Jawaharlal Nehru Technological University Hyderabad B.Pharmacy II Year PHYSICAL PHARMACEUTICS-II Previous Question Paper (August - 2021 - R17)

Stabilization against hydrolysis involves minimizing contact with water or controlling the reaction environment. Strategies include: 1. Replacement of water with non-aqueous solvents like propylene glycol or alcohol. 2. Adjustment of pH to the range of maximum stability for the specific drug. 3. Solid state formulation, such as using dry powders or capsules instead of aqueous solutions. 4. Use of complexing agents like cyclodextrins to shield the drug molecule. 5. Control of temperature, as hydrolysis rates increase with heat.

Stabilization against oxidation involves preventing the initiation and propagation of free radical reactions. Strategies include: 1. Use of antioxidants such as ascorbic acid (water-soluble) or butylated hydroxytoluene (oil-soluble) to act as chain terminators. 2. Removal of oxygen by purging containers with inert gases like nitrogen or carbon dioxide. 3. Use of chelating agents like EDTA to sequester heavy metal ions that catalyze oxidative degradation. 4. Protection from light using amber-colored glass or opaque packaging to prevent photo-oxidation. 5. Maintaining low storage temperatures to reduce the kinetic energy of reactants.

Chemical degradation of pharmaceutical products is influenced by various physical and chemical factors that alter the stability of the active pharmaceutical ingredient (API).

Physical Factors:

• Temperature: According to the Arrhenius equation, the rate of degradation increases significantly with temperature. Higher temperatures provide more kinetic energy, increasing the frequency of molecular collisions.
• Light (Photolysis): Exposure to UV or visible light can trigger photochemical reactions, leading to the formation of free radicals or molecular rearrangement, especially in photosensitive compounds.
• Humidity/Moisture: For solid dosage forms, moisture can act as a reactant for hydrolysis or facilitate the migration of incompatible excipients.
• Solid State Properties: Particle size, crystalline form (polymorphism), and surface area affect the exposure of the drug to the environment and its reactivity.

Chemical Factors:

• pH: The pH of the medium is critical for drugs susceptible to acid-base catalysis. Most drugs exhibit a specific pH range where their degradation rate is at a minimum.
• Solvent Effects: The dielectric constant and polarity of the solvent influence the stability of transition states during degradation reactions.
• Ionic Strength: Changes in the concentration of electrolytes can affect the reaction rate, particularly for reactions involving charged species.
• Presence of Impurities/Catalysts: Trace metals (e.g., copper, iron) or impurities from excipients can act as catalysts for oxidation or hydrolysis, significantly accelerating degradation.
• Drug-Excipient Interactions: Chemical incompatibility between the drug and excipients (e.g., binders, lubricants) can lead to the formation of degradation products through direct chemical reaction.