Generic orphan drug substitution: a critical analysis of global practices and Saudi Arabia's perspective

In an era of cost pressure, substituting generic drugs represents one of the main cost-containment strategies of healthcare systems. Despite the obvious financial benefits, in a minority of cases, substitution may require caution or even be contraindicated. In most jurisdictions, to obtain approval, the bioequivalence of generic products with the brand-name equivalent needs to be shown via bioavailability studies in healthy subjects. Rare diseases, defined as medical conditions with a low prevalence, are a group of heterogenous diseases that are typically severe, disabling, progressive, degenerative, and life-threatening or chronically debilitating, and disproportionally affect the very young and elderly. Despite these unique features of rare diseases, generic bioequivalence studies are typically carried out with single doses and exclude children or the elderly. Furthermore, the excipients and manufacturing processes for generic/biosimilar products can differ from the brand products which may affect the shelf-life of the product, its appearance, smell, taste, bioavailability, safety and potency. This may result in approval of generics/biosimilars which are not bioequivalent/comparable in their target population or that meet bioequivalence but not therapeutic equivalence criteria. Another concern relates to the interchangeability of generics and biosimilars which cannot be guaranteed due to the phenomenon of biocreep. This review summarizes potential concerns with generic substitution of orphan drugs and discusses potentially problematic cases including narrow therapeutic index drugs or critical conditions where therapeutic failure could lead to serious complications or even death. Finally, we put forward the need for refining regulatory frameworks, with emphasis on Saudi Arabia, for generic substitution and recent efforts toward this direction.

Simulated, biorelevant, clinically relevant or physiologically relevant dissolution media: The hidden role of bicarbonate buffer

In-vitro dissolution testing of pharmaceutical formulations has been used as a quality control test for many years. At early drug product development, in vivo predictive dissolution testing can be used for guidance in the rational selection of candidate formulations that best fit the desired in vivo dissolution characteristics. At present, the most widely applied dissolution media are phosphate-based buffers and, in some cases, the result of dissolution tests performed in such media have demonstrated reasonable/acceptable IVIVCs. However, the presence of phosphates in human GI luminal fluids is insignificant, which makes the use of such media poorly representative of the in vivo environment. The gastrointestinal lumen has long been shown to be buffered by bicarbonate. Hence, much interest in the development of suitable biorelevant in vitro dissolution media based on bicarbonate buffer systems has evolved. However, there are inherent difficulties associated with these buffers, such as maintaining the pH throughout the dissolution test, as CO₂ tends to leave the system. Various mathematical models have been proposed to analyze bicarbonate buffers and they are discussed in this review. Approaches such as using simpler buffer systems instead of bicarbonate have been proposed as surrogate buffers to produce an equivalent buffer effect on drug dissolution on a case-by-case basis. There are many drawbacks related to simpler buffers systems including their poor in vivo predictability. Considerable discrepancies between phosphate and bicarbonate buffer dissolution results have been reported for certain dosage forms, e.g. enteric coated formulations. The role and need of bicarbonate-based buffers in quality control testing requires scientific analysis. This review also encompasses on the use of bicarbonate-based buffers as a potentially in vivo predictive dissolution medium for enteric coated dosage forms.

Comparative pharmacokinetic and pharmacodynamic evaluation of branded and generic formulations of meloxicam in healthy male volunteers

PURPOSE

The primary aim of the present study was to assess the pharmacokinetic bioequivalence between a generic formulation of meloxicam 15 mg tablets (Meloxicam Hexal) and its respective brand product (Mobic), in order to verify whether the generic product conforms to the regulatory standards of bioequivalence in the postmarketing setting. As a secondary exploratory aim, the pharmacodynamic effects of the two formulations were also evaluated by means of rating scales following hyperalgesia induced by cutaneous freeze injury.

SUBJECTS AND METHODS

A single 15 mg dose of generic or branded meloxicam tablets was administered to 24 healthy male volunteers in a crossover fashion. Plasma samples, collected for 24 hours after dosing, were assayed for meloxicam concentration by a validated highperformance liquid chromatography method.

RESULTS

THE ANALYSIS OF PHARMACOKINETIC PARAMETERS DID NOT SHOW ANY SIGNIFICANT DIFFERENCE BETWEEN THE TWO MELOXICAM FORMULATIONS: the 90% confidence intervals fell within the acceptance range of 80%-125% (0.84-1.16 for area under the curve [0-24], and 0.89-1.23 for peak concentration). No difference in the pharmacodynamic end point was observed between the two groups.

