Accelerated Stability Testing of dosage forms ……… A measure of how a pharmaceutical product maintains its quality attributes over time

Stability protocol Study Storage condition Long Term 25º C ± 2º C Minimum time period covered by data at submission Long Term (Ambient) 25º C ± 2º C 60%RH ± 5% 12 months Intermediate (controlled) 30º C ± 2º C 6 months Accelerated 40º C ± 2º C 75%RH ± 5%

According to ICH guidelines, The ambient study for drug product must be continued for a sufficient period of time beyond 12 months to cover the shelf life of the product. Intermediate storage condition data are required when a significant change occurs prior to completion of study under the accelerated storage condition. The accelerated storage condition must be >15º C above the ambient storage conditions.

Testing Frequency: For Long term testing, during first year sampling should be done every three months, during second year, sampling should be done every six months and after two years, sampling should be done once a year. Accelerated testing should be done atleast six months and it suggests sampling points of 0, 3, 6 months.

Accelerated Stability Studies Stability study to predict the shelf life of the product, by accelerating the rate of decomposition, preferably by increasing the temperature of reaction conditions. With the advancement in branch of kinetics, shelf life of a dosage form can be predicted within months based on accelerated stability reports Preparations are subjected to high stresses during stability testing. Common high stresses include : Temperature Humidity Light

Arrhenius equation It explains the effect of temperature on rate of a reaction. According to Arrhenius, for every 10º rise in temperature, the speed of reaction increases about 2-3 times. k = A e -Ea / RT Ideal gas constant Arrhenius factor Energy of activation Arrhenius factor is the frequency of molecular collisions occuring between the molecules. Log k = log A – Ea / 2.303 RT

Estimation of k value The reaction is conducted at several temperatures. Concentration of reactants is determined. Appropriate graphs are drawn for the kinetic data. Data is processed for all the orders. The order of the reaction is identified. From the slopes of the lines, k values are calculated for all temperatures.

Estimation of energy of activation A graph can be drawn by taking log k on y-axis and reciprocal temperature (1/T) on x-axis. A straight line is obtained, the slope of the line is negative and the magnitude is Ea / 2.303 R. The intercept corresponds to log A All the constants in the Arrhenius equation can be obtained from the graph. Activation energy is the minimum energy that a molecule should possess so that the molecular collisions produce the product.

Steps involved in Accelerated Stability Testing Steps involved in prediction of shelf life

The Preparation is stored at different elevated temperatures, to accelerate the degradation Samples are withdrawn at different time intervals The Order of the reaction is determined by plotting the appropriate function of concentration against time and linear relationship is determined Straight line in a graph permits the estimation of k value from the slope Similarly graphs are drawn for different elevated temperatures. K value for each temperature are calculated. By using Arrhenius relationship, Log k values are plotted against reciprocal of absolute temperature, energy of activation can be calculated.

Extrapolate the straight line to room temperature (k25) or refrigerated temperature and read the log k value on y-axis. Substitute the k value in the appropriate equation to get the shelf life of the product.

Arrhenius plot for predicting the rate constant at ambient temperature(25ºC).

Overview of storage conditions and storage period for solid, semisolid, and liquid dosage forms Stability investigation Organoleptic and physicochemical stability Photostability Chemical stability Dosage form Solid Semisolid Liquid All Storage condition Storage in open container until equilibrium is reached at 25ºC/60%,30ºC/70%, 40ºC/75% 5ºC ≥ - 10ºC 5ºC -40ºC Temperature cycle within 24 hrs 40ºC(content uniformity) ≥ -10ºC Xenon lamp 40ºC, 50ºC, 60ºC, 70ºC 30ºC, 40ºC, 50ºC Storage period 1-2 weeks 4 weeks 2 weeks 3 months 4 Weeks 48 hrs

Bracketing system for Dosage forms Dosages 1-2 3-4 >4 Samples tested All Highest Lowest Highest Middle Lowest

Packaging material:in selecting packaging material, the following has to be considerd Packaging materials permeable to water vapor result in a falsification of the results for semisolid and liquid dosage forms if varying degrees of weight loss occur that leads to differences in the active ingredient concentration or ion strength. The use of inert standard packaging materials that are impermeable to water vapor is important precondition for stress tests that are evaluated in terms of reaction kinetics, and on the results on which stability predictions are to be tested.

