Feasibility of biowaiver extension to biopharmaceutics classification system class III drug products: cimetidine

BACKGROUND: The extension of biowaivers (drug product approval without a pharmacokinetic bioequivalence study) to drugs belonging to Class III of the Biopharmaceutics Classification System (BCS) is currently a subject of much discussion. OBJECTIVES: To assess the relationship between in vitro dissolution characteristics and in vivo absorption performance of immediate-release (IR) products containing cimetidine, a BCS Class III compound, in human subjects. To evaluate the feasibility and appropriateness of an extension of the biowaiver concept to BCS Class III compounds. STUDY DESIGN AND PARTICIPANTS: BCS-conform dissolution tests were carried out on ten marketed cimetidine products from Thailand and Germany, as well as cimetidine tablet formulations containing cimetidine 400mg manufactured by direct compression using methacrylate copolymer (Eudragit) RS PO) as a release-retarding agent to yield three batches with significantly different release profiles. Twelve healthy male subjects were enrolled in a randomised, open-label, single-dose schedule based on a five-way Williams' design balanced for carryover effects. Subjects received the following treatments, with 1-week washout periods between: (i) Tagamet 400mg tablet; (ii) 7.5% methacrylate copolymer cimetidine tablet; (iii) 15% methacrylate copolymer cimetidine tablet; (iv) 26% methacrylate copolymer cimetidine tablet; and (v) Tagamet (300 mg/ 2 mL) intravenous injection. The area under the plasma concentration-time curve from 0 to 12 hours (AUC(12)) and AUC from time zero to infinity (AUC(infinity)), peak plasma concentration (C(max)), absolute bioavailability (F) and mean residence time (MRT) were evaluated and statistically compared among formulations. In vitro-in vivo correlation (IVIVC) analysis was then applied to elucidate the overall absorption characteristics of each tablet formulation. RESULTS: The release properties of the ten marketed cimetidine products were shown to comply with current US FDA criteria for rapidly dissolving drug products. As expected, the in vitro dissolution profiles of the cimetidine tablets containing different percentages of methacrylate copolymer differed considerably from one another. However, in vivo results showed no significant difference in AUC(12), AUC(infinity), C(max) and F between the tablets manufactured with methacrylate copolymer and the innovator. The MRT values obtained from 26% methacrylate copolymer tablets were significantly longer than for the other two methacrylate copolymer formulations and the Tagamet tablets. Furthermore, IVIVC analysis showed that the 26% methacrylate copolymer tablets exhibited dissolution rate-limited absorption, whereas the other formulations showed permeability rate-limited absorption. CONCLUSION: The results of the present study indicated that the absorption of cimetidine from IR tablets is, in general, limited by permeability rather than dissolution. IVIVC analysis demonstrated that only when the release was deliberately retarded (tablets containing 26% methacrylate copolymer), did the dissolution represent the rate-limiting step to drug absorption. On the in vitro side, it seems that 85% dissolution within 30 minutes, as currently required by the US FDA Guidance, is more than sufficient to guarantee bioequivalence of IR cimetidine products. For cimetidine and other BCS Class III drugs with a similar intestinal absorption pattern, application of the biowaiver concept seems to present little risk of an inappropriate bioequivalence decision.     

Interplay of biopharmaceutics,biopharmaceutics drug disposition and salivary excretion classification systems

The aim of this commentary is to investigate the interplay of Biopharmaceutics Classification System (BCS), Biopharmaceutics Drug Disposition Classification System (BDDCS) and Salivary Excretion Classification System (SECS). BCS first classified drugs based on permeability and solubility for the purpose of predicting oral drug absorption. Then BDDCS linked permeability with hepatic metabolism and classified drugs based on metabolism and solubility for the purpose of predicting oral drug disposition. On the other hand, SECS classified drugs based on permeability and protein binding for the purpose of predicting the salivary excretion of drugs. The role of metabolism, rather than permeability, on salivary excretion is investigated and the results are not in agreement with BDDCS.

Conclusion

The proposed Salivary Excretion Classification System (SECS) can be used as a guide for drug salivary excretion based on permeability (not metabolism) and protein binding.     

A comparative analysis of biopharmaceutics classification system and biopharmaceutics drug disposition classification system: A cross-sectional survey with 500 bioequivalence studies

Although policies of waiving bioequivalence studies are part of the legal framework of various regulatory agencies, there is no harmonization with regard to extension of the biowaiver to drugs other than those with high solubility and high permeability, nor is there any consensus or official endorsement of the biopharmaceutics drug disposition classification system (BDDCS). To better understand the applicability of the biowaiver, we carried out a cross-sectional survey to estimate the relative risk of obtaining nonbioequivalent (non-BE) or bioinequivalent (BIE) results for drug products containing drugs belonging to each of the biopharmaceutics classification system (BCS) and BDDCS classes. Five hundred bioequivalence studies were randomly sampled from a database of the Brazilian Health Surveillance Agency (ANVISA). The drugs were classified according to the BCS and BDDCS, to evaluate how characteristics related to drug and dosage form influence the outcome of bioequivalence studies. The relative risk of obtaining a non-BE result was approximately four times lower for drugs in classes 1 and 3 of BCS or BDDCS when compared with class 2 drugs. Thus, it seems that the final outcome of a bioequivalence study is strongly influenced by the solubility of the drug, but not by its intestinal permeability or extent of metabolism.     

