Factors affecting stability testing of drugs and degradation study guidelines

Jonah Panting

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Technical Review Article | Open Access | Published 29th September 2026

Factors affecting stability testing of drugs and degradation study guidelines

Sandip Bodkhe, Pankaj Bhamare^*Amity Institute of Pharmacy, Amity University Maharashtra, India.

| EJPPS | 313 (2026)| https://doi.org/10.37521/ejpps31309

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Abstract

Stability testing is critical for ensuring that pharmaceutical products remain safe, potent, and effective throughout their shelf life. Drug degradation can occur due to various intrinsic (chemical structure) and extrinsic (temperature, humidity, light, pH) factors. This review examines the principal factors affecting drug stability, regulatory guidelines from the International Council for Harmonisation (ICH), Brazilian National Health Surveillance Agency (ANVISA), and China, as well as forced degradation methodologies. Accelerated stability testing provides rapid prediction of product shelf life under stress conditions, while real-time studies ensure long-term safety. Recent product recalls illustrate the critical importance of comprehensive stability assessment and root cause analysis. We synthesize current knowledge on stability-indicating analytical methods, regulatory compliance strategies, and emerging practices to support pharmaceutical development and quality assurance. This review encompasses intrinsic factors (chemical structure, polymorphism), environmental factors (temperature, humidity, light, pH), excipient interactions, accelerated and forced degradation protocols, and practical case studies demonstrating real-world applications.

Keywords: Stability Testing, Drug Shelf Life, ICH Guidelines, ANVISA Guidelines, Accelerated

Stability, Forced Degradation.

Introduction

Stability testing is a very important factor as it indicates how safe and effective the medicine is for the patient to consume¹. According to the US food and drug administration (USFDA), the expiration date which is printed on a label shows the time duration for which a drug is expected to be safe and potent if stored under recommended conditions ². However some studies such as the shelf life extension programme (SLEP) of the FDA can show that some drugs will remain stable, effective and safe after the expiration period. These drugs remain stable for several years beyond the declared shelf life, which will reduce unnecessary waste and protection to the environment to some extent ³. Stability testing involves testing different physical properties of a drug for a long period. This includes physical changes such as change in colour, change in appearance, chemical changes such as breakdown of active ingredients, development of unspecified degradation products (impurities), spillage of drug, microbial contamination and therapeutic properties which relate to how well the drug works ². The study must be conducted under defined conditions with controls on light, humidity and temperature^¹.

Overall this review highlights that proper and updated stability testing is important to avoid wastage, avoid product recall, ensure long shelf life and make sure that patient will receive safe and effective medicine.

Factors Affecting Drug Stability

Stability of a drug depends on internal and external factors which breakdown effectiveness over a period. These include intrinsic factors (also known as internal factors) such as chemical structure of the drug and external factors (environmental factors) where the drug is stored, such as temperature, humidity, and light.

Temperature

Temperature is the most crucial factor which affects the drug stability, as it impacts directly the rate of chemical and physical reaction^⁴.

Temperature effect and mechanism

Higher temperature increases molecular movement and kinetic energy of drug molecules, increases probability of collision between reactant molecules and promotes breakdown of bond and rearrangement. For each 10ºC temperature rise the degradation rate increases 1.5 to 2.5%, depending upon specific chemical structure and activation energy of the reaction^⁴.

Thermal pathways of degradation

Induced temperature degradation may occur by multiple mechanisms^⁶

1) Thermal breakdown of chemical bond.

2) Hydrolysis of susceptible functional groups.

3) Acceleration of oxidative degradation.

4) Promoting isomerisation and rearrangement reaction.

5) Enhanced reaction between drug and excipient components.

Humidity

The amount of moisture in the atmosphere has a major effect on stability of many pharmaceutical products^⁴. Exposure to moisture causes a hydrolysis reaction, where there is loss of water molecules, this leads to loss of drug effectiveness. Moisture also affects the physical properties of drugs, which may change disintegration time in the body. Too much moisture can make tablets soft, sticky or cause them to crumble.

Drugs which are sensitive to humidity needs to be stored and packed in proper containers. Packing material such as the blister pack with aluminium foil, bottles with tight caps or using desiccants ⁴. (small pack of silica) are common ways to protect medicines from moisture. This will help to keep the drug stable during storage and transportation.

