Trở về d_bb  ĐHKH


Trở về Trang Tc Giả




Gio Sư T Đồng


Sơ Lược Về Thử Nghiệm Sự An Định Của Dược Phẩm

Bi 1

Bi 2


































Main Menu





GS Tiến Sĩ T Đồng

Khoa trưởng
trường Đại Học Dược Khoa Si Gn



Bi 2 :



An Overview for Drug Stability Testing

Dong To, D.Sc.




            In the last step of the product/process development, the main objectives of the Formulation group are optimizing the drug delivery system and increasing the stability of a drug product. When the process is validated, then the testing of drug stability in the Manufacturing group will insure that the medicine retain its identity, strength and quality in the market throughout the period up to the expiration date.


The knowledge in many areas of the drug such as potency, metabolism, and physical/chemical/biochemical pathways allows the rational development of analytical methods for the expiration dating.


In this overview, some principles, practices and stability testing guidelines from the FDA of the US are briefly presented.




It is note that one could find in literature various examples of drug formulation using trehalose and hydrophobic sugar glasses (1), liposomes (2, 12), cyclodextrins (3, 19), of chemical kinetics and drug stability (4, 5, 6, 7), and of expiration dating and shelf life estimation (8, 9, 10). Also, one can get considerable amounts of updated information in the web sites of FDA including the FDA modernization act of 1997 (FDAMA) (13, 14, 15) and in that of the European Agency for the Evaluation of Medicinal products EMEA (16). In addition, one can have relevant services as provided by many independent labs (17, 18, 19, 20).


1.  Definition:


The stability means compliance of the drug product within the specifications. The stability testing insures the quality of the drug product as defined by its content of active ingredient, its purity and its organoleptic, physicochemical and biological properties. The drug could be a chemical, a biologic or a medical device. In general, biologics depend mostly on optimum formulation and good storage conditions for stability.


2.  Measurement:


The methods used to assess and control stability are based on rate constants of degradation reactions of the drug.


The shelf life of the drug can be calculated if the rate of loss "k" of the drug with time at storage temperature is known.


If [A]0 and [A]t are the initial active concentration and the residual active concentration at time t, the following rate equations describe the usual models:


zero order:                     [A]t             =  [A]0 - kt

first order:                      Ln [A]t        =  Ln [A]0 - kt

second order:                 1/[A]t          =  1/[A]0 + kt


The drug product expiration dates are usually based on assumed zero- or first-order kinetics. The shelf-life t0.90 is the time at which decomposition reaches 10% or activity decreases to 90%. The time should be determined at which the 95% one-side lower confidence limit for the mean degradation curve intersects the lower acceptable specification limit (appendix 1). This will assure that the average drug characteristics of the batch are within specifications up to the end of the expiration period.  




1.  General Product Information:


The basic information of the drug must be presented:


Dosage form.




Container-closure: composition, type and  size.

2.  Specifications and Test Methodology Information:


The specifications on physical, chemical, biological and microbiological characteristics of the drug must be described. A definition of potency is usually needed for biological activity of a drug.


The analytical methodology should be validated and presented with method accuracy, precision and suitability (11).


The method measuring the trace amount of harmful by-product or unwanted degraded product during drug storage should be known with acceptable limit of detection.


3.  Study Design and Study Conditions:


The sampling plan, number of units and sampling times are selected according to statistical quality control methods.


The testing of drug products for reconstitution at the time of dispensing (as directed on the labeling) must be defined. The same requirement is needed after they are reconstituted.


The duration of the study and storage conditions: temperature, humidity and light should be specified. For example, the Human Medicines Evaluation Unit of the EMEA defined significant change as failure to meet the specifications with long term testing, at temperature 25o 2o C and relative humidity 60% 5% RH for 12 months, and with accelerated testing at 40o 2o C and 75% 5% RH for 6 months.


4.  Stability Data/Information:


The lot number from research, pilot or production must be provided with the corresponding manufacturing date. The age of the bulk/active substance used in the testing should be mentioned. The analytical data and source of data points must be defined.


All relevant information of previous formulations or container-closure systems should be provided.


5.  Data Analysis and Conclusions:


The appropriate statistical methods and formulae used in the analysis must be documented. The calculations, statistical analysis and graphs to evaluate data should be provided. The results of statistical tests for potency estimates as well as the proposed expiration date and its justification must be presented.


