Testing forced degradation

Recent publications on the topic of stress testing/forced degradation studies reveal that there is still a tremendous variability in the conditions... 

The reaction databases let scientists easily and quickly retrieve information about the chemistry of known substances, some of which might be similar to the investigational compounds under study in forced degradation testing. Many of the readers of this book will already be acquainted with these informatics resources on their desktop computers. 

Forced degradation studies are carried out either in the solution state and/or in the solid state. Usually the forced degradation testing is carried out on one batch of drug substance and/or one formulation blend (capsules and tablets). This forced degradation testing should not be part of a formal stability program. 

In a typical degradation test, a specimen from the PPE or, in some cases (e.g., a glove), the entire item is immersed in the pesticide for some period of time. At predetermined intervals, the specimen is removed, tested, and observed. In the laboratory, strength, puncture, and tear properties are commonly measured using a machine with which the specimen is stretched and the force required to stretch the specimen recorded. Significant increases or decreases (+20%) in any of the properties would be indicative of poor resistance to the pesticide formulation. Losses in these properties would generally result from the sorption of one or more components of the pesticide formulation by the glove material. 

In Situ Biological Degradation Test at Kelly Air Force Base, TX, Volume 1 Site Characterization, Lab Studies, and Treatment System Design and Installation... 

In Situ Biological Degradation Test at Kelly Air Force Base, TX,... 

For drug substances, photostability testing should consist of two parts forced degradation testing and confirmatory testing. 

Forced degradation testing studies are those undertaken to degrade the sample deliberately. These studies, which may be undertaken in the development phase normally on the drug substances, are used to evaluate the overall photosensitivity of the material for method development purposes and/or degradation pathway elucidation. 

The degradation of the composite laminates can be modelled as simple strength criteria for fibres or matrix, before delamination occurs. Eigure 9.19 shows the test force history for a 200 x 200 mm plate and the various numerical EE (77) predictions (Davies et al. [42]), The hnear elastic case does get the time of the event but underestimates the peak force by a factor of 3. The damaged EE prediction overestimates the force but does get the departure from the linear solution correctly. The fuUy degraded solution (with much fibre failure) does match the experimental history. Delamination was confined to one interface near the mid-plane as the C-scan image indicates. 

Thus, both the proper conduct of the testing programme and the valid use of the data depend on an understanding of the nature of organic coatings and of the forces through which they are degraded. 

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