In accelerated stability testing drugs are often placed in a controlled environment with high relative humidity such as 75% RH (Relative Humidity). Drug behaviour is monitored on this criterion. Guidelines such as Q1A provide details of humidity test conduction to maintain drug safety and efficacy ⁶.

Effect of moisture on physical stability: ⁴

Moisture causes crystallisation from amorphous solid.
Drug may be dissolved after absorption of moisture.
Caking and powders or granules may be hardened.
Dissolution rate loss and which directly impact bioavailability.
In case of suspension there is phase separation.
Swelling and softening of tablets and capsules.

Light Exposure:

There may be photodegradation and breakdown of the drug if it comes in contact with ultraviolet (UV) and visible light. Some medicines contain compounds that are sensitive to light and must be protected. Change in chemical structure may occur when there is absorption of light, leading to formation of harmful by-products.

Drugs that are sensitive to light are protected by packing material that blocks or reduces light exposure. This includes dark coloured bottles, opaque containers that block UV rays. In stability testing drugs are exposed to a strong light source in a controlled way to simulate the effect of light over time. ICH has given guidelines for photostability studies in ICH Q1B ⁷.

pH Testing:

pH measurement is an important step to measure how acidity and alkalinity of drug formulations changes over time. Change in pH indicates chemical degradation or interactions that may affect drug safety and effectiveness. If pH varies from the optimal range, the drug breaks down faster and loses its intended effect.

Under controlled temperature and humidity, pH of liquid formulations (solutions, suspensions and injectables) ⁸ is checked at different time points. This helps to understand how stable the formulation is and whether the pH remains within the safe range throughout the shelf life.

ICH guidelines Q1A(R2) provides stability testing procedure for pH measurement ⁶. Maintaining pH during stability studies helps pharma companies to design better formulation. It also supports regulatory approvals proving a drug remains safe, effective and high quality until expiration.

Excipient Interactions:

Excipients are inactive ingredients added to formulations to give them the right form, taste and stability. Although they do not have any therapeutic properties, sometimes they interact with active pharmaceutical ingredients (API) or with each other. For example, some preservatives or fillers may increase the breakdown of active ingredients.

In some cases, excipients can cause physical changes such as decolouration, clumping or crystal formation in medicines ⁹. Also, quality of excipients plays an important role, as substandard quality sometimes leads to product recall. During product development excipient compatibility is monitored to check the effect on the drug and with each other. This will help to identify potential problems and ensure the final product remains stable, safe and effective throughout the shelf life ⁹.

Physical Factors:

Physical changes have impact on stability and efficacy of medicine. It includes polymorphic transitions, crystallization, and change in particle size or shape. This impacts drug solubility and bioavailability ¹⁰.

Polymorphic Transitions:

Polymorphism is the phenomenon where a drug exists in different crystal forms. These forms have varied solubility and stability. One polymorphic form may dissolve quickly while others are easily absorbed. A drug can change from one form to another form which affects performance and shelf life ¹⁰.

Crystallization:

Crystallization happens when one of the ingredients forms solid crystals from solution or suspension ¹⁰. It will change the texture or appearance of the medicine and reduces its ability to dissolve properly. It also causes loss of drug potency.

Particle Size Changes:

Particle size and shape affect how quickly a drug is dissolved in the body ¹⁰. Particles which are smaller in size are absorbed immediately and dissolved quickly. Particles may form clumps (Agglomeration) or break into pieces which changes efficacy of drug.

Some techniques are listed below for the detection and monitorization of physical changes.

There are different techniques available to detect and monitor physical changes:

X-ray Diffraction (XRD): This method helps identify the crystal structure of the drug and detects any polymorphic changes. X-rays bounce off crystals for measurement.
Microscopy: Using microscopes, researchers can observe the size, shape, and surface characteristics of drug particles. Techniques include optical microscopy and scanning electron microscopy (SEM).
Differential Scanning Calorimetry (DSC): Changing the temperature will allow monitoring of how the drug behaves and helps to identify polymorphic forms, or by observing melting point it detects crystallization and heat flow.
Particle Size Analysis: Methods such as laser diffraction or dynamic light scattering measure the size distribution of drug particles to monitor any changes over time.