The release specifications are defined to warrant an acceptable minimum potency at the initial release for full expiration dating period. 




1. Real-time stability:


This stability study at storage condition is the most reliable, but unfortunately it takes a long time and is very costly in the development phase of the drug.

2. Accelerated stability: 

The accelerated stability study predicts the expiry date using exaggerated storage conditions. The drug substance can be stressed as many ways as possible, using temperature, humidity, light, pH, solvents, buffers etc


The rate constant k is observed to have an exponential dependence on temperature. Where k is the reaction rate constant of any order, A and Ea are constants, and T is the absolute temperature, according to Arrhenius: 

k = A exp(-Ea/RT) 

The activation energy -Ea can be calculated as equal to R*Slope with R = Gas Constant = 1.987 cal K-1 mol-1. 

The activation energy Ea is an energy barrier of the system that the reactants must pass before becoming products. The usual range of Ea is about 12 to 24 kcal/mol, with hydrolysis: 14-20 kcal/mol and oxidation: 23 kcal/mol. 

The Ea depends on formulation, for example: the phenylbutazone in water has three rates: k1, k2, k3 of oxidation/hydrolysis corresponding respectively to Ea1, Ea2, Ea3 of 24.4, 26.7, 36.2 kcal/mol. In solvent such as dimethyl formamide, diethyl carbinol, propylene glycol, the Ea s are lower, from 3.9 to 7.7 kcal/mol, giving a shorter shelf life, only from 18 days to 113 days. 

The QdT factor, ratio of reaction rates at two temperatures differing by dT degrees, can be calculated as: 

C, knowing shelf life at higherThis factor is used to predict shelf life at 4 temperature. Usually, Q10  C equals to 2, 3 and 4 with to 30from 20 Ea s from 12.2 to 24.5 kcal/mol. This means that the rate increases  C.C from initial rate at 06 to 32 times at 2525C from initial rate at 0 C. 




The rate and order of reactions of some drugs are presented with kinetic models:


1.  Zero order:      [A]t = [A]o - kt


Aspirin suspension Salicylic acid +Acetic acid



k = 0.0075 mol l-1d-1 or 1.5% d-1

t0.90 = 6.67 days


2.  First order:      Ln [A]t = Ln [A]o - kt


Benzocaine 4-Aminobenzoic acid+ Ethanol



k = 0.05 w-1

t0.50 = 0.693/k = 13.86 weeks


3.  Second order: 1/[A]t = 1/[A]o+ kt


Pr-Paraben Hydroxybenzoic acid diethylamide + Propanol



k = 0.012 mmol l-1 w-1

t0.90 = 0.926 weeks


4.  Other kinetic models:


First order reversible kinetics

Photochemical Isomerisation [A B]



Competitive first order degradation

Hydrolysis/Rearrangement   [C A B]

O-Acetyl Propanolol


Sequential first order kinetics

Rearrangement/Hydrolysis   [A B C]

Betamethasone 17-Valerate


5. Analysis of a Monoclonal Antibody MoAb degradation study:


An example of accelerated testing using temperature to predict stability of a monoclonal antibody MoAb against carcino-embryonic antigen CEA is described. Samples are stressed at 37oC and the percent immunoreactivity % IR are recorded as follows:


Test samples:

MoAb in 140mM Phosphate, pH 8.5, 37oC


Sample ID                      % IR 

0 week                           95.8  

1 week                           89.8  

2 weeks                          88.4  

3 weeks                          75.8  

4 weeks                          75.6  

5 weeks                          66.3  

6 weeks                          62.6  

7 weeks                          58.5  

8 weeks                          51.7  


Kinetic model:


Different models are tested and results are tabulated in the following paragraph:


MODEL               R                          [IR%]O                  SS


Zero order            0.9907989            95.9                      34.1

1st order                0.9897601            98.2                      44.1

2nd order               0.9812260            102.3                    100.1




The best model describing the degradation of this monoclonal antibody is the zero order kinetics. It gives the highest correlation coefficient R of 0.9907989, the closest estimated initial %IR of 95.9 and the smallest sum of squares SS of 34.1.


The percent immunoreactivity of this monoclonal antibody replaces its potency in the calculation of loss of activity with time. The antibody vials at up or inverted positions of storage are used to detect effect of stoppers, but no difference has been found. The testing temperatures are 22oC, 37oC and 45oC. All physical, chemical, biological and microbiological characteristics of this antibody are tested at time intervals, but only results for activation energy, rate constants and shelf-lives at various temperatures calculated using Excel program are presented in appendix 2. 


