Why does aspirin dissolve faster in warm water? Why does blood maintain its pH at 7.4 despite the acids produced by metabolism? Why do some drugs bind so strongly to plasma proteins that they need higher doses to be effective? The answers come from Physical Pharmaceutics I (PP-I) — the B Pharma 3rd semester subject that applies physical chemistry principles to pharmaceutical systems. From solubility and surface phenomena to complexation and buffer systems, PP I explains the “physics” behind how drugs and formulations behave.
These Physical Pharmaceutics I notes are prepared as per the PCI-approved B Pharma 3rd semester syllabus 2025–26, structured unit-wise from drug solubility and states of matter through surface phenomena, drug-protein complexation, and pharmaceutical buffers. Each unit has a topic summary before the PDF download. PP I carries consistent GPAT weightage — solubility parameters, Raoult’s law, HLB scale, Henderson-Hasselbalch equation, buffer capacity calculations, and distribution law applications are tested regularly.
Download Physical Pharmaceutics I Notes PDF – Unit Wise
Click on the download buttons below to get the PDF notes for each unit. All files are safe and free to download.
Course Units
Unit 1: Solubility of Drugs
Topics Covered: solubility expressions, solute–solvent interactions, solubility parameters, diffusion principles, gas and liquid solubility, Raoult’s law, partially miscible liquids, critical solution temperature, and distribution law with pharmaceutical applications.
Unit 2: States and Physicochemical Properties of Matter
Topics Covered: Explains different states of matter, phase changes, eutectic mixtures, gases and aerosols, crystalline and amorphous solids, and key physicochemical properties like refractive index, optical rotation, dielectric constant, dipole moment, and dissociation constant.
Unit 3: Surface and Interfacial Phenomena
Topics Covered: Discusses surface and interfacial tension, surface free energy, adsorption, spreading coefficient, surface-active agents, HLB scale, solubilization, detergency, and adsorption at solid and liquid interfaces.
Unit 4: Complexation and Protein Binding
Topics Covered: Describes types and analysis of complexation, drug–protein binding, crystalline complex structures, thermodynamic stability, and the role of complexation in drug action.
Unit 5: pH, Buffers and Isotonic Solutions
Topics Covered: Focuses on pH measurement, buffer equations and capacity, buffer applications in pharmaceutical and biological systems, and preparation of buffered isotonic solutions.
What is Physical Pharmaceutics I?
Physical Pharmaceutics-I deals with the physical and chemical principles that govern the behavior of pharmaceutical systems. It helps students understand how drugs and dosage forms interact with physical environments and how these principles influence formulation, stability, and drug performance.
These notes will help you understand topics like:
Matter, Properties, and States: Intermolecular forces, state of matter, and phase transitions
Micromeritics: Particle size, shape, surface area, porosity, and their measurement methods
Rheology: Flow properties of liquids and semisolids, Newtonian and non-Newtonian behavior
Surface and Interfacial Phenomena: Surface tension, adsorption, wetting, and surfactants
Complexation and Protein Binding: Types of complexes, stability constants, and biological significance
Buffer Solutions: pH, buffer capacity, preparation, and pharmaceutical importance
Solubility and Distribution Phenomena: Factors affecting solubility, partition coefficient, and applications
Thermodynamics in Pharmacy: Energy, work, enthalpy, and free energy concepts relevant to drug stability
Frequently Asked Questions (FAQ)
Q1. What is the difference between Physical Pharmaceutics I and II?
PP I (3rd semester) covers solubility, states of matter, surface phenomena, complexation, and buffer systems. PP II (4th semester) covers colloidal dispersions, rheology, coarse dispersions (suspensions and emulsions), micromeritics (particle science), and drug stability kinetics. Together they cover the complete physical pharmaceutics syllabus across two semesters.
Q2. What is the HLB scale in pharmacy?
The Hydrophilic-Lipophilic Balance (HLB) scale (0–20) indicates the relative affinity of a surfactant for water vs oil. Low HLB (3–6) = lipophilic surfactants → used for water-in-oil emulsions. High HLB (8–18) = hydrophilic surfactants → used for oil-in-water emulsions. HLB 7–9 = wetting agents. The HLB system helps formulators select appropriate emulsifying agents for specific dosage forms. Covered in Unit 3.
Q3. What is the Henderson-Hasselbalch equation?
The Henderson-Hasselbalch equation describes the relationship between pH, pKa, and the ratio of