Excipients biological products

Regulatory agencies currently set stringent standards on the quantities of nucleic acids allowed in recombinant biological products. In the pharmaceutical industry these requirements necessitate the quantification of trace amounts of nucleic acids in the presence of large quantities of protein and other excipients. Flourescence methods offer advantages for such analyses, but also have limitations. The use of a variety of fluorescent dyes and techniques is described here, and practical examples of such use are presented. 

Pharmaceutical Excipients Characterization by IR, Raman, and NMR Spectroscopy, David E. Bugay and 14/ Paul Findlay Polymorphism in Pharmaceutical Solids, edited by Harry G. Brittain Freeze-Drying/Lyophilization of Pharmaceutical and Biological Products, edited by Louis Rey and Joan C. May... 

For biological products (the chemical) excipients are often overlooked. They, too, may have effects or side effects and can leave residues in animals that end up in human food. Their choice for a development product must be considered carefully. Either one uses ingredients with a well established quality and safety profile or one must face the fact that a variety of analytical and safety data have to be established for these excipients. Safety studies for new excipients may cost more than the safety assessment of the biological product itself. 

User safety-related investigations are unlikely for most biological products. However, some excipients and special vaccines (e.g. poultry live vaccines for spray applications) may warrant studies addressing the user safety during application. 

Appendices This section is most likely to contain additional data associated with biological-based products. It should contain information as regards the facilities and equipment used for the manufacture of biotech products. Assessment of the risk of contamination from adventitious agents such as transmissible spongiform encephalopathy agents (TSEs), bacteria, mycoplasma, fungi or viruses should also be provided. Additional information on novel excipients that have not been used before should also be included in this section. 

The decision to market the product in liquid or powder form is often dictated by how stable the protein is in solution. This, in turn, must be determined experimentally, as there is no way to predict the outcome for any particular protein. Some proteins may remain stable for months (or even years) in solution, particularly if stabilizing excipients are added and the solution is refrigerated. Other proteins, particularly when purified, may retain biological activity for only a matter of hours or days when in aqueous solution. 

Table 6.7 Some major excipient groups that may be added to protein-based biopharmaceuticals in order to stabilize the biological activity of the finished product...

A variety of analytical methods, such as ELISA and HPLC, can be used to evaluate the effect of excipients or lyophilization on the stability of the biophar-maceutical product. Some parameters the analytical methods should evaluate are degradation, chemical and physical changes, aggregation, adsorption, and loss of biological activity. 

The study of reaction rates or kinetics of a particular denaturation process of a protein therapeutic can provide valuable information about the mechanism, i.e., the sequence of steps that occur in the transformation of the protein to chemically or conformationally denatured products. The kinetics tell something about the manner in which the rate is influenced by such factors as concentration, temperature, excipients, and the nature of the solvent as it pertains to properties of protein stability. The principal application of this information in the biopharmaceutical setting is to predict how long a given biologic will remain adequately stable. 

The tests for microbial limits and recommendations for microbial quality criteria of raw materials, excipients, drug substances, and pharmaceutical products have been established in pharmacopoeial compendia for over 30 years. These tests are listed in the USP 24 Chapter (61) Microbial Limits Tests and in the Ph. Eur. 3rd ed.. Biological Tests 2.6.12 and 2.6.13, Microbial Contamination of Products Not Required to Comply with the Test for Sterility (total viable count, tests for specified microorganisms) and the JP XIII 30 Microbial Limit Test. 

Drug products contain both drug substance (sometimes referred to as the Active Pharmaceutical Ingredient [API]) and excipients. The resultant biological, chemical and physical properties of the dmg product are directly dependent on the excipients chosen, their concentration and interactions with the API [1]. 

Preformulation testing provides a basic dossier on the compound and plays a significant role in identifying possible problems and suitable approaches to formulation. Such dossiers already exist for the common excipients. The requirement for aqueous solubility is paramount and preformulation can identify salt forms that are appropriate for further development. Stability and solubility studies wiU indicate the feasibility of various types of formulation such as parenteral liquids and their probable shelf lives. Similar information can be garnered for solid products from the solid physical properties. By performing these studies on a series of candidate compounds, the optimum compound can be identified and further biological and chemical studies guided to provide the best results. 

Filgrastim is a recombinant human G-CSF (produced in E. coli), approved for chemotherapy-induced neutropenia since 1991. Although the 18.8 kDa recombinant product is not glycosylated and contains an additional N-terminal methionine residue (due to expression in E. coli), it displays biological activity indistinguishable from native G-CSF. The product is presented in freeze-dried format and contains buffer elements as well as sorbitol and Tween as excipients. 

Intimately related to these factors is the design of the device, formulation, and the interface with the patient. Much of the discussion below will focus on the implications of excipients on formulation challenges for inhaled aerosol products. This chapter summarizes excipients for pulmonary formulations from several perspectives (i) excipient selection based on principles of delivery, (ii) physicochemical requirements for excipients, and (iii) specific challenges for formulations faced with aerosol drug delivery systems, including (a) biological aspects, (b) microbiological aspects, (c) analytical issues, and (d) future prospects. 

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