By monitoring these physical properties stability testing make sure that the drug dissolves completely and emphasises the therapeutic action throughout product life cycle. Control over these physical changes maintains product consistency, safety and patient trust ¹⁰.

Stability Testing Guidelines:

Across the world there are different regulatory agencies which give certain guidelines to test medicines in a consistent and reliable way. It includes the way to perform the test and also includes conditions under which the drug should be tested, the duration of the test and the criteria for which the drug is considered as safe and potent throughout the shelf life.

These guidelines are structured in such a way that it will meet international standards.

ICH Guidelines

The International Council for Harmonization (ICH) provides the most widely accepted set of rules for stability testing of drugs. The main guideline is ICH Q1A(R2) Stability Testing of New Drug Substances and Products (2003) ⁶. This explains important aspects of stability testing, including:

Testing Conditions: Drugs must be tested under various storage conditions that simulate different climates around the world. These include long-term testing, accelerated testing, and intermediate testing. The climate zones range from Zone I (cold) to Zone IV (hot and humid). Table 1 gives detailed information about different zones along with conditions.

Table-I: ICH stability zones and Climatic conditions

STABILITY ZONES	CLIMATIC CONDITION FOR THE ZONE	COUNTRIES	TEMPERATURE & HUMIDITY FOR LONG TERM STABILITY
I	Temperate	Canada, US and Europe	21 ± 2°C temp. and 45±5% RH
II	Subtropical	Japan and southern Europe	25 ± 2°C temp. and 60 ± 5% RH
III	Hot & Dry	India, Iraq and Saudi Arabia	30 ± 2°C temp. and 35 ± 5% RH
IV a	Hot Humid & Tropical	Iran, Egypt	30 ± 2°C temp. and 65 ± 5% RH
IV b	Hot & Very Humid	Brazil, Singapore	30±2°C temp. and 75±5% RH

RH = Relative humidity

Testing Duration: Long-term stability testing usually lasts up to 12 months, while intermediate and accelerated testing is done over about 6 months. These time periods help predict how the drug will behave over its full shelf life (Table 2)

Table-II: Stability testing duration

Study	Storage condition	Minimum time period required for data submission
Long term testing	25°C ± 2°C/60% RH ± 5% RH or 30°C ± 2°C/65% RH ± 5% RH	12 M
Intermediate testing	30°C ± 2°C/65% RH ± 5% RH	6 M
Accelerated testing	40°C ± 2°C/75% RH + 5% RH	6 M

M = Month

After conducting long term stability studies at 25°C ± 2°C/60% RH ± 5% RH, if a significant change occurs during a 6 months period at accelerated storage conditions, additional testing is conducted and evaluated against significant change criteria.

In general, significant change is defined for a drug product as:

If there is change in assay value by 5% from initial value or acceptance criteria fail to meet potency when using biological and immunological procedures.
In the stability indicating method if any degradation product does not meet the shelf life specification criteria.
Acceptance criteria for appearance, physical attributes and functionality test (e.g) change in colour, phase separation, resuspendibility, cake formation, hardness, change in dose delivery per actuation). Some changes in physical attributes (e.g softening of suppositories, melting of creams) are expected under accelerated conditions.
Failure to meet the acceptance criterion for pH; or
Failure to meet the acceptance criteria for dissolution for 12 dosage units ⁶.

Accelerated stability testing:

Accelerated stability testing predicts quickly how long a drug will remain stable and effective. Instead of conducting real time data for several years, here the drug is exposed to harsh conditions such as temperature, humidity and light ¹³. These conditions lead to drug degradation and allow drug developers to observe changes within a short period of time.

According to ICH Q1A(R2) guidelines accelerated testing is usually conducted at 40°C ± 2°C and 75% ± 5% relative humidity for about six months.

Advantages of stability testing:

Saves Time and Costs
Compared to a real-time stability study, accelerated testing allows drug developers to predict drug stability within a shorter period of time, which ultimately reduces both time and money for stability assessment.
Early Detection of Problems
Early in the development process, it helps to identify formation of possible degradation products. This helps to improve formulations and avoid future stability issues.
Supports Provisional Shelf Life
A temporary shelf life of a drug can be assigned which allows it to be marketed whilst a long-term study is proceeding. This will allow the medicine to be available sooner.