CONCLUSION

The pharmacokinetic profiles of the two meloxicam formulations confirm the regulatory criteria for bioequivalence; pharmacodynamic data indicate a similar antihyperalgesic effect. The two formulations can be used interchangeably in the clinical setting.

Pharmaceutical equivalence by design for generic drugs: modified-release products

The Office of Generic Drugs has ensured the high quality of generic products based upon two requirements: pharmaceutical equivalence and bioequivalence to the reference listed drug (RLD). This paradigm has been used with success toward ensuring quality generic drug products that provide the same therapeutic benefit as the RLD. Drug products have increased in design complexity; as a result, approaches to ensure therapeutic equivalence must evolve to provide assurance of quality generic drug products. The Food and Drug Administration quality by design initiative (QbD) provides an enhanced evaluation approach by introducing the concept of a quality target product profile (QTPP). The QTPP introduces, within the context of the current regulatory framework, the quality concept of "pharmaceutical equivalence by design." This article illustrates through several examples how this QbD element in the evaluation of modified-release drug products enhances the current framework to ensure generic drug product equivalence. It achieves this by complementing the traditional paradigm, "equivalence by testing," where product equivalence is based upon inferences from a limited bioequivalence study, to one that also considers whether the drug product was developed to be an equivalent to the RLD, using appropriate quality surrogates that target "pharmaceutical equivalence by design."

Lack of pharmacokinetic bioequivalence between generic and branded amoxicillin formulations. A post-marketing clinical study on healthy volunteers

AIMS

There are concerns about the quality of generic drugs in the postmarketing setting. The aim was to establish whether two generic formulations of amoxicillin, available on the Italian market, fulfil the criteria for clinical pharmacokinetic bioequivalence vs. the branded drug.

METHODS

Two generic amoxicillin products (generic A and B) were selected among four fast-release tablet formulations available on the Italian market. Twenty-four healthy adult volunteers of either sex participated to a single-dose, randomized, three-treatment, crossover, single-blind bioequivalence study designed to compare generic A and B with branded amoxicillin. Plasma samples were collected at preset times for 24 h after dosing, and assayed for amoxicillin levels by high-performance liquid chromatography.

RESULTS

Ninety percent confidence intervals of AUC ratios were 0.8238, 1.0502 (ratio 0.9302) and 0.8116, 1.1007 (ratio 0.9452) for generic A and B vs. branded amoxicillin, respectively. Ninety percent confidence intervals of C(max) ratios were 0.7921, 1.0134 (ratio 0.8960) and 0.8246, 1.1199 (ratio 0.9610) for generic A and B vs. branded amoxicillin, respectively. The mean pharmacokinetic profiles showed that the AUC value of branded amoxicillin was 8.5 and 5.4% greater than that estimated for generic A and B, respectively. Few adverse events were recorded; these were not serious and occurred without apparent relationship to any specific amoxicillin formulation.

CONCLUSIONS

These results indicate that one of the two marketed amoxicillin generics analysed in the present study is not bioequivalent to the brand leader product for C(max) on the basis of single-dose pharmacokinetic assessment.

Comparing the acid-suppressive effects of three brands of generic lansoprazole with the original: pharmacokinetic bioequivalence tests do not necessarily guarantee pharmacodynamic equivalence

Generic drugs contain the same active ingredient as an original drug and have their bioequivalence proved by pharmacokinetic tests. However, few studies have been reported on whether these bioequivalence studies infer pharmacodynamic equivalence. In this study, in eight healthy Helicobacter pylori-negative CYP2C19 extensive metabolizers, we compared the acid-suppressive effects of repeated administration of 15 mg of three brands of generic lansoprazole, Taiproton, Tapizol, and Lansoral, with those of the original lansoprazole, Takepron. Median intragastric pH value for 24-h and % pH > 4 for daytime (08:00-20:00 h) and night-time were significantly higher with any lansoprazole formulation, compared with the control (P < 0.05, Wilcoxon signed-rank test). However, during the daytime, % pH > 4 with Tapizol was significantly lower than the original (P < 0.05). Compared with the original, no significantly larger, but no small range of inter-subject variations were observed in these two parameters for each of the three brands of generic lansoprazole (Bartlett test). Pharmacokinetic bioequivalence tests do not necessarily guarantee pharmacodynamic equivalence.

