FDA criteria demonstrating bioequivalence in healthy subjects, and some were also tested in transplant recipients. Most participants agreed that generic narrow therapeutic index immunosuppressive agents provide adequate de novo immunosuppression in low-risk transplant recipients. However, some participants expressed concern regarding the currently unquantified risk that may be associated with switching immunosuppressive agents under uncontrolled circumstances. There was broad agreement among the participants that generic medications should be clearly labeled and distinguishable from innovator drugs, and that patients should be educated to inform their physicians of any switch to or among generic alternatives. There was also strong support in favor of requiring studies to demonstrate bioequivalence in potentially at-risk patient populations, specifically African-Americans and pediatric patients.

Understanding the scientific issues embedded in the generic drug approval process

OBJECTIVE

To review the major scientific issues embedded in the generic drug approval process.

DATA SOURCES

Articles indexed initially under terms such as generic medications, generic drugs, bioequivalence, and bioinequivalence. These terms were used to search indexing services such as MEDLINE, International Pharmaceutical Abstracts, CINAHL (a database of nursing and allied health literature), and Science Citation Index. Additional data sources included the Code of Federal Regulations and regulatory guidances from the Food and Drug Administration (FDA) Center for Drug Evaluation and Research.

STUDY SELECTION

Performed by the authors.

DATA EXTRACTION

Not applicable.

DATA SYNTHESIS

Despite the fact that regulations regarding bioequivalence have been in place for more than 20 years, controversies over bioequivalence continue to arise. Consensus on many of these issues is driving the development of new FDA guidances regarding bioequivalence. Still, despite the issuance of new guidance and consensus building among scientists, many clinicians and consumers remain uninformed regarding the scientific basis for establishing bioequivalence and the generic drug approval process in general. Although some have suggested that the generic drug approval process is flawed, overall, it appears that the process works.

CONCLUSION

Understanding the generic drug approval process and the issues surrounding bioequivalence is of paramount importance to both clinicians and scientists.

Management of narrow therapeutic index drugs

Summary. Narrow therapeutic index (NTI) drugs are agents for which small changes in systemic concentration can lead to significant changes in pharmacodynamic response. This may result in potentially subtherapeutic or toxic effects, particularly in patients with advanced age, comorbid illness, or those receiving multiple medications. Bioequivalence among generic and innovator drug products does not always ensure therapeutic equivalence, especially with regard to NTI drugs. Warfarin is a NTI drug for which substitution is now available and may occur routinely without the knowledge of the patient or practitioner. To avoid overanticoagulation or underanticoagulation, the additional cost of patient education and monitoring may actually exceed cost savings by using the less expensive generic drug product. When brand name drug is preferred by the practitioner, "no substition" must be specified on the prescription to avoid mandated generic interchange of warfarin and other NTI drugs.

Drug substitution in transplantation: a National Kidney Foundation White Paper

Specific safeguards to guide the approval process and substitution practices for generic immunosuppressive agents are necessary for the effective delivery of patient care. Currently, the Food and Drug Administration (FDA) requires the demonstration of bioequivalence of generic drugs to innovator drugs in normal healthy subjects, a criterion that may be insufficient for critical-dose drugs. For generic equivalents of critical-dose drugs and for innovator critical-dose drugs, there should be a requirement for replicate studies measuring intrasubject variability and subject-treatment interactions to establish that bioequivalence holds true. Extensive testing of generic drugs in all target patient types is impractical and should not be required. However, when evidence suggests that the bioavailability of a critical-dose drug may vary substantially in certain subgroups, the FDA should require a demonstration of bioequivalence of generic versions to innovator products in these representative target populations. Changes in the approval process for generics should be accompanied by more consistent substitution practices. Pharmacists should notify the prescribing physician and patient whenever a critical-dose drug (generic or brand name) is dispensed in a different formulation from the one the patient has been taking. Therapeutic substitution for such drugs should not be made unless the prescribing physician has granted approval. The health care provider should consider instituting appropriate monitoring whenever patients are switched between generic formulations or between innovator drugs and generic formulations. Patients should be well informed about generic substitutes so that they can participate in treatment choices.

Cubic spline functions and polynomials for calculation of absorption rate

A model-independent method for calculation of the absorption rate based on an exact mathematical solution to the deconvolution problem of systems with linear pharmacokinetics and a polyexponential impulse responses has been examined. Theoretical analysis shows how a noninteracting primary input can be precisely evaluated when data on blood levels from a known source such as an i.v. bolus or zero-order infusion are available. This work compares the use of a Lagrange 3rd degree polynomial with that of a cubic spline function (special 3rd degree polynomial) for calculation of the absorption rate. The method is compared to another using simulated data (12 data points) containing various degrees of random noise.The accuracy of the methods is determined by how well the estimates represent the true values. It was found that the accuracy of the two methods was not significantly different, and that it was of the same order of magnitude as the noise level of the data.