Limitations:

Non-Proportional Degradation
All the degradation reactions will not speed up proportionally under the stress conditions, such as heat or humidity. This means accelerated testing may not always predict accurately the behaviour of a drug under normal storage condition.
Conservative Shelf-Life Estimates
During accelerated testing some drugs may degrade speedily but remain stable under the regular storage conditions. This may result in a shorter period than necessary being assigned, which in turn leads to wastage of product.

Accelerated stability testing methods:

Isothermal testing

The drug is tested at a constant elevated temperature which is higher than the usual recommended storage temperature. By maintaining a steady temperature one can measure the degradation rate, estimation of product shelf life and understand the drug stability profile under stress. Chemical reactions such as hydrolysis or oxidation can be studied by this method.

Example: A tablet formulation kept at 40ºC and 75% RH may show a reduction in active drug after 3 months, indicating potential shelf-life issues if similar conditions are experienced

Forced degradation studies

Forced degradation studies are designed and are essential to understand the intrinsic stability characteristics of a drug substance. Performing stress studies under variable conditions will predict formation of possible degradation products that may be obtained during long term stability testing ¹⁴ Based on this a method is developed and validated for drug substance and drug product. For a new Abbreviated New Drug Application (ANDA), forced degradation studies should be conducted and the resulting data incorporated into the validation of stability-indicating analytical methods.

Guidance on forced degradation used by industry comes from ICH, FDA and publications/reviews.

A) As per ICH guidelines

a) Acid and base hydrolysis

Acid and base hydrolysis involves degradation of a drug product under acidic and basic conditions which generates primary degradation products in a desirable range. Hydrochloric acid (0.1M to 1M) for acid hydrolysis and sodium hydroxide (0.1M to 1M) for base hydrolysis are suitable reagents. Stress testing generarally starts at room temperature (benchtop study). If there is no degradation, apply elevated temperature (50 ºC to 70ºC). At the end of sample removal acids are neutralized with a base with the same concentration, and vice versa, to stop the reaction and further degradation ⁶.

b) Oxidation condition

Hydrogen peroxide is a commonly used oxidizing agent for forced degradation studies. A study starts at room temperature and a concentration of 0.3 to 3%. Up to 20% degradation may generate significant degradation products. Electron transfer mechanisms involve the formation of anions and cations. Phenols, amines and sulphides are susceptible to electron transfer oxidation to give N-oxides, hydroxylamines, sulphones and sulphoxides ⁶.

3) Photolytic condition

Photolytic study must be conducted to demonstrate that exposing a drug product to light does not result in unacceptable change. Some primary degradants may be generated if the product is sensitive to light. As per ICH guidelines samples are exposed to a minimum of 1.2 million Lux hrs for visible light and 200 watt hours/m2 for UV light. The maximum exposure recommended is 6 million Lux/ hrs. Free radical mechanism was induced in this condition. Functional groups such as carbonyl, nitro aromatic, N-oxide, alkenes are likely to introduce photostability ⁶.

Thermal condition (e.g dry heat exposure and wet heat exposure) is carried out under more harsh conditions than recommended ICH Q1A accelerated testing conditions. Solid state samples can be exposed to dry and wet heat while liquid drug products are exposed to dry heat. At higher temperatures studies are conducted for a short period of time. The effect of temperature is studied through the Arrhenius equation:

where

A is the specific reaction rate, Eₐ is the frequency factor, R is the activation energy,

T is the gas constant (1.987 cal/deg⋅mol), and is the absolute temperature in Kelvin ⁵.

The thermal degradation study is carried out at 40ºC–80ºC.

Arrhenius equation demonstrates that a small rise in temperature can accelerate the degradation reaction.

Example: Some anticancer drugs such as Palbociclib show formation of unspecified degradation product when a sample solution is exposed to direct sunlight.

For the present study, a sample matrix was prepared for the development and validation of a stability-indicating HPLC method for the determination of organic impurities. An appropriate aliquot of this sample matrix was subsequently diluted to prepare the sample solution for the stability-indicating assay method. A mass balance table shows how much specified and unspecified degradation products are formed and how much the % assay has dropped from the initial value. As per ICH guidelines 5% to 20% degradation shall be achieved irrespective of the condition.

