Impurity clearance

Contaminant/Impurity Clearance. Classes of contaminant removal include process-related, host-cell related, andproduct-related (e.g., aggregates,deaminations, and oxidations) substances [14]. Contaminant clearance studies can be used to avoid lot-to-lot acceptance criteria because safety margins of several logs of excess clearance are demonstrated [33]. In these studies, a contaminant is added to the input feed stream at the small scale, its recovery is measured at each stage of the... 

At the preclinical product phase, critical and noncritical classification of process input parameters should be initiated [32]. Critical components of facility subsystem validation need to be essentially complete before phase I product manufacture [15]. For phase I, it is necessary to validate aspects of the process related to product safety (e.g., sterility, mycoplasma, viral clearance, impurity removal, and stability) [14]. Abbreviated viral clearance studies for model viruses/retroviruses and impurity clearance studies for host cell DNA often are acceptable, resulting in fewer downstream steps validated at this product stage [3, 5]. If viral clearance results are available in sufficient time, the results can be applied to developing the phase I process steps. All assays do not have to be validated at this stage, but some (especially product-specific ones) should be at least qualified [14]. 

Feed/centrate flowrate Impurity clearance (host... 

The small cartridge units can be conveniently placed ahead of instruments, close-clearanced pumps, or a process to remove last indications of impurities in suspension. 

Traditionally, HPLC, GC-MS, or LC-MS methods were used to monitor the clearance of small-molecule impurities. These analytical techniques often require unique solvents, columns, methods, reagents, detectors, and buffers for each analyte to be quantified. The NMR method, albeit not the most sensitive technique, normally does not have these problems. In this chapter, some examples will be used to demonstrate that NMR is a fast, generic, and reliable analytical technique for solving analytical problems encountered in the development of biopharmaceutical products. The NMR techniques described here require minimal sample handling and use simple standard NMR methods. They can easily be implemented and used for process development and validation purposes. 

Figure 12.1 Clearance of small-molecule impurities from process buffers in a formulated protein product. Trace A the NMR spectrum of a control sample containing a mixture of three components (succinate, tetraethylammonium, and tetramethylammonium) in the final formulation buffer (sodium acetate). These three components were used in the recovery process for a biopharmaceutical product. Traces B and D the proton NMR spectra of the formulated protein product. No TEA or TMA were detected, but a small amount of succinate was observed in this sample. Traces C and E the proton NMR spectra of a formulated protein product spiked with 10 jag/ml of succinate, TEA, and TMA. Traces D and E were recorded with CPMG spin-echo method to reduce the protein signals. The reduction of NMR signals from the protein allows for better observation of the small-molecule signals.

Figure 12.6 Two sections of the proton NMR spectrum for a protein product after the protein has been removed. Only the formulation buffer (25 mM citrate) and a small amount ( 1 pg/ml) of residual Tris (a component of the penultimate buffer used in the recovery process prior to the final UF/DF formulation step) are observed after the filtration. The signal-to-noise ratio of Tris is about 70. The absence of any other significant proton NMR signals provides compelling evidence for good clearance of any other small proton-containing molecule impurities.

We may regard the commercial polymers which have broad technical application separately. The photosensitivity of such materials, as a rule, is caused by impurities and dopants. The main reason for studying their photoelectrical processes is the clearance of the stabilization problems. 

In the early days of biotechnology product development, the focus was on quality issues [4] or process-related impurities.The concerns at that time were for carryover of other cellular proteins and DNA and for contamination with endotoxins, chemicals, and viruses. Of course, these concerns still exist, but methods for purification and assays for evaluation of clearance have alleviated the need for the safety assessment scientist to focus on contaminants instead they are now asked to focus on the pharmacological activity of the molecules. An ICH guidance (Q6B Specifications Test Procedures and Acceptance Criteria for Biotechnological/Biological Products) addresses the specific issues related to the manufacturing process [6], Other product-related issues such as impurities do need to be considered by the safety assessment scientist, for... 

The principle is to have about three steps the first with specific properties to capture the antibody from the crude feedstock, the second to separate impurities, and the third to play a polishing role with properties to remove traces of peculiar agents such as nucleic acids and endotoxins, and able to add virus clearance. 

Increasing solubility because of increased concentration of impurities will result in a similar equilibrium change, although in some cases, the effect could be much greater. In extreme cases, when the residual solvent concentration is reduced to less than a critical value, the substrate could melt or solidify, depending on the melting point and the impurity effect. This condition is often used in laboratory preparations for convenience in changing solvents and is referred to as concentration to dryness. It is obviously not a scalable operation in a stirred vessel. Specialized tubular evaporators with close-clearance or scraped-surface rotors are available for these applications and have been successfully used by the authors for concentration but not for simultaneous crystallization. 

Free Tc-pertechnetate adds to increased background activity. Reduced, hydrolized Tc activity is bound to plasma proteins in circulating blood, interfering with the measurement of plasma clearance (Rehling 1988). Therefore, quality control of Tc-DTPA chelate should be performed before administration to patients. When Tc-DTPA is used to measure GFR, it is necessary to remove the protein-bound impurity by passing the plasma through an ultrafilter before the measurement of radioactivity (Rowell et al. 1986). 

The limit of quantitation (LOQ) is the lowest concentration that produces a signal 10-fold above background, whereas the limit of detection (LOD) is the lowest concentration that produces a signal threefold above background [75]. The assay sensitivity and achievable concentration limits of additives define a window of clearance, which is the difference (on a log scale) between the highest attainable initial contaminant/impurity concentration and the lowest detectable concentration (LOD) of that additive [12]. This difference is the amount that can be measured and thus the amount that can be claimed to have been removed by the process [12]. 

Scale-down studies have been used for a wide variety of process validation studies, including resin lifetimes, in-process stream hold times, buffer stability, virus clearance, harvest criteria, filter extractables, resin leachables, and cell age at harvest [14, 91, 92]. The ease of scale-down differs depending on step and should be considered in selecting those steps to be validated [5]. In fact, certain validation issues can be addressed only via small-scale models (e.g., virus clearance evaluation, nucleic acid and other impurities/additives removal, cleaning and storage procedure evaluation, and column lifetime estimation) because their use increases worker safety, reduces costs, and permits use of higher titer samples for improved... 

The attachment of PEG to bioactive macromolecules is called PEGylation and provides various benefits [312]. These include better water solubility, enhanced resistance to proteolysis, decrease of immimogenicity, antigenicity, toxicity of drugs and slower rate of kidney clearance [313]. PEG has been approved for use in drugs, food and cosmetics [314]. The monodispersity of todays available PEGs eliminates former risks that were related to impurities foimd during chemical synthesis of PEG. 

A good seal should have many properties. Firstly, it must not degrade, or lose its elastieity in contact with the fluids being handled, even at extremes of temperature and pressure. It must not become permeable to these fluids, react with them or contaminate them with impurities. The seal must not swell appreeiably when in contact fluids, even at elevated temperatures. For example, if an O ring in eontaet with a moving surface swells appreciably, it may be extruded into a close-clearance area where it will be tom by friction. When the pressure or temperature is then reduced, the O ring may shrink from its extmded position in a way that causes fluid leakage. 

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