Equivalence-by-design: targeting in vivo drug delivery profile

In the United States (U.S.), drug products are considered therapeutically equivalent if they meet regulatory criteria of pharmaceutical equivalence and bioequivalence. These requirements can be traced back to 1977 when the U.S. Food and Drug Administration (FDA) published the regulations on bioavailability and bioequivalence. Over the years, to keep up with the advancement in science and technology, the FDA has been constantly updating the regulatory approaches to assessing and ensuring equivalence. In view of the recent growth in novel pharmaceutical dosage forms and delivery systems, this paper examines the current framework for documentation of therapeutic equivalence and explores the opportunities of further advancing equivalence methods for complex drug products. It is proposed that equivalence may be established by matching the in vivo drug delivery profile (iDDP) between drug products in comparison. This can be achieved by characterizing the iDDP of the reference formulation with application of an equivalence-by-design approach for pharmaceutical development. Critical variables can be identified to serve as in vitro markers or biomarkers for mapping the desired drug delivery profile in vivo. A multidisciplinary approach may be necessary to develop these markers for characterization of iDDPs.

Effectiveness of omeprazole- versus lansoprazole-based triple therapy for Helicobacter pylori eradication

Triple therapy with a proton pump inhibitor (PPI), amoxicillin, and clarithromycin is widely accepted for Helicobacter pylori eradication. The choice of PPI for triple therapy in Israel is arbitrary, with no preference for any one PPI except for economic considerations. Direct comparison between omeprazole and lansoprazole for efficacy of H. pylori eradication has never been performed in an Israeli poplulation. Based on the pharmacokinetic data, lansoprazole-based therapy may be a better alternative than omeprazole-based therapy. The aim of this study was to compare the effectiveness of triple therapy regimens with omeprazole (Losec, AstraZeneca; or Omeradex, Dexxon) or lansoprazole (TAP Pharmaceuticals) in eradicating H. pylori infection. The database of the biggest health insurance provider in Israel was reviewed for all patients who received 1 week of treatment with omeprazole (n = 1293) or lansoprazole (n = 85) with additional amoxicillin and clarithromycin for H. pylori eradication in 2002. All patients underwent the 13C-urea breath test (13CUBT) for validation of eradication. A negative 13CUBT result was noted in 1026 of the patients treated with omeprazole (79.4%) and 61 treated with lansoprazole (71.8%). On logistic regression analysis, none of the confounding factors (sex, age, indication, chronic use of PPI, eradication protocol) were found to contribute to the discrimination between a negative (successful eradication) and a positive (failed eradication) 13CUBT. There is no statistically significant difference between omeprazole and lansoprazole as part of a PPI-based triple therapy for eradication of H. pylori.

Comparison of proton pump inhibitor-based triple therapy with losec and the generic drug, Omepradex, for efficacy of Helicobacter pylori eradication

Triple therapy with a proton pump inhibitor (PPI), amoxicillin, and clarithromycin is widely accepted in Israel for Helicobacter pylori eradication. Recently, a generic drug for omeprazole was introduced to the market, but its efficacy as a PPI was questioned. The aim of the study was to compare eradication efficacy of triple therapy-based regimens with Losec (Astra-Zeneca, Sweden) and the generic form, Omepradex (Dexxon, Israel). People belonging to Clalit Health Services (CHS), the biggest health insurance provider in Israel, and receiving omeprazole (Losec or Omepradex) for 7 days (assumed to be Helicobacter pylori eradication purposes), between 1.1.2001 and 31.12.2001, were retrieved from the CHS central computer. Of 450 patients (287 in the Losec group and 163 in the Omepradex group), 97 (21.6%) underwent 13C-urea breath test (13CUBT) for validation of Helicobacter pylori successful eradication and participated in the study. They were all treated with triple therapy with omeprazole, amoxicillin, and clarithromycin, and were stratified according to the PPI used: Group A, Losec; and Group B, Omepradex. Positivity of 13CUBT was computed. Sixty-one (21.25%) and 36 (22.08%) patients in Groups A and B, respectively, underwent 13 CUBT for validation of successful Helicobacter pylori eradication (NS). In Group A 41 of 61 patients (67.21%) had a negative 13CUBT, in comparison with 26 of 36 (72.22%) in Group B (NS). Using logistic regression analysis all confounding factors were found to be noncontributory to the discrimination between negative (successful eradication) and positive (failed eradication) 13CUBT. There is no statistically significant difference between Losec and the generic drug Omepradex as part of a PPI-based triple therapy for eradication efficacy of Helicobacter pylori.

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.