B) As per ANVISA (Brazil market)

ANVISA (Brazilian National Health Surveillance Agency) published the RDC53/2015 regulations where it outlines specific requirements for product registration and post approval changes with respect to identification, qualification and reporting of degradation products and expects that information to be included in the report. ANVISA primarily focuses on forced degradation studies for filing purposes to obtain,

Identification of functional groups which are responsible for major degradation pathways.
Assessing specifically designed FD experimental conditions and the duration.
Requirement for specific information to be captured in method validation report.
Considering the degradants from drug product manufacture and storage.
Safety qualification of degradant products.
Compliance with new regulations for approved products and post approval change submissions.

As per guidelines, a study shall be conducted on the drug substance as well as on the drug product ¹¹

Table-III: Comparative study of FD as per ICH guidelines and ANVISA

Study type	Condition	ICH	ANVISA
Stability indicating method	-	Required	Required
Study requirement on	-	Drug product and placebo	API, drug substance drug product and placebo
Sample treatment	-	Direct treatment or after extraction	Direct treatment
Acid Hydrolysis	0.1-1.0 N HCl	RT or by heating to (50ºC to 70ºC)	Few hrs to 7days at RT
Base Hydrolysis	0.1-1.0 N NaOH	RT or by heating to (50ºC to 70ºC)	Few hrs to 7days at RT
Oxidation	0.3-3% Hydrogen Peroxide	RT or by heating to (50ºC to 70ºC)	Few hrs to 7days
Oxidation	mM Fe III and Cu II solution at RT	Not required	1 to 7days
Thermal	70ºC or may vary if oxidation is expected	40ºC to 80ºC	Upto 3 weeks
Thermal/Humidity	70ºC/75% RH	At about 75% RH	Upto 3 weeks
Photo degradation	Fluorescent and UV light	Fluorescent = 1.2 million lux hrs UV = 200 watt hours/m²	> 2x of ICH
Amount of forced degradation required	-	5% to 20%	10% to 15%

Following forced degradation studies, a stability indicating method is developed and validated to quantify assay, specified degradation products, and unspecified degradation products. A mass balance table is then prepared demonstrating:

Mass balance = % Assay + % specified degradant products + % unspecified degradant products.

Well-designed mass balance ranges from 95-105 %, confirming the analytical method adequately monitors major and minor breakdown of product^[14].

A forced degradation study serves the following purposes:

1) It provides information on possible pathways of degradation and formation of specified or unspecified active degradation products and helps with structural elucidation of degradants.

2) Validation of analytical methods to ensure they can accurately detect and quantify degradation products in stability testing.

3. Use in Biopharmaceuticals

Biologics such as proteins, monoclonal antibodies and vaccines are complex and more sensitive than small molecular drugs. They are easily affected by temperature change, light, mechanical stress and moisture, which leads to the following changes:

a) Protein denaturation (loss of structure and function)

b) Aggregation (clumping of protein molecules together)

c) Deamination or oxidation (chemical changes)

By performing accelerated stability testing one can predict the behaviour of sensitive molecules during shipping and storage, which guides formulation that protects the drug. This includes the addition of stabilizers, selection of proper buffers and designing special packaging that controls temperature and light exposure^¹⁵.

Example:

Monoclonal antibodies are tested at elevated temperature and light to observe loss of potency or change in protein structure. This ensures that the drug remains effective and safe throughout the product life cycle

There are additional important ICH guidelines related to stability testing, such as:

· ICH Q1B: Focuses on testing how drugs respond to light exposure (photostability testing) (1996).

· ICH Q1E: Provides guidance on how to evaluate and interpret stability data (2003).

· ICH Q1F: Describes special testing designs called bracketing and matrixing, which help reduce the number of samples and tests without affecting quality (2006).

These ICH guidelines help pharmaceutical companies around the world perform stability testing in a standardized way, ensuring drug safety and quality for patients everywhere.

An overview of the China market for stability testing

The China market emphasizes stability studies of affecting factors in the testing of drugs.

