Early phase methods stability

An additional key validation criterion for early phase methods is an evaluation of solution stability to establish that the API and related substances do not degrade in the solvent system used for sample preparation. This allows for limits to be set for solution lifetime. 

Unlike early-phase methods, the criteria for late-phase release and stability studies are well defined by regulatory guidelines (see Chapter 12). Although it has been emphasized earlier that discussion of validation issues will not be a primary focus of this chapter, method development must be performed in the context of meeting regulatory expectations. Minimal discussion of regulatory considerations will, therefore, be interjected, where applicable, to the discussion of method development. 

All phases of analytical development are ideally supported by chemical separation techniques such as HPLC, TLC, GC, SFC, and CE. HPLC continues to be the primary method of analysis throughout the pharmaceutical development process. Although HPLC is limited in its ability to separate more than 15-20 components in a single analysis, and variations in columns and instrumentation manufacturer to manufacturer complicate transfer of methods, HPLC can readily be implemented to meet ICH requirements for method performance. For early-phase methods, HPLC can be coupled dynamically to mass and nuclear magnetic resonance spectrometers to facilitate the identification of unknown impurities. In later phases, HPLC can be implemented in a fully automated format as a high-throughput method for release and stability testing. 

CE methods are developed and utilized in pharmaceutical QC for early to late phases of drug development. Chapter 4 covers the approaches for late-phase development for small molecules that can be used in early-phase development, as well as for large-molecular-weight compounds. Late-phase method development in pharmaceutical QC is performed for required stability studies and for release of the drug product or drug substance validation batches, and is intended to be transferred to the operational QC laboratories for release testing of the production batches. Preferably, late-phase methods should be fast, robust, reliable, and transferable. Therefore it is crucial to devote adequate time, thought, and resources to the development of such methods. 

Whereas the other separation methods have been demonstrated to also provide the requisite performance for release and stability testing for select drug substances and drug products, more typically the techniques are applied as supportive methods for HPLC during early-phase development and in niche areas during late-phase development. Because each separation method provides a different mechanism of separation to HPLC, utilization in early-phase development can be used to confirm specificity of HPLC methods. In later phases, both SFC and CE have shown applicability to chiral separations, and GC remains as the unique technique for the determination of residual solvents. 

In the United States, the concept of aerobic bioreactor landfill where the wastes are subjected to the active aeration from the early phase of landfill lifetime, was developed. Additionally, in order to accelerate the waste stabilization, the leachate recirculation is used. In Asia, the other solution for the reduction of methane production inside the landfill was elaborated. It consists in landfill self-aeration caused by the differences in inner and outer landfill temperatures (Fukuoka method). 

Synthetic peptides have been extensively used to study the thermal stability and folding of the triple helix. These peptides can be synthesized as either single chains or cross-linked peptides. Early on, such peptides were synthesized by polycondensation of tri- or hexapeptides, which led to a broad mass distribution that was difficult to separate. With the advances of solid-phase synthesis methods, peptides with defined chain length became available. The most studied collagen-like peptides are (Gly-Pro-Pro) or (Pro-Pro-Gly) and (Gly-Pro-4(if)Hyp) or (Pro-4(if)Hyp-Gly) with n varying from 5 to 15. Sutoh and Noda" " introduced the concept... 

The early work of Schwarz and Johnson (1983) used a prediction of the underlying thermodynamics of the Au-La system to explain the relative stability of the liquid/amorphous phase in their elemental layered composites (Fig. 11.7). However, they utilised the method proposed by Miedema (1976) for thermodynamic stability of the liquid/amorphous phase. There are clear limitations to the Miedema approach firstly it is not guaranteed to produce the correct phase diagram and therefore phase competition is at best only approximated, and secondly, the thermodynamics of the terminal solid solutions are chosen quite arbitrarily. 

In the early 1970s Li [13] proposed a method that is now called Emulsion (surfactant) Liquid Membrane (ELM) or Double Emulsion Membrane (DEM) (Fig. 3). The name reveals that the three liquid system is stabilized by an emulsifier, the amount of which reaches as much as 5 % or more with respect to the membrane liquid. The receiving phase R, which usually has a smaller volume than the donor solution, F of similar nature, is finally dispersed in the intermediate phase, M. In the next step the donor solution F is contacted with the emulsion. For this purpose, the emulsion is dispersed in the donor solution F by gentle mixing typically in a mixer-settler device. After this step, the emulsion is separated and broken. The enriched acceptor solution is further processed and the membrane liquid M is fed back for reuse. 

Such was the state of the art when Amundson and Bilous s paper was published in the first volume of the newly founded A.I.CH.E. Journal (Bilous and Amundson, 1955). This for the first time treated the reactor as a dynamical system and, using Lyapounov s method of linearization, gave a pair of algebraic conditions for local stability. One of these corresponded to the slope condition of previous analyses, and there was a brief flurry of attempts to invest the other with a similarly physical explanation. For the global picture they introduced the phase plane (another feature of the theory of dynamical systems) and, with consummate skill, Bilous conjured the now classic figures from a Reeves electronic analogue computer. Even in this early paper, they had touched upon the consecutive reaction scheme A - B - C and had shown that up to five steady states might be expected under some conditions. 

Rancidity measurements are taken by determining the concentration of either the intermediate compounds, or the more stable end products. Peroxide values (PV), thiobarbituric acid (TBA) test, fatty acid analysis, GC volatile analysis, active oxygen method (AOM), and sensory analysis are just some of the methods currently used for this purpose. Peroxide values and TBA tests are two very common rancidity tests however, the actual point of rancidity is discretionary. Determinations based on intermediate compounds (PV) are limited because the same value can represent two different points on the rancidity curve, thus making interpretations difficult. For example, a low PV can represent a sample just starting to become rancid, as well as a sample that has developed an extreme rancid characteristic. The TBA test has similar limitations, in that TBA values are typically quadratic with increasing oxidation. Due to the stability of some of the end-products, headspace GC is a fast and reliable method for oxidation measurement. Headspace techniques include static, dynamic and solid-phase microextraction (SPME) methods. Hexanal, which is the end-product formed from the oxidation of Q-6 unsaturated fatty acids (linoleate), is often found to be a major compound in the volatile profile of food products, and is often chosen as an indicator of oxidation in meals, especially during the early oxidative changes (Shahidi, 1994). 

---