6.       Some calculation programs used in the Stability Study:

Any of the following software could be used: RS/1 from BBN, Statistical Analysis System SAS, Excel PC, Q-basic or Irwin's computer solutions.




Some aspects and examples of the drug stability testing are presented. The accelerated testing to predict expiry dating of a monoclonal antibody against CEA is described. In a dosage form, each drug substance represents a particular case and should be treated accordingly. A good formulation could only be obtained by a team effort of many scientists in the product/process development phase.







1.     Trehalose and novel hydrophobic sugar glasses in drug stabilization and delivery

Gribbon et al., 1996


2.     Stealth liposomes, Microencapsulation

Lasic D.D., 1996


3.     Cyclodextrins: Drug solubilization and stabilization

Loftsson T. and Brewster M.E., 1996


4.     Chemical kinetics and drug stability

Guillory J.K. and Poust R.I., 1996


5.     Expiration dating of pharmaceutical compounds in relation to analytical variation, degradation rate, and matrix designs

Natarajan J., Altan S. and Raghavarao D., 1997


6.     Shelf life estimation for multifactor stability studies

Chen J.J., Ahn H. and Tsong Y., 1997 


Books/ Journals


7.     Stability Testing of Drug Products

Wolfgang Grimm

Wissenchaftliche Verlagsgesellschaft mbH Stuttgart 1987

Scientific Criteria, guidelines and official state requirements in Europe, Japan and USA.


8.     Accelerated Testing

Wayne Nelson

John Wiley & Sons, 1990

Statistical Models, Test Plans, and Data Analyses


9. Drug Stability, Principles and Practices

Second edition

Jens T. Carstensen

Marcel Dekker, Inc., 1995

Principles and practices of achieving drug stability


10. Stability of Protein Pharmaceuticals

Center for Professional Advancement

Course Director: Dr. Christopher Rhodes

Drug product stability

Protein stability

Protein preformulation/formulation

Accelerated stability tests.


11. Statistical Methods in Analytical Chemistry

Peter C. Meier and Richard E. Zund

John Wiley & Sons, 1993


12. The Pharmaceutical Journal

(official journal of the Royal Pharmaceutical Society of Great Britain)

Vol 269 No 7216, p: 414-417, 21 September 2002

British Pharmaceutical Conference 2002 summary



Web sites:


13.  www.fda.gov/cdrh of the Center for Devices and Radiological Health (CDRH), regarding pre-market approval application PMA, PMA supplements, pre-market notifications (510k) for Devices and post market surveillance (PS) submissions.


14. www.fda.gov/cder/guidance of the Center for Drug Evaluation and Research (CDER), summarizing the design and analysis of the real-time and accelerated stability studies applicable to chemicals, biologics and medical devices.


15.  www.fda.gov/cber/guidelines of the Center for Biologics Evaluation and Research (CBER), listing Guidance/Guidelines/Points to Consider. The guidances are listed in order by date, with the most recent guidance added to the top.


16.  www.emea.eu.int/pdfs/human/ich of the European Agency for the Evaluation of Medicinal products (EMEA), describing Stability Testing Guidelines: Stability Testing of New Drug Substances and Products. The Human Medicines Evaluation Unit defined significant change as failure to meet the specification with long term testing and accelerated testing. The International Conference on Harmonization (ICH) presented a Harmonized tripartite guideline for EC, Japan and USA.


17. www.magellanlabs.com/services/drugsubs of Magellan, listing all comprehensive analytical services for drug substance testing. This independent lab offers degradation chemistry and development of methods for drug stability.


18. www.cabrillolabs.com/capabilities/formulations.htm of Cabrillo providing excipient compatibility assessments in formulation development. Magellan Laboratories Cabrillo Facility offers packages to support pre-formulation and formulation development.


19. www.captosol.com/cycl/vollss.pdf from CyDex, Inc. specializing in the commercialization of modified cyclodextrins for use in drug development and formulation.


20. www.quintiles.com/Product_Development/Early_
Development/Stability_Testing.htm  from Quintiless Pharmaceutical Sciences: Stability Testing, Design Stability Protocol for investigational new drug IND and new drug application NDA This company provides extensive service for testing stability and storage capabilities






Gio Sư T Đồng
Khoa trưởng
trường Đại Học Dược Khoa Si Gn