Preparations for reference sample (innovator) and test sample^¹² are monitored under the influence of high temperature testing, high humidity testing and photo stability testing by strong light.

This study report covers following stress conditions:

a) Affecting Factors Testing with (Direct Exposure - Test Product)

i. Temperature (At 50ºC for 5days and 10 days)

ii. Photostability (UV –Visible light): The product is exposed to light with an intensity of

4500 lx ± 500 lx.

iii. Humidity (At 25°C/ 90% RH for 5day and 10 days in KNO3) and (At 25°C/ 75% RH for

5days and 10 days in NaCl)

b) Affecting Factors Testing (Exposure of with primary pack of Test product)

i. Temperature (At 50ºC for 5days and 10 days)

ii. Photostability (UV –Visible light): The product is exposed to the light with an intensity of

4500 lx ± 500 lx for 10days.

iii. Humidity (At 25°C/ 90% RH for 5day and 10 days in KNO3) and (At 25°C/ 75% RH for

5days and 10 days in NaCl)

c) Affecting Factors Testing with (Direct Exposure- Reference Product)

i. Temperature (At 50ºC for 5days and 10 days)

ii. Photostability (UV –Visible light): The product is exposed to light with an intensity of

4500 lx ± 500 lx.

iii. Humidity (At 25°C/ 90% RH for 5day and 10 days in KNO3) and (At 25°C/ 75% RH for

5days and 10 days in NaCl)

USFDA Regulations

The Unites States Food and Drug Administration (USFDA) follows International Council for Harmonization (ICH) guidelines for drug stability testing but also includes some additional guidelines specific to the US. USFDA focuses on collecting real-time stability data, which means testing drugs under normal storage conditions for the entire shelf life. Based on this data expiration dates are assigned. While accelerated stability data (testing drugs under harsh conditions within short period of time) supports tentative shelf lives, real time stability testing data is required for final approval of product shelf life.

WHO Guidelines

The world health organization (WHO) provides stability testing guidance especially for global health programmes and developing countries. As many tropical regions experience a hot and humid climate, WHO recommends that drugs intended for these areas are tested under Zone IV conditions (e.g., 30°C and 75% relative humidity).

Shelf-Life Extension Program (SLEP)

Shelf-Life Extension Programme (SLEP), managed by US FDA, has shown that many drugs remain stable and effective after their official expiration dates. This programme tested various medications which includes drugs that are used for diabetes, Parkinson’s, and Arthritis and found that their shelf lives could be extended significantly^³.

As an example, several batches of diazepam and ciprofloxacin were found stable and potent for more than 5 years beyond their labelled expiration dates.

Based on scientific stability data expiration dates are reassessed which can reduce drug waste, save cost, and improve medication availability, especially important in situations such as military stockpiles or emergency reserves.

Case Studies

The examples below demonstrate the behaviour of different types of drugs which are used in the treatment of the same disease and require unique stability considerations for safety and effectiveness.

1) Diabetes Mellitus Medications

Medications such as insulin and metformin need thorough stability testing as they are used widely and are essential for patient health.

a) Insulin

Insulin is sensitive to temperature as it is protein based. It should be stored in cold conditions to keep it effective. There is stability loss if it is stored to elevated temperature, which makes it less effective or unsafe. This highlights criticality for cold storage and handling during shipping.

b) Metformin

Metformin belongs to the Biopharmaceutical Classification system (BCS) Class III category, having high solubility and low permeability. Chemically Metformin is quite stable, however it can be affected by moisture. Excess moisture can cause changes that reduce shelf life. Moisture proof blister packs or bottles with desiccants are essential to protect Metformin and ensure quality during storage.

2. Parkinson’s Disease treatments

a) Levodopa

Levodopa is sensitive to oxidation; it breaks down when exposed to oxygen and light. This reduces drug efficacy, which affects symptom control in patients. To prevent this, light protecting packaging and addition of antioxidant excipients are used.

b) Dopamine agonist

These drugs may have different stability challenges but also require careful testing to ensure that they will remain effective over time.

3. Arthritis Medications

a) Methotrexate

This drug is sensitive to change in pH and exposure to light. To protect against this formulation designed to adjust the drugs pH environment and protective packaging is used that shields it from light.

b) NSAIDS (e.g Ibuprofen)

Exposure to high humidity lowers potency and leads to degradation. Moisture proof packing and storage conditions are essential to keep it effective over time.

