Stability programs overview for Pharmaceutical products

Importance of stability programs

Products must maintain their quality, safety, purity and efficacy throughout their specified shelf life conditions up to their nominated expiration date.

Stability studies are conducted to:

• Determine the time during which a product meets registered standards when stored under defined conditions (called accelerated studies)
• To show that the product remains within its expiry specifications throughout its proposed shelf life (called real-time studies)

The difference between release and expiry specifications must therefore take into account the results of stability testing.

The maximum permitted shelf life is normally five years,

Purpose of stability studies

The purpose of stability testing has two parts:

1. To provide evidence on how the quality of a drug substance or drug product varies with time under the influence of a variety of environmental factors, such as temperature, humidity, and light; and

2. To establish a retest period for the drug substance, or a shelf life for the drug product, and recommended storage conditions.

Stability and container closure systems

Stability testing should be conducted on the proposed dosage form that is to be included in the container closure system (including, as appropriate, any secondary packaging and the container label).

Stability and degradation products

Stability studies try to identify the presence of possible degradants in the active ingredient (API) or drug product matrix. Unwanted degradants may be toxic or may interfere with the effectiveness of the drug.

i. Origin of degradants in products and APIs

Degradants can come from a variety of sources over time, such as:

• Interactions with excipients in the product matrix
• Interaction with primary packaging through leaching or binding
• Chemical breakdown over time due to heat, pH, light and other factors,

ii. Stability indicating test methods

Chromatography (HPLC) is an important technique used for API and degradant analysis as it can separate, detect and quantitate degradants. These assays are known as stability indicating methods. With the appropriate detector sensitivity, column and mobile phase, stability indicating methods ere very useful for determining degradant concentrations.

Some degradents will have a chromophore which will make UV detection feasible.

iii. Forced degradation studies – method validation

Forced degradation studies are used to validate the analytical method as stability-indicating in nature. The forced degradation studies are necessary for the API testing method and will also have to be conducted for the formulated and packaged product.

iv. Accelerated stability studies

Accelerated (higher temperature) studies are useful to quickly determine degradants and to establish preliminary stability data for the formulation during development.

Forced degradation profile

This is a typical forced degradation profile.

Notice that the main active peak (5) elutes at 4,8min and the two main degradant peaks (1 and 2) at 3.8 and 2.9min.

This indicates that the assay can successfully separate active from degradant.

The assay then can be called stability indicating in nature and can be used in stability trials.

Peak 2 represents the main degradant and peak 1 is the secondary degradant.

Analyzing stability data – Kinetic models

A kinetic model for degradation could be used to theoretically predict the rate of decomposition of active drugs.

However, kinetic models might not be optimal as they don’t take into account some factors such as the matrix of a drug, or when there is only a single drug in a reaction.

Dissolution rate, particle formation, and other physical stability issues add further complicates.

There is no substitute for the shelf life being determined empirically, that is, using real time data for the formulated product in the final package.

Stability Protocols and schedules 

Types of stability studies

Two types of stability studies can be performed on a product:

Real-time (shelf life) studies are performed:

• Over the entire shelf life of the product
• At temperatures in line with maximum label recommendations for storage
• Using the final primary packaging
• To give a confirmation of stability over the real shell life time

Accelerated studies are performed:

• Over a shorter period of time (3-12 months)
• At elevated temperature/humidify conditions to represent an acceleration of the degradation
• To predict shelf life based on a shorter study period and are used to initially register the product

Real-time studies

Requirements:

• The formulation of the product on stability must be as per the registered details.
• Product on stability must be manufactured using all manufacturing steps.
• During stability, product must be in its registered container and closure. All testing should be performed on this product.
• Initially, at least three batches must be places on stability, followed by one batch per year.
• Where initial stability was performed on a pilot batch, three full production batches are still required for stability.
• Drug products of different strengths require at least three batches at minimum and maximum strengths.
• Temperature (25°C ± 2°C) and Humidity (60% RH +/- 5°C (if warranted) for minimum 12 months should be allowed in the studies.

Accelerated studies

Accelerated testing can be performed on development, plot, and validation batches.

Requirements:

• Use a validated stability indicating method
• One batch per study is sufficient, as batch-to-batch consistency is not trying to be established
• Temperature (40°C ± 2°C at least 10°C above the long-term recommendation) and Humidity (75% RH +/- 5°C (if warranted) for minimum 06 months should be allowed in the studies.