Applying the biopharmaceutics classification system to veterinary pharmaceutical products. Part I: biopharmaceutics and formulation considerations

The complexity of multiple species approvals continues throughout the life of a product as post-approval manufacturing changes, as well as all generic versions of approved products, are evaluated for each of the approved target animal species. In comparing product bioavailability across animal species, it is not unusual to observe marked interspecies differences. For many compounds, these differences reflect species-specific presystemic metabolism. However, a host of other variables must also be considered, including in vivo drug solubility, gastric transit time, intestinal permeability, diet, and species-by-formulation interactions. To predict potential species-by-formulation interactions, one must consider the solubility and intestinal permeability of the drug entity, the type of formulation, nature of the excipients, and the physiological characteristics of the animal recipient. In this paper, we examine manufacturing and formulation variables that can affect drug bioavailability, and the potential for species-specific differences in the responses to these formulations.     

Dengue vaccine: opportunities and challenges

Despite many successes in the field of vaccinology over the past century, several important scourges for which effective vaccines remain elusive continue to be threats to public health. The mosquito-borne dengue virus causes millions of infections in tropical and subtropical regions throughout the world, and is responsible for an annual mortality that measures in the thousands. The ubiquitous presence of dengue virus, and its potentially lethal complications, have made the development of an effective vaccine against the virus a priority. However, before such a vaccine can be created, the basic immunology surrounding dengue infection must be clarified. Such research is underway, including efforts focusing on the response of T-cells and the potentially central role of this response in dengue pathophysiology. 'Shaping' the T-cell response may be the key to successful dengue vaccine design.     

Rotavirus vaccines: opportunities and challenges

Each year rotavirus gastroenteritis episodes in young children cause more than 500,000 deaths and 2.4 million hospital admissions worldwide. Vaccine development became a priority when improved personal hygiene and living standards failed to significantly reduce this disease burden. Rotavirus vaccines were developed mimicking natural immunity by protecting against severe gastroenteritis in young children, which would otherwise lead to health-care attendance, hospitalization or even death. Licensed rotavirus vaccines appear safe and are well-tolerated. In high and middle-income countries they provide 80-100% protection against severe disease and 70-80% protection against rotavirus gastroenteritis of any severity, depending upon the population studied. However, rotavirus vaccines remain to be fully evaluated in low-income countries where reduced immunogenicity of oral vaccines, greater strain diversity and difficulties reaching target populations might decrease immunization program performance. Nevertheless, if these challenges are met, rotavirus vaccines should help reduce the 5% of all childhood deaths attributable to rotavirus gastroenteritis.     

Management of retinoblastoma: opportunities and challenges

Nano-delivery systems have significantly evolved over the last decade for the treatment of cancer by enabling site-specific delivery and improved bioavailability. The widely investigated nanoparticle systems are biodegradable polyesters, dendrimers, liposomes, mesoporous silica and gold nanoparticles. These particles when conjugated with different targeting motifs enhance the therapeutic efficiency of the drug molecules and biocompatibility. However, the application of such systems towards the treatment of retinoblastoma (RB), a rapidly spreading childhood eye cancer, still remains in its infancy. Nanoparticle-based systems that have been investigated for RB therapy have displayed improved drug delivery to the most restricted posterior segment of the eyes and have increased intra-vitreal half-life of the chemotherapy agents highlighting its potential in treatment of this form of cancer. This review focuses on the challenges involved in the treatment of RB and highlights the attempts made to develop nano-dimensional systems for the treatment of RB.     

Adaptive designs in clinical drug development: opportunities, challenges, and scope reflections following PhRMA's November 2006 workshop

This paper provides reflections on the opportunities, scope and challenges of adaptive design as discussed at PhRMA's workshop held in November 2006. We also provide a status report of workstreams within PhRMA's working group on adaptive designs, which were triggered by the November workshop. Rather than providing a comprehensive review of the presentations given, we limit ourselves to a selection of key statements. The authors reflect the position of PhRMA's working group on adaptive designs.     

Osteoporosis: challenges and new opportunities for therapy

Osteoporosis is a chronic disease that affects a large number of both men and women and is characterized by a decrease in bone mass, as well as weakened bones. It causes a significant amount of morbidity and mortality in patients and is often only diagnosed after a fracture occurs. This review will highlight recent advances in the development of novel anabolic approaches for treatment of osteoporosis, such as parathyroid hormone (PTH), calcium sensing receptor modulators, statins and prostanoid receptor agonists. Selected antiresorptive targets (cathepsin K inhibitors and vitronectin receptor antagonists) will also be surveyed.     

Treatment of postpartum psychosis: challenges and opportunities

Postpartum psychosis is a rare but serious psychiatric illness that follows delivery. Although controversy continues to surround its diagnostic status, it is generally considered an episode of bipolar disorder with accompanying psychotic features. The consequences of untreated postpartum psychosis can be serious due to the associated risk of suicide and infanticide; however, its close temporal association with childbirth should provide an opportunity to undertake prophylactic measures in women at risk for developing postpartum psychosis. This article reviews the literature concerning acute and prophylactic pharmacological treatment and suggests a comprehensive approach for management of postpartum psychosis.     

口服前药研究：机遇与挑战

前药研究是提高生物药剂学分类系统中第III和IV类药物口服吸收的有效途径之一。本文综述了近年来口服前药研究的进展，主要包括经典前药设计和靶向前药设计。经典前药设计重在改善母体药物的油水分配系数或减少药物的代谢。靶向前药设计重在主动利用胃肠道的生理特性靶向组织、酶及肠内流转运器，其中靶向小肠内流转运器-肽类转运器的口服前药成为目前研究的热点。前药研究还面临选题，设计和体内研究等方面的挑战。