Stability Testing in Pharmaceuticals

BY
DR ASHISH KUMAR PARASHAR
Introduction
• Kinetics of stability in pharmaceuticals delves into the study of how
drug substances and drug products change over time under various
conditions.
• It is a crucial aspect of drug development and manufacturing, ensuring
the efficacy, safety, and quality of medications throughout their shelf
life.
• By understanding the factors influencing drug degradation, researchers
can optimize storage conditions, develop appropriate formulations, and
establish expiration dates, ultimately maximizing the therapeutic
benefits of medications while minimizing adverse effects.
 Importance of studying Kinetics
It determines-
• Stability of drug / half life of drug- defined as time necessary for a drug to
decay to its half life or 50% conc. (eg. 100% 50%, 50% 25%).
• Shelf life- defined as the time required for a drug to decay to 90% of its
original conc.
RATE AND ORDER OF REACTION
• The velocity with which a reaction or process occurs is called its rate.
• The Conc. of drug which influences the rate of reaction or process is called
its order of reaction. Drug A Drug B
• The rate of forward reaction is expressed by = - dA/dt
• As the reaction proceeds, the conc. of drug B increases & rate of reaction
can be expressed by= dB/dt
If C is the conc. of drug A as it is changed to B can be described by expression as a function of time t;

dC/dt = -KCn
where,
K = rate constant
n = order of reaction
if, n = 0 (zero order kinetics)
n = 1 (first order kinetics)

ZERO ORDER REACTION

Also called as constant rate process. The rate of reaction is independent of conc. i.e rate of reaction
cannot be increased further by increasing the conc. of reactant.

dC/dt= -K0C0--------------- eqn 1

where, K0 = zero order rate constant (in mg/min)

Rearranging eqn 1:
dC = -K0 dt --------------- eqn 2

Integrating the eqn 2:

C-C0 = -K0 t
Where,
C0 = conc. of drug at t = 0
C = conc. of drug yet to undergo reaction at time t

Graph of zero order kinetics showing relationship b/w rate of reaction and conc. of drug.
FIRST ORDER REACTION
• These are the reactions whose rate is directly proportional to conc. of the drugs undergoing reaction
i.e greater the conc., faster the reaction.
• It follows linear kinetics.
dC/dt = – KC-------------- eqn 3
Where, K= first order rate constant ( per hour)
Rearranging the above eqn 3,
dC/C = – Kdt--------------- eqn 4
Integrating the above eqn 4,
𝐥𝐧 𝐂 − 𝐥𝐧 𝐂𝟎 = −Kt

𝐥𝐧 𝐂 = 𝐥𝐧 𝐂𝟎 −Kt
In terms of log,
log C = log C0 − Kt/2.303

Graph of first order kinetics showing linear relationship b/w rate of reaction and conc. of drug.
Factors Affecting Pharmaceutical
Stability
1 Temperature 2 Humidity
Higher temperatures accelerate chemical Moisture can promote hydrolysis and
reactions, leading to faster degradation of other degradation reactions, especially in
drug molecules. This is why most formulations containing water-sensitive
pharmaceuticals are stored in cool, dry drugs. Proper packaging and storage
places. conditions are essential to minimize
exposure to humidity.

3 Light 4 pH
Exposure to light, particularly ultraviolet The pH of the formulation can influence
(UV) radiation, can trigger the stability of drug molecules. Each drug
photodegradation, leading to the has an optimal pH range for stability, and
formation of inactive or potentially deviations from this range can accelerate
harmful products. Many pharmaceuticals degradation.
are packaged in amber glass or opaque
containers to protect them from light.
Stability Testing
• Stability defined as capability of a particular formulation in a specific
container/closure system to remain within its physical, chemical,
microbiological, toxicological, protective and informational
specifications.
• It is the extent to which a product retains, within the specified limits,
throughout its period of storage and use, the same properties and
characteristics possessed at the time of its packaging.
SCOPE OF STABILITY TESTING
 Provide evidence as to how the quality of drug product varies with time.
 Establish shelf life of drug product.
 Determines recommended storage conditions.
 Determine container closure system suitability.
 TYPE OF STABILITY
• Chemical: Each active ingredient retains its chemical integrity and labeled potency within specified
limits.
• Physical: Includes appearance, palatability, uniformity, dissolution and suspend ability are retained.
• Microbiological: Sterility or resistance to microbial growth is retained according to specific
requirement.
• Therapeutic: Activity remains unchanged.
• Toxicological: No significant increase in toxicity.
Stability Testing Protocols
1 Long-Term Stability
Long-term stability studies are conducted under real-world storage
conditions to evaluate the product's stability over its intended shelf life. These
studies typically involve storing the drug product at room temperature and
analyzing it at predetermined intervals.

2 Accelerated Stability
Accelerated stability studies are conducted at elevated temperatures and
humidity to predict the long-term stability of the drug product in a shorter time
frame. These studies help identify potential stability issues early in the
development process.