Significant changes

Significant changes to the product, indicating instability, can be defined as:

• 5% potency loss from initial (time zero)
• Degradant approaching or exceeding its specification limit
• Product exceeding its pH limit
• Dissolution exceeding its specification limit
• Deterioration of appearance and physical limits
• Failing lo meet specification at 40°C / 75% RH or at 30°C / 75% RH (ICH Guidelines)

If significant changes in degradation are noticed, then additional testing can be performed at an intermediate condition.

Importance of stability protocols

A stability protocol should be developed and approved by Development, the Laboratory and Quality/Regulatory Affairs in advance of any study commencing.

The protocol should address the following:

• Responsibilities for the trial
• Photostability and stress testing
• Selection of batches and formulations
• Container closure system
• Specifications for the product and tests to be conducted
• Bracketing and matrixing strategy
• Testing schedule (checkpoint matrix)
• Storage conditions and monitoring
• Proposed methods of data analysis and evaluation
• Management of deviations and reporting

Design of stability protocols

A protocol is required for each stability study with a closeout report once the study is completed.

The protocol would contain the following information:

Stability Trial Protocol

1. General Product information

• Name, source, manufacturing sites, and date of manufacture of drug substance
• Dosage form and strength, including formulation
• Composition, type, source, size of container and closure

2. Specifications and test methodology

• Physical
• Appearance
• pH
• Organoleptic
• Disintegration
• Chemical
• Chromatographic
• Dissolution
• Degradants
• Microbiological
• Total aerobic count
• Yeast and mould
  

3. Study design and plan

• Number of batches, dosage units
• Sampling points, duration, storage conditions

4. Stability data and information

• Individual data – means, standard deviations
• Tabulated data by storage conditions

5. Data analysis

• Rules for exclusion of data points
• Data, plots, graphics
• Results – statistical analysis, estimated expiry date

Bracketing

Both bracketing and matrixing for finished dose forms may be used in establishing trial designs. The ICH have a Guidance for this area, ICH Q1D.

Bracketing allows you to economise by excluding intermediate combinations in a trial design, for example, only testing the lower and upper strengths of formulations.

The bracketing design below is based on a product available in three strengths and three container sizes. Here, it should be demonstrated that the 15ml and 500ml high-density container sizes truly represent the extremes. Batches for each seeded combination should be tested at each time point as in a full design.

When does bracketing apply? 

Bracketing applies in the following situations:

• Where the drug is available in multiple sizes or strengths
• Range of container / fill sizes, but type same
• Range of dosage strengths with very closely related formulations (for example, tablets with different compression weights)
  

It is not applicable if the formulation is significantly different between strengths, for example, one contains the addition of excipient other than colour or flavoring.

The surface area / volume ratio, dead space / volume ratio, container wall thickness, and closure performance characteristics should be proportional among sizes. 

Testing frequency and checkpoints

i. Real-time studies

For products, frequency of testing in the long-term storage condition should normally be:

• Initially
• Every 3 months over the first year
• Every 6 months over the second year
• Annually thereafter through the proposed shelf life.

For real time product stability, 3 batches are usually tested initially then one batch per year thereafter.

ii. Accelerated studies

A minimum of three time points, including the initial and final time points (for example 0, 3, and 6 months), is recommended for a 6-month study.

iii. Intermediate Conditions

When intermediate testing is required due to significant changes, a minimum of four time points are required. For example, in a 12-month study, points would include 0, 6, 9, and 12 months.

Stability trial storage conditions

Storage conditions (with appropriate tolerances) should test thermal stability, and if applicable, sensitivity to moisture, or potential for solvent loss.

The trial should take into account the climatic zones that the product will be marketed in.

Zone 1: Temperature less than 20 ⁰C

Zone 2: Sub-tropical with possible high humidity, averaging 20.5 – 24 ⁰C

Zone 3: Hot and Dry

Zone 4: Hot and humid, averaging more than 24 ⁰C

Sensitivity to moisture or potential for solvent loss is not a concern for drug products packaged in impermeable containers that provide a permanent barrier to passage of moisture or solvent. Thus, stability studies for products stored in impermeable containers can be conducted under any controlled or ambient humidity condition according to the general case.

