Drug Stability
➡Physical Degradation of Pharmaceutical Products
➡Chemical Decomposition of Drugs Preventive Measures
➡Influence of Light on Drug Decomposition Effect of Temperature on Drug Decomposition
➡Chemical Stability Testing Dosage Forms.
➡Storage
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Drug decomposition or degradation occurs during storage because of chemical alteration (reaction) of the active ingredients or additives. The knowledge of chemical inetics is helpful to predict the rate of such reactions and furthermore to evaluate the shelf life.
Stability is officially defined as the time lapse during which the drug product retains the same properties and characteristics that it possessed at the time of manufacture. The stability of a product is expressed as the expiry period or technically as shelf life. Expiration period is a valuable quality attribute for all pharmaceutical dosage forms. The expiration date should be preferably accompanied by details of specific storage conditions as provided in the pharmacopoeia for this purpose (preservation, packaging, storage and labelling). Adequate stability data acquired by the manufacturer should be available to support the expiration period and storage conditions specified. A manufacturer is obliged to indicate the shelf life of a drug on the label unless it is greater than 3 years. No drug may be sold after 5 years.
Stability studies are necessary for the following reasons:
1. Product instability or chemical degradation of active drug may lead to under-medication due to lowering of the concentration of the drug in the dosage form. Examples are digoxin and theophylline. If concentration of drug is not maintained in the body (or blood) through an appropriate dose, the dosage form becomes ineffective.
2. During decomposition of active drug toxic products may be formed. For example, p-aminosalicylic acid (PAS) is converted into p-aminophenol, which is toxic. Infusion of degraded penicillin G causes adverse drug reactions, because of sensitization of lymphocytes and formation of antipenicilloyl antibiotics.
3. Instability may be due to change in physical appearance. Exam ples of this type are, mottling of tablets, creaming of emulsions or caking of solids in a suspension.
Drug Control Administration has taken steps in the public interest.At the same time, manufacturers have taken steps to conduct stability studies. In this process, the following advantages are perceived.
(a) Assurance to the patient:
The manufacturers prescribe the expiration period on their products. This is an assurance given by the manufacturers that the patient would receive a uniform dose throughout helf life.
(b) Economic repercussions:
Stability testing prevents the possi bility of marketing an unstable product. Heavy expenditure is involved in recalling a product from the market, when found unstable at a later period. It also costs the reputation of that company.
(c) Legal requirement:
The Drug Control Administration insists on manufacturers on conducting the stability studies, identity, strength, purity and quality of the drug for an extended period of time in the conditions of normal storage.
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