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kinetics of stability.pptx

• 1. Prepared by- Vivek Wagh Roll no – 15 FY ( Pharmaceutics ) Sanjivani college of pharmaceutical education and research Guided by- Dr. Abhijeet D Kulkarni Department of Pharmaceutics 1 4/20/2022
• 2. • Definitions • Rates and order of reaction • Molecularity of reaction • Zero order reaction • First order reaction • Second order reaction • Factors affecting rate of reaction • Kinetics of drug degradation 2 4/20/2022
• 3.  Chemical kinetics : It is the study of the rate of a chemical changes taking place during chemical reactions.  Drug stability : It is defined as the ability of a pharmaceutical product to maintain its chemical, physical, microbiological, and biopharmaceutical properties during the time of storage and uses by the patient.  Stability : It is the capacity of a drug substance to remain within the established specification to maintain its identity, strength, quality and purity throughout the retest or during expiration period. 3 4/20/2022
• 4. • Rate of reaction is the change in concentration of reactants or products per unit time. • Order of reaction is the sum of the concentration terms on which the rate of reaction actually depends. • The order of reaction determines the way in which the concentration of a reactant influences the rate of chemical reaction. 4 4/20/2022 B A
• 5. Continued… • The rate of forward reaction is expressed as: − 𝑑𝐴 𝑑𝑡 Negative sign indicates concentration of drug A decreases with time. • As the reaction proceeds, the concentration of the drug B increases and the rate of reaction can also be expressed as : dB / dt • If c is the concentration of drug A, the rate of decrease in c of drug A as it is changed to B can be described by expression as function of time t. where, 𝑑𝑐 𝑑𝑡 = −kcn k = rate constant n= order of reaction if n=0 , ( Zero order process ) 5 4/20/2022
• 6. • Molecularity is defined as the number of molecules or atoms that must collide simultaneously to give the products. • Stoichiometric equation is essential to decide the molecularity of a reaction. • Molecularity reactions are of three types :- i. Unimolecular reaction ii. Bimolecular reaction iii. Termolecular reaction 6 4/20/2022
• 7. • Zero order reaction is defined as a reaction in which the rate does not depend on the concentration terms of the reactants. It is expressed as, − 𝑑𝑐 𝑑𝑡 = 𝑘0 where ko is the specific rate constant for a zero order.  Example : Oxidation of vitamin A in an oily solution 7 4/20/2022
• 9. Continued… • HALF LIFE : It is the time required to reduce the concentration of the reactant to half of its initial concentration. t1 2 = 0.693 𝑘 • SHELF LIFE : It is the time required to reduce the concentration of the reactant to 90 percent of its initial concentration. 𝑡90 = 0.105 𝑘 9 4/20/2022
• 12. Temperature Nature of Solvent Catalysis Ionic Strength Dielectric Constant 12 4/20/2022
• 14. The principles that generally govern hydrolysis reactions may be listed as follows : • Drugs with ester and amide groups react with one molecule of water and undergo hydrolysis. Ester groups break faster than amide groups. • Drugs are either weak acids or bases. Therefore, these may be available as ionic forms or neutral molecules. Hydrolysis reac tion between ionic species proceeds faster than with neutral molecules (to a large extent it is solubility related phenomenon).  PREVENTION : i. pH ii. Suppression of solubility iii. Removal of water iv. Complexation 14 4/20/2022
• 15. • It involves the removal of electrons from a molecule. The general principles that govern an oxidation reaction is listed as follows : • The presence of atmospheric oxygen (also air) promotes the rate of oxidation. • Since oxidation frequently involves free radicals, chain reactions occur. Light provides the necessary energy to initiate the oxidation process. • The presence of trace metals also accelerate the rate of oxidation. • Drugs are either weak acids or bases. Therefore, these may be available as ionic forms or neutral molecules. Oxidation reaction between ionic species proceeds faster than with neutral molecules (to a large extent it is solubility related phenomenon). • Drugs which decompose by oxidation pathways are given below. Arachis oil, Vitamin A, Ethyl Oleate, Riboflavin, Clove oil , Vitamin B12, Cinnamon oil. 15 4/20/2022
• 16. i. Antioxidants ii. Chelating agents iii. pH iv. Oxygen free environment 16 4/20/2022
• 17. • Photolytic degradation occurs due to exposure to UV or visible light in the wavelength range of 300 – 800nm. • Photodegradation rates are directly dependent on the amount of incident radiation & on the amount of radiation that is absorbed by the compound. • Eg: Conversion of ergosterol to vitamin-D by UV light. 17 4/20/2022
• 18. Continued… • Drugs which undergo light-induced chemical degradation are called photolabile(photosensitive) drugs. • Photochemical reactions are usually complex and proceed in several steps. These reactions usually follow zero order kinetics. • Examples are chlorpromazine, reserpine and cochicine. 18 4/20/2022
• 19. 1. “The theory and practice of Industrial Pharmacy ”, CBS Publishers & distributors, 4th edition by Roop K Khar, S P Vyas, Farhan ahmed, Gaurav K Jain , ‘Kinetic principles and stability testing’. Pg.no. 1036-1060 2. “Textbook of Physical Pharmaceutics”, Vallabh Prakashan ,by CVS Subrahmanyam, ‘Chemical Kinetics & Drug Stability’ Pg.no. 13-65 19 4/20/2022
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