Most of the stress tests are carried out in standard packaging material. The following standard packaging materials are used: Solid dosage forms: 50-mL glass container with twist-off closure polypropylene tube Semisolid dosage forms: Standard tube, small volumetric flask, Aluminum tube, inert internal lacquering Liquid dosage forms: 25mL volumetric flask with ground-glass stopper However, furture investigations for the selection of the final packaging are necessary.

Selection of packaging material for solid dosage forms. On the basis of the results of the stress tests for solid dosage forms, the sensitivity to moisture can be determined and suitable packaging materials can be selected. As a rule, no interactions are to be expected. If the final packaging material has been selected and samples packed in the final packaging material are available, the investigation of photostability should be performed. Photostability :The samples with and without container are irradiated with a Xenon lamp for 24 hours.

Selection of packaging material for semisolid dosage forms. Packaging: Aluminum tube internally lacquered, plastic tubes. Problems: Corrosion , permeation, sorption. Tests packaging material – dosage form: To test for corrosion ,the filled metal tubes are stored horizontally upright and inverted at 400C, for 3 months and are then investigated. To test for permeation and sorption the filled plastic tubes are stored for 3 months at 500C, 400C, 300C/70%. If the final packaging material has been selected, the investigations on the photostability are performed.

Selection of packaging material for liquid dosage forms Packaging ampoule, injection vial with rubber stopper, glass bottle or plastic bottle with screw closure. Problems: leakage. To test for permeation, and leakage, the finale formulation solution is filled in the container, and for desorption placebo solution is used. The samples are stored vertically and inverted under 500C, 400C, 300C/70% for up to 12 weeks. Tested intervals: 0, 1, 2, 3 months. If the final packaging material has been selected the investigations on the photostability are performed.

Accelerated Stability Testing in Emulsions An emulsion is stored at elevated temperature. This decreases viscosity of the continuous phase. If the emulsion withstands this stress it is assumed to be stable at normal conditions of storage. Centrifugation Method: Creaming and flocculation are slow processes. Centrifugation accelerates rate of creaming and flocculation in emulsions. The emulsion is subjected to different centrifugal speeds and separation of phases is observed at different time periods. Bad emulsion separates oil instantly. Good emulsion does not exhibit detectable separation of oil phase until certain time period.

Accelerated tests for Suspensions Cake formation is accelerated by centrifugation. High speed centrifugation is hence not preferred, low speed centrifugation is used to study the physical stability. A Freeze-Thaw cycling technique is one of the stress testing . This cycling treatment promotes particle growth and has primary importance for changes in absolute particle size, particle size distribution and crystal habit.

Accelerated Tests for moisture absorption In this method, products are placed in an environment of high relative humidity and controlled temperature. Their physical and chemical stabilities are assessed. The results will indicate whether the product is susceptible to moisture and also whether the container needs to provide a high degree of protection.

Limitations Stability predictions based on Arrhenius equation are valid only when the break down depends on temperature. The energy of activation obtained in the study should be between 10 to 30 kcal/mole. When degradation is due to Microbial contamination Photochemical reactions When the product looses its physical integrity at higher temperatures. When the order changes at elevated temperatures. In case of disperse systems, when temperature is elevated viscosity is decreased and this may introduce errors in the prediction of stability.

Addition of Overages Excess amount of the drug can be added to the preparation to maintain 100% of the labelled amount during the shelf life of the product. Overages are calculated from the accelerated stability studies and added to the preparation at the time of manufacture. They should be within the limits compatible with the therapeutic requirement. Addition of overages doubles the shelf life of the product. Overages are added in multi vitamin preparations

110% 1 Year 2 years 100% 1 Year 90%

Conclusion Knowledge of stability of a formulation is very important for three primary reasons: A Pharmaceutical product must appear fresh, elegant and professional for as long as it remains on the shelf. Since some products are dispensed in multiple dose containers, uniformity of dose of the active ingredient over time must be ensured . The active ingredient must be available to the patient through out the expected shelf life of the preparation. A breakdown in the physical system can lead to non availability or of the medication to the patient. Conclusion

References : Patrick J.Sinko , Martin’s Physical Pharmacy and Pharmaceutical Sciences. Theory and practice of Industrial Pharmacy - Lachman International Stability Testing Drug stability- Cartensen C.V.S Subrahmanyam www.google.com

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