A Forced Degradation Study (Stress Testing)

The stability of a drug product or a drug substance is a critical parameter that may affect purity, potency, and safety. Changes in drug stability can risk patient safety by the formation of a toxic degradation product(s) or deliver a lower dose than expected. Therefore it is essential to know the purity profile and behavior of a drug substance under various environmental conditions.

Chemical stability is one of the most important issues that impact the quality and safety of pharmaceuticals. The FDA and ICH require stability testing data to understand how the quality of an API or a drug product changes with time under the influence of environmental factors such as heat, light, and humidity. Knowledge of these stability characteristics defines storage conditions and shelf life, the selection of proper formulations and protective packaging, and is required for regulatory documentation.

Various analytical techniques/equipment can be used to separate and estimate all the degradant compounds expected to be present at the time of the forced degradation study. HPLC with UV detector (HPLC-UV) and photodiode array detector (HPLC-PDA) are well-known techniques and are widely used in pharmaceutical industries during forced degradation studies as part of the development and validation of the stability-indicating method. HPLC with mass detector (LC-MS), gas chromatography with mass detector (GC-MS), and nuclear magnetic resonance (NMR) spectroscopy are important techniques to identify the structure of the degradants.

What is Forced degradation study?

• Forced degradation studies typically involve the exposure of a representative sample of a drug substance or drug product to the relevant stress condition of light, heat, humidity, acid/base hydrolysis and oxidation. 
• Forced degradation plays an important role in the drug development process. It furthers understanding of the chemistry of the drug substance and drug product and facilitates the development of stability indicating analytical methodology.

Important Applications of The Forced Degradation Study

Forced degradation is a critical analytical study for the development of stability-indicating methods to be used by pharmaceutical companies as part of regulatory submissions to the FDA. Some of the applications of the studies are:

• To develop and validate stability-indicating methods as per ICH guidelines.
• To identify structure and toxicity and to set up specifications of degradants or impurities.
• To propose the shelf life of the product without real-time stability information.
• To optimize formulations and to select placebos for drug products to avoid interference.
• To justify impurities that are process-related or degradation products.
• To support identification of root cause during out-of-specification (OOS)/lab investigations.
• To accompany drug master file and ANDA/NDA and IND submissions to the FDA.

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Forced degradation studies are carried out for the following reasons:

• To develop and validate a stability-indicating method
• To determine degradation pathways of drug substances and drug products (e.g., during the development phase)
• To identify impurities related to drug substances or excipients
• To understand the drug molecule chemistry
• To generate more stable formulations
• To generate a degradation profile that mimics what would be observed in a formal stability study under ICH conditions
• To solve stability-related problems (e.g., mass balance).

Testing of stress samples is required to demonstrate the following abilities.

• To evaluate the stability of drug substances and drug products in solution.
• To determine structural transformations of drug substance and drug product.
• To detect low concentrations of potential degradation products.
• To detect unrelated impurities in the presence of the desired product or product-related degradants.
• To separate the product-related degradants from those derived from excipients and intact placebo.
• To elucidate possible degradation pathways.
• To identify degradation products that may be spontaneously generated during storage and use.

Forced degradation studies are designed to generate product-related variants and develop analytical methods to determine the degradation products formed during accelerated and long-term studies.

The degradation products observed in such studies are "potential" degradation products that may or may not be formed under relevant storage conditions, but these products reveal the degradation pathways available to the drug and facilitate the development of stability-indicating analytical methods.

Any significant degradation product should be evaluated for potential hazard and the need for characterization and quantitation.

Forced degradation or stress studies of drug substances are usually conducted in solution and the solid state at temperatures exceeding accelerated stability conditions (>40°C). The degradation pathways investigated include hydrolysis, oxidation, thermolysis, photolysis, and polymerization. Hydrolysis is investigated in solution over a broad pH range and in the solid state by exposure of the drug to high relative humidity.

Oxidation in the solution can be investigated through control of exposure to molecular oxygen or by the addition of oxidizing agents such as peroxides. The effects of thermolysis are usually assessed in the solid state by applying heat. Photolysis is investigated in solution or the solid state by irradiating samples with light with wavelengths in the 300-800 nm range; photooxidation can be investigated with light under an oxygen atmosphere. 

Drug substance polymerization can be investigated by measuring the rate of degradation as a function of different initial drug substance concentrations in solution and LC/MS analysis of degradation products. /script>

Extend of degradation

A degradation level of 10-15% is considered adequate for the validation of a chromatographic purity assay.

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Regulatory and Scientific Guidance by Phase

Although forced degradation studies are a regulatory requirement and scientific necessity during development, they are not considered part of the formal stability program. The guidance gives recommendations for conducting studies at the various phases of development.

Selection And Procedures Of Forced Degradation Condition

• As per ICH guidelines and common industry practice, forced degradation is usually performed in different stress conditions, i.e., acid, alkali, peroxide, thermal, and UV, along with a control sample. There are no industrial guidelines about how much degradation should be achieved; however, per current industrial practices, 5 to 30 percent degradation should be achieved in any one of the applied stress conditions.  
• The aim of the degradation to be achieved through stress testing is to mimic the control room temperature stability conditions. In cases where higher or lower degradations are observed, the conditions or concentrations of the reagent should be optimized. Mass balance should be demonstrated during the degradation study and it should be around 100%, taking into consideration margins of analytical errors. All the degradants/impurities must be calculated during mass balance evaluations.

During the forced degradation study, any batch that will not be the part of regulatory submission can be used. In the case of a drug product, if multiple strengths are available with the same placebos and different amounts, the strength that has the highest ratio of placebo vs. active pharmaceutical ingredient (API) should be used. Where placebos are different, then forced degradation of all the strengths must be demonstrated. During the drug product degradation study, both the placebo and API must be demonstrated to identify actual degradation pathways. Where placebos are different for different strengths of drug products, then all the placebos should be considered for the degradation study.

The following Table suggested degradation conditions as per current industrial practices and accepted by the FDA during DMF/ANDA/NDA and IND submissions for regulatory approval.

• Degradation should be performed in solid or solution form, but it is recommended it be performed in solution form using the diluent/mobile phase to obtain a homogeneous effect. Degradation studies can be initiated with harsh conditions (i.e., high concentration of reagent with high temperature) to shorten the time of the study. In cases where degradation of more than 30 percent is found, milder conditions should be applied by reducing the concentration of the reagent, lowering the temperature, etc. 
• Degradation conditions shall be optimized to achieve a target based on the initial degradation outcome. pH should be adjusted to about 7.0 for acid and alkali degradation to extend the shelf life of the chromatographic column. If degradation is not found in any of the above conditions, different reagents and conditions can be applied, e.g., H2SO4, Zn, etc. There are a few molecules that do not degrade under any harsh conditions and they are therefore considered rock-stable molecules. This kind of molecule will not generate any additional impurities/degradant peaks during a stability study.

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