Active raw material (API) studies

For new drug (active) entities, the following information should be available:

• Degradation pathways
• Identity of degradation products
• Suitability of analytical procedures for quantitation of drug substance and degradation products.

Degradation Pathways

Where the degradation pathway of the active is unknown, and therefore the stability can’t be predicted, a forced degradation should be performed, including the effects of:

• Elevated temperature
• Susceptibility to moisture and oxidation
• Light
• pH (if the finished product is a liquid)

Finished dose forms

Stability studies should include testing of those attributes of the drug product that are susceptible to change during storage, and are likely to influence quality, safety and/or efficacy. The testing should cover, as appropriate:

• Appearance
• Physical [including weight and water gain or loss)
• Chemical, including pH
• Potency or assay, including degradant levels
• Biological
• Microbiological attributes
• Preservative content (for example antioxidant or anti-microbial preservative!
• Functionality tests (for example, a dose delivery system)
  

Include any in-use conditions, for example, the stability of opened packages in multi-dose products. 

Expected tests

Once the stability trial schedule has been designed, the appropriate testing to be performed at each time-point needs to be allocated. This will depend on the form and container closure system of the finished dose product.

ICH Guidance Q6A on Specifications provides direction on expected tests for APIs and Finished Products.

Physical and performance parameters

Tablets

• Appearance
• Odour
• Hardness
• Friability
• Moisture content
• Brittleness (hard gelatin capsules)
• weight gain or loss

Liquid formulations

• Appearance, colour
• Odour
• pH
• Clarity (solutions)
• Freedom from visible particulate contamination
• Resuspendability (suspensions)
• Viscosity
• Phase separation
• Weight gain or loss
• Preservative efficacy
• closure integrity

Injectable Products:

• Appearance, colour
• Sterility, pyrogenicity
• Preservative content and efficacy (chemical/biological)
• Particulates
• pH
• Container closure integrity
• Plug appearance and reconstitution time (freeze-dried products)

Ointments:

• Appearance and odour
• Viscosity
• Softening range
• Loss of water
• Physical and chemical homogeneity – separation
• Particle size distribution
• Particle formation
• pH

Oral Powders :

• Appearance
• Colour
• Odour
• Moisture
• Reconstitution time

Nasal Spray:

• Appearance
• Colour
• pH
• Clarity (solutions)
• Particulate matter
• Preservative and antioxidants
• Unit spray medication content, droplet size
• number of actuations
  

Presentation of stability results

While presenting stability results it is important to include:

1. Initial (zero time] results
2. All individual results, rather than an average
3. Fiducial limits per assay for bioassays
4. The result as a (%) of the nominal (labelled) content
5. Where applicable, individual dose unit variations
6. Wherever possible, quantitative results
7. Explanations of anomalous or unusual results
8. Identify significant changes in assay method
9. Summaries/explanations of the data; rationale for exclusion of data

Review the results after each time point to highlight failures or unusual trends.
Investigate any failures using out-of-specification procedures. 

Stability Results and Shelf Life

General stability trial design

When designing a stability study, consider the following points:

• Accelerated studies do not necessarily follow kinetics, so extrapolation is often unreliable
• For long-term studies, data can be transformed to get linearity
• Three botches must be tested to assess batch-to-batch variability
• The number of replicates can be tested within a time checkpoint (removes assay-to-assay variation
• Maintain the same number of duplicate estimations at each checkpoint if possible
• Schedule additional assays at the final checkpoint
• Place more samples on trial than required to cover repeat tests
  

Evaluating results of the stability study

A systematic approach should be adopted in the evaluation of summary stability data and results. The data and results should include, as appropriate, results from the physical chemical biological, and microbiological tests, including particular attributes of the dosage form [for example, dissolution rate for solid oral dosage forms).

The degree of variability of individual batches affects the confidence that a future production batch will remain within specification throughout its shelf life. 

Physical:

• appearance
• color

Chemical:

• PH
• Assay
• Degradants
• Dissolution

Biological:

• Preservative
• Sterility
  

Typical problems with stability studies 

Inadequate specification of product and batches

The following issues can cause the trial to be rejected if the product and batches are not clearly defined:

• Failure to specify the formulations used in the trial, and to state which batches were identical to the registered formulations.
• Failure to state whether the batches used in the trial were pilot or production batches.
• Failure to describe clearly the packaging used in the trial and whether it is identical to the pack which will be sold.
  

Inadequate specification of trial design

• Failure to accumulate stability data on more then one batch.
• Failure to accurately define the temperature, lighting and humidity conditions applied during the trial.
• Failure to include information on the physical characteristics of the product during storage.
  

Inadequate specification of test methods

• Failure to describe test methods, or provide validation data on test methods, or even to validate the test methods.
• Using an HPLC procedure to detect impurities without validation of the method for that purpose, or the method only being validated for the active ingredient.
• The methods developed for active ingredients are often unsuitable for the separation of impurities / degradation products. The method must be validated for impurity detection.
  

Inadequate monitoring of trials

• Failure to conduct studies under the correct humidity conditions.
• Failure to conduct additional testing into obvious changes in the physical characteristics of the product during storage, such as a colour changes. Colour changes could indicate the formation of degradation products.
  

Inadequate in reporting and evaluating results

• Use of expressions such as “Passes Test” instead of figures.
• Deleting out-of-specification points without investigation.
• Failure to provide data from each time check point to assist in the assessment of trends.
• Failure to include either quantitative or semi-quantitative data on degradation products.
• Failure to provide results for individual dosage units.
• Attempting to extrapolate data obtained beyond reasonable limits.
• Failure to comment or conduct further testing when there is a lack of mass balance between the formation of degradation products and loss of the active substance. For example, is the product volatile, or is it absorbed on to the walls of the container?
  

General rules for nominating shelf life

General rules for evaluating stability data and nominating shelf life include:

• If no trends are noted after storage for a period of (x) months at an elevated temperature (at least 10C above the maximum storage temperature proposed for the product), then on interim shelf life of a maximum of 2(x) months may be permitted, where 2(x) does not exceed 3 years
• Shell lives of longer than 3 years should be supported by data on production batches stored at the maximum recommended temperature for the duration of the proposed shelf life
• Stability trials involving at least two production batches stored at the maximum recommended temperature should in any case be continued for the full period to validate the predicted shelf life

Interim shelf lives may be extended through submission of additional data accumulated in the later stages of the trial.

Calculating shelf life

After a study is completed, shelf life can be predicted from the data by the following methods:

1. Statistical analysis, unless obviously within limits
2. If analysis shows small batch-to-batch variability, combine all batches into one overall estimate (use p=0.25 to test variation)
3. Regression analysis and 95% lower confidence limit
4. Transform date into linear relationship, if needed
5. Goodness-of-fit on individual and combined methods to test assumptions of linear models

Stability indicating methods

• Don’t assume that pharmacopoeial methods are stability indicating
• Test methods should be fully described and validated
• If changes are to be made to the assay or other test method during a stability study, it may be difficult to compare results before and after the change
• If two methods are used in the study, compare their accuracy, precision, and specificity
• Changes to dissolution test methodology during stability testing programs are strongly discouraged
• Assays must validate accuracy, precision, linearity, specificity, LOD and LOQ for degradants
• Degradation products present at ≥ 0.5% of the active content should usually be identified
  

Test methods for stability studies

If an assay is to be used for stability testing, its validation needs to evaluate its stability indicating nature, particularly with regards to specificity.

The assay should be selective for degradance, not be interfered by matrices, have a defined degradation scheme for all active ingredients, and have a mass balance calculation with an aim of >90% contents accounted for.

Stress testing can be performed in order to determine the degradance. This involves submitting one batch of the active to acid-base hydrolysis, temperature exposure, and exposure to light and oxidising substances.

Microbial stability of products

As well as chemical stability, the microbial stability of products should be assessed by performing the following assessments:

• Preservative efficacy
  
  • traditional methods
  • challenge testing or PET test
• Chemical stability of the preservative
• If a product is multi-dose, simulate the conditions of consumer use, that is, opening and closing studies.

Microbial challenges only need to be performed at the start, annually, and end of the study. However, chemical assay of preservatives should be performed at more regular time points.

Microbial recovery methods should be validated before use in a stability study.

Sterility testing of sterile products is usually performed at the start, 12 months and end of shelf life. Pyrogens/endotoxins should be tested at the start and at the expiry date.