Case studies for product recall/warning letter

1. Potassium chloride ER Capsules

One reputed pharmaceutical company recalled all of the batches of potassium chloride ER capsules from the US market after repeated failures during long term stability testing. The root cause was investigated and it was found that changes in increased formulation parameters contributed to failing of dissolution results up to 100 days after sample pull, delaying detections and leading to subpotent dosing for electrolyte replacement. An FDA warning letter was issued for inadequate root cause analysis and validation, leading to full market withdrawal and CAPA implementation^¹⁶.

2. Sodium acetate injection USP

Sodium acetate injections USP (400 mEq/100ml) were recalled from the market due to particulate matter observed in reserve and stability sample vials. Stability samples showed glass particulates from container closure interaction which led to vessel irritation upon IV administration.

Product was recalled which was distributed nationwide, highlighting the importance of stability in detecting physical degradation over time^¹⁷.

3. Tirofiban hydrochloride injection

Tirofiban hydrochloride injection (glycoprotein inhibitor) underwent class II recall due to out of specification stability results where potency loss or degradation before expiry had happened. After commercialisation it was observed that there was chemical instability in the parenteral solution, most likely from hydrolysis or precipitation under storage, compromising anti-platelet efficacy. This illustrates the need for bracketing stability studies in injectables to prevent subpotent dosing^¹⁸.

4. Paracetamol suspension

Two lots of paracetamol suspension were recalled in July 2024 and October 2024 due to discolouration, following chemical degradation assay and related substances failure. Stability issues highlighted uncontrolled humidity, temperature and excipient interaction which accelerated hydrolysis/oxidation in the liquid formulation rendering it potentially toxic and subpotent. Inadequate CAPA was declared after first recall leads to second one emphasizing root cause analysis in hot/humid conditions^¹⁹.

5. Losartan Potassium Tablets

One reputed pharmaceutical company recalled multiple tablet lots (50mg and 100mg) in 2019 due to unacceptable rise in levels of N-Nitroso-N-methyl-4-aminobutyric acid (NMBA), a nitrosamine impurity exceeding the limit. As the API is sourced from Hetero Labs, time-dependent formation of nitrosamines may occur due to residual solvents and/or process-related impurities, potentially increasing the risk of carcinogenic exposure despite the API’s high pharmacological potency. About 44 lots were recalled from Arab countries affecting millions of patients^²⁰.

Table-IV: Summary of recall cases/warning letter

Recall case	Mode of Stability failure	Factors
Potassium Chloride ER	Failure of dissolution	Process changes and long term stability delayed
Sodium Acetate injection	Particulate matter in stability vials	Container interaction
Tirofiban Inj	Potency loss/degradation OOS	Solution hydrolysis
Paracetamol Suspension	Discoloration/Assay failure	Humidity/Oxidation
Losartan Tabs	Nitrosamine impurity	API degradation

CONCLUSION

Comprehensive stability testing and understanding of factors affecting pharmaceutical product stability are foundational to ensuring patient safety, therapeutic efficacy, and regulatory compliance. This review has synthesized knowledge regarding: (1) intrinsic and extrinsic stability factors (temperature, humidity, light, pH, excipient interactions, polymorphism); (2) internationally harmonized regulatory guidelines from ICH, ANVISA, and China; (3) accelerated and forced degradation methodologies; and (4) real-world applications exemplified through case studies and product recalls.

Key insights from recent product recalls include: the critical importance of rigorous analytical method development and validation; the necessity of comprehensive root cause analysis for out-of-specification results; the role of supplier qualification and supply chain oversight in maintaining product quality; and the value of preventive strategies such as container-closure interaction studies and excipient compatibility assessments.

Looking forward, pharmaceutical scientists should continue to: (1) adopt emerging technologies and accelerated prediction models where appropriate; (2) maintain rigorous adherence to international stability guidelines while accounting for regional regulatory requirements; (3) implement robust quality systems, including trend analysis and CAPA procedures; and (4) recognize that stability is not merely a regulatory compliance exercise but a fundamental commitment to product quality and patient safety.

References

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