3 Stress Testing
Stress testing involves exposing the drug product to extreme conditions, such
as high temperatures, high humidity, and acidic or alkaline pH, to study the
degradation mechanisms and identify potential degradation products.
Stress Testing Conditions
Thermal Stress Photolytic Stress Hydrolytic Stress
Thermal stress involves exposing the Photolytic stress involves exposing the Hydrolytic stress involves exposing the
drug product to elevated temperatures drug product to intense light, typically drug product to different pH conditions
to accelerate degradation. This helps UV radiation, to assess its sensitivity to to evaluate its susceptibility to
determine the drug's thermal stability light. This test helps ensure the hydrolysis, a common degradation
and predict its shelf life under normal product is adequately protected from pathway for many drugs.
storage conditions. light during packaging and storage.
Accelerated Stability Studies
Objective
Accelerated stability studies aim to predict the long-term stability of a
drug product under normal storage conditions by subjecting it to
elevated temperatures and/or humidity for a shorter duration.

Methodology
The product is typically stored at elevated temperatures, often 40°C,
and/or high humidity, such as 75% RH, for a defined period. The drug
product is then analyzed at regular intervals to assess its degradation
profile.

Data Analysis
The data obtained from accelerated stability studies is used to model
the degradation rate and predict the shelf life of the drug product under
normal storage conditions.
Analytical Techniques in Stability Testing

HPLC Spectroscopy Titration Mass Spectrometry

High-performance liquid Spectroscopic techniques, such as Titration is a chemical analysis Mass spectrometry is a sensitive
chromatography (HPLC) is a UV-Vis and FTIR spectroscopy, can method used to determine the and powerful technique used to
powerful technique used to provide information about the concentration of a substance in a identify and quantify drug
separate, identify, and quantify molecular structure and changes in sample by reacting it with a solution substances and degradation
drug substances and degradation the drug product during of known concentration. It can be products. It is used in stability
products. It is widely employed in degradation. These techniques are used to monitor the degradation of testing to monitor the degradation
stability testing to monitor the used to monitor the purity and drug products over time. of drug products and identify
degradation of drug products over integrity of the drug product. potential degradation products.
time.
Regulatory Requirements and
Guidelines
ICH Guidelines FDA Regulations
The International Council for The US Food and Drug
Harmonisation (ICH) provides Administration (FDA) has specific
guidelines for pharmaceutical regulations for pharmaceutical
stability testing, including stability testing, including
requirements for long-term, requirements for shelf life
accelerated, and stress testing. determination, labeling, and storage
These guidelines are widely adopted conditions.
by regulatory agencies worldwide.

EMA Guidelines
The European Medicines Agency (EMA) also provides guidelines for
pharmaceutical stability testing, which are similar to those of the ICH and FDA,
ensuring a harmonized approach to drug stability regulations.
 ICH GUIDELINE FOR STABILITY TESTING

Q1A Stability testing of New Drug Substances and Products (Second Revision)

Q1B Stability testing : Photo stability testing of New Drug Substances and Products

Q1C Stability testing of New Dosage Form

Q1D Bracketing and Matrixing Designs for stability testing of Drug Substances and Products

Q1E Evaluation of stability data

Q1F Stability data package for Registration Applications in Climatic Zones III and IV

Q5C Stability testing of Biotechnological/Biological Products

 CLIMATIC ZONES FOR STABILITY TESTING
Zone I (TEMPERATE)
• United kingdom, Northern Europe, Russia, United states.
• Long term testing conditions- 210C/45%RH
Zone II (SUBTROPICAL & MEDITERRANEAN)
• Japan, Southern Europe.
• Long term testing conditions- 250C/60%RH
Zone III (HOT & DRY)
• Iraq, India.
• Long term testing conditions- 300C/35%RH
Zone IV (HOT & HUMID)
• Iran, Egypt. • Long term testing conditions- 300C/65%RH
 TEST STORAGE CONDITION

Intended storage condition Study Storage conditions Minimum time period

covered

Room temperature Long term 25ºC ± 2ºC/60% RH ± 5% RH 12 months

Intermediate 30ºC ± 2ºC/65% RH ± 5%RH 6 months

Accelerated 40ºC ± 2ºC/75% RH ± 5% RH 6 months

Refrigerated Long 5ºC ± 3ºC 12 months

Accelerated 25ºC ± 2ºC/60% RH ± 5% RH 6 months

Freezer Long 20ºC ± 5ºC 12 months

 Shelf-Life Determination
Step 1 Conduct long-term and accelerated
stability studies to gather degradation
data.

Step 2 Analyze the data and determine the

degradation rate constant (k) and
activation energy (Ea) for the drug
product.

Step 3 Use the degradation rate constant and

activation energy to predict the time
required for the drug product to
degrade to an unacceptable level under
normal storage conditions.

• The time period during which a drug product is Step 4 Establish the shelf life of the drug
expected to remain within the approved shelf life product, typically as the time required
specification, provided that it is stored under the for the drug product to degrade to a
conditions. specific level, such as 90% of its initial
• The time period during which the drug maintain concentration.
its 90% potency or loss not more than 10%
potency.