About Physical Pharmaceutics I
Subject Code
BP302T
Semester
Semester 3
Credits
4 Credits
Physical Pharmaceutics I (BP302T) is the science of how physicochemical properties affect drug behavior. You will study why drugs dissolve (Solubility), how surfaces interact (Surface Tension), how drugs bind to proteins, and how pH is controlled (Buffers). These concepts directly translate to designing stable and effective drug formulations.
Key Learning Objectives
- Explain Solubility: Describe the key factors affecting the solubility of drugs and how they can be improved.
- Apply Raoult’s Law: Calculate vapour pressure of solutions and explain deviations.
- Understand Surface Tension: Explain how surfactants (HLB scale) are selected for formulations.
- Explain Complexation: Describe how drug complexation affects bioavailability.
- Calculate Buffer Capacity: Apply the Henderson-Hasselbalch equation to solve buffer problems.
Syllabus & Topics Covered
Unit 1: Solubility of Drugs
- Solubility expressions: percentage, molarity, molality, mole fraction.
- Mechanisms of solute-solvent interactions; ideal solubility parameters; solvation and association.
- Quantitative approach to factors influencing solubility (temperature, pH, cosolvent, particle size).
- Diffusion principles in biological systems (Fick’s laws).
- Solubility of gases in liquids (Henry’s law).
- Solubility of liquids in liquids: Binary solutions, ideal solutions, Raoult’s law, real solutions.
- Partially miscible liquids, Critical Solution Temperature (CST) and applications.
- Distribution law (Partition coefficient), its limitations and applications.
Unit 2: States of Matter & Physicochemical Properties
- States of matter: changes, latent heats, vapour pressure, sublimation, critical point, eutectic mixtures.
- Gases, Aerosols and inhalers, relative humidity.
- Liquid complexes, liquid crystals, glassy states, solid crystalline, amorphous, and polymorphism.
- Physicochemical Properties of Drug Molecules: Refractive index and optical rotation.
- Dielectric constant, dipole moment, dissociation constant – determinations and applications.
Unit 3: Surface and Interfacial Phenomenon
- Liquid interface, surface and interfacial tensions, surface free energy.
- Measurement of surface and interfacial tensions (capillary rise, stalagmometer).
- Spreading coefficient, adsorption at liquid interfaces.
- Surface active agents (Surfactants): Classification.
- HLB Scale: Concept, determination, and application in formulation selection.
- Solubilisation, detergency.
- Adsorption at solid interface (Freundlich and Langmuir isotherms).
Unit 4: Complexation and Protein Binding
- Introduction to Complexation, classification of complexes.
- Applications of complexation in pharmacy.
- Methods of analysis of complexes.
- Protein binding: drug-protein binding equilibrium.
- Complexation and drug action.
- Crystalline structures of complexes.
- Thermodynamic treatment of stability constants.
Unit 5: pH, Buffers and Isotonic Solutions
- Sorensen’s pH Scale and its significance.
- pH determination: electrometric (using pH meter) and colorimetric methods.
- Applications of buffers in pharmaceutical formulations.
- Buffer equation (Henderson-Hasselbalch equation): derivation and applications.
- Buffer capacity: definition, calculation, and significance.
- Buffers in pharmaceutical and biological systems.
- Buffered isotonic solutions: concept of isotonicity.
How to Score High in Physical Pharmaceutics I
- 1
Henderson-Hasselbalch Equation: Memorize and practice pH = pKa + log([A-]/[HA]). You will use this in both theory and calculations.
- 2
HLB Scale Application: For emulsions, O/W needs HLB 8-18; W/O needs HLB 3-6. This is a common MCQ topic.
- 3
Raoult’s Law Calculations: Practice numerical problems on vapour pressure lowering and ideal solutions.
- 4
Distribution Law Applications: Understand how partition coefficient relates to drug absorption and extraction.
- 5
Polymorphism Importance: Know why different polymorphic forms of a drug can have different solubility and bioavailability (e.g., Chloramphenicol palmitate).
Why it Matters for Career
Physical Pharmaceutics is the science behind formulation design. Every tablet, capsule, injection, and cream you formulate requires knowledge of solubility, buffers, surface tension, and stability. This subject is fundamental for careers in Formulation R&D and Quality Control.
Exam Weightage
Unit 5 (pH/Buffers – Henderson-Hasselbalch calculations) and Unit 1 (Solubility, Raoult’s law) are high-scoring and calculation-based. Unit 3 (HLB Scale, Surface Tension) is a sure-shot question. Don’t neglect Unit 4 (Complexation) for long-answer questions.
Frequently Asked Questions (FAQs)
What is the Henderson-Hasselbalch equation?
pH = pKa + log([A⁻]/[HA]) for an acid buffer. It relates the pH of a buffer to the pKa of the weak acid and the ratio of the concentrations of the conjugate base and weak acid.
What is the HLB Scale?
Hydrophilic-Lipophilic Balance (HLB) is a numerical scale (0-20) for classifying surfactants. Low HLB (3-6): W/O emulsifiers. High HLB (8-18): O/W emulsifiers. HLB 7-9: Wetting agents.
What is Critical Solution Temperature?
The temperature at which two partially miscible liquids become completely miscible (UCST) or completely immiscible (LCST). For phenol-water, the UCST is 65.6°C. CST is used in quality control.
What is Polymorphism in pharmacy?
Polymorphism is the ability of a solid to exist in two or more crystalline forms with different internal structures. Different polymorphs have different melting points, solubility, and bioavailability (e.g., Form I vs Form II of Carbamazepine).
What is Buffer Capacity?
Buffer capacity (β) is the number of moles of strong acid or base needed to change the pH of 1 litre of buffer by 1 unit. Maximum buffer capacity occurs when pH = pKa (equal amounts of acid and conjugate base).