B Pharmacy

Mechanism of Hydrolysis: Hydrolysis involves nucleophilic attack of water on labile functional groups, breaking chemical bonds such as esters and amides. Example: $\mathrm{R{-}COOR’} + H_{2}O \;\longrightarrow\; \mathrm{R{-}COOH} + \mathrm{R’OH}$ Commonly Affected Drug Classes: Esters: aspirin, procaine Amides: lidocaine, procainamide Lactams: penicillins, cephalosporins Carbamates, imines Stabilization Strategies for Hydrolysis Strategy Explanation pH control (buffering) Adjust formulation … Read more

Specific Acid/Base Catalysis: Catalysis by hydronium (H₃O⁺) or hydroxide (OH⁻) only. Rate is pH-dependent. Rate law: \(\text{Rate} = k_H [H_3O^+] + k_{OH} [OH^-]\) General Acid/Base Catalysis: Catalysis by any proton donor (acid) or proton acceptor (base), e.g., acetate, phosphate, ammonia. Buffers can contribute to catalysis. Rate law (general form): $\text{Rate} = k + k_{AH}[AH] + … Read more

Definition of Dielectric Constant: Dielectric Constant Measure of a solvent’s polarity. High dielectric constant = high polarity (e.g., water = 80). Effect: High ε (e.g., water) stabilizes ionic species and may increase or decrease the rate depending on the mechanism. Solvents with low dielectric constants may: Promote neutral or non-ionic pathways Inhibit ionization-dependent reactions For … Read more

Definition of Ionic Strength: Ionic strength (μ) is a measure of total ion concentration in solution. $\mu = 12 \sum c_i z_i^2$$\mu = \tfrac{1}{2} \sum c_i z_i^2$$\mu = 21 \sum c_i z_i^2$ Where: ci​ = concentration of ion i zi​ = charge of ion i Effect: Reactions involving charged species are influenced by ionic strengths: … Read more

Effect of Solvent: Solvents can change the reaction medium, affecting: Solubility of the drug Polarity of the medium Hydrolysis or oxidation rate Some solvents may stabilize or destabilize the drug. Co-solvent Systems: Adding solvents like ethanol can: Change solvation Affect reaction kinetics Modify degradation pathways Examples: Hydrolysis is faster in aqueous solutions. Adding organic solvents … Read more

Effect of Temperature: As Temperature increases, the rate of degradation increases. Described by Arrhenius equation: $k = A \cdot e^{-\tfrac{E_a}{RT}}$ Where: k = rate constant A = frequency factor Ea​ = activation energy (J/mol or cal/mol) R = gas constant (8.314 J/mol·K or 1.987 cal/mol·K) T = temperature in Kelvin Implications: Helps estimate shelf life … Read more