Biopharmaceutical assessment

U. Gundert-Remy and H. Mufler, eds.. Oral Controlled Release Products Therapeutic and Biopharmaceutic Assessment, Wissenschafdiche VedagsgeseUschaft mbH, Stuttgart, Germany, 1990. 

For the different purposes presented here, cell culture models can provide the basis of screening, biopharmaceutical assessments, and evaluations for mechanistic purposes and some considerations for optimal and rational design are discussed below. 

The initial formulation for most drugs is to allow basic in vivo toxicology, pharmacology and biopharmaceutical assessments to be conducted. Aqueous solutions for injection are optimum for this application since the entire dose is administered at a single time point and the problem of bioavailability does not arise. It is important that these formulations are considered carefully, particularly for drugs that are poorly water soluble, because potentially useful compounds may be rejected inadvertently. These early formulations are also crucial because they set an in vivo benchmark for the drug s future performance. 

Chapter 4 describes the importance of drug delivery and biopharmaceutical factors in the candidate drug selection phase. Consideration is given to the intended route of administration and what predictions can be made and useful information gained from biopharmaceutical assessment of the candidate drug. 

Drug Studies in Pediatric Patients Medical Officer s Review Statistical Review Evaluation Chemistry, Manufacturing and Controls CDER Labeling and Nomenclature Committee Clinical Pharmacology/Biopharmaceutics Microbiologist s Review Pharmacokinetics Review Carcinogenicity Assessment... 

In other cases, the widespread application of a biopharmaceutical may be hindered by the occurrence of relatively toxic side effects (as is the case with tumour necrosis factor a (TNF-a, Chapter 9). Finally, some biomolecules have been discovered and purified because of a characteristic biological activity that, subsequently, was found not to be the molecule s primary biological activity. TNF-a again serves as an example. It was first noted because of its cytotoxic effects on some cancer cell types in vitro. Subsequently, trials assessing its therapeutic application in cancer proved disappointing due not only to its toxic side effects, but also to its moderate, at best, cytotoxic effect on many cancer cell types in vivo. TNF s major biological activity in vivo is now known to be as a regulator of the inflammatory response. 

Bioavailability and bioequivalence are also usually assessed in animals. Such studies are undertaken as part of pharmacokinetic and/or pharmacodynamic studies. Bioavailability relates to the proportion of a drug that actually reaches its site of action after administration. As most biopharmaceuticals are delivered parenterally (e.g. by injection), their bioavailability is virtually 100 per cent. On the other hand, administration of biopharmaceuticals by mouth would, in most instances, yield a bioavailability at or near 0 per cent. Bioavailability studies would be rendered more complex if, for example, a therapeutic peptide was being administered intranasally. 

Clinical trials serve to assess the safety and efficacy of any potential new therapeutic intervention in its intended target species. In our context, an intervention represents the use of a new biopharmaceutical. Examples of other interventions could be, for example, a new surgical procedure or a novel medical device. Veterinary clinical trials are based upon the same principles, but this discussion is restricted to investigations in humans. Clinical trials are also prospective rather than retrospective in nature, i.e. participants receiving the intervention are followed forward with time. 

Bioassays represent the most relevant potency-determining assay, as they directly assess the biological activity of the biopharmaceutical. Bioassay involves applying a known quantity of the substance to be assayed to a biological system that responds in some way to this applied stimulus. The response is measured quantitatively, allowing an activity value to be assigned to the substance being assayed. 

Sinko PJ, Lee YH, Makhey V, Leesman GD, Sutyak JP, Yu H, Perry B, Smith CL, Hu P, Wagner EJ, Falzone LM, Mcwhorter LT, Gilligan JP and Stern W (1999) Biopharmaceutical Approaches for Developing and Assessing Oral Peptide Delivery Strategies and Systems In Vitro Permeability and In Vivo Oral Absorption of Salmon Calcitonin (Set). Pharm Res 16 pp 527-533. 

The buccal mucosa does serve as an alternative route for administering compounds systematically however, to ensure particular compounds are candidates for delivery across this biological tissue, preclinical screening is essential. While in vivo human permeability studies are ideal, due to their costs and associated issues, it is necessary to perform such screening in vitro. Assessment of compound permeability across porcine buccal mucosa has been widely used and can provide the preclinical biopharmaceutical scientist with much information relating to permeability, routes of transport, and effects of various chemical penetration enhancers. 

The journey from end of discovery to commercialization is the development process of biopharmaceuticals. Scientists are an integral part of the company assessing the advantages and drawbacks of a candidate molecule from the discovery... 

Phase II studies encompass a detailed assessment of the compound s safety and efficacy in a larger patient population (a few-to-several hundreds of patients). It is important that any formulation selected for these studies must be based on sound biopharmaceutical and pharmaceutical technology principles. Phase III clinical studies, also referred to as pivotal studies, involve several thousands of patients in multiple clinical centers, which are often in multiple countries. The aim of these studies is to demonstrate long-term efficacy and safety of the drug. Since these studies are vital in the approval of the drug, the dosage form plays a very critical role. 

Small-scale in vitro test systems may now be employed to assess biopharmaceutical properties or the drug s potential behaviour after in vivo administration. For example, drug penetration through monolayers of epithelial cells in tissue culture can be used to examine bioavailability. The drug s metabolism can be studied in vitro using hepatic microsomes and potentially toxic metabolites identified before problems arise in vivo Although not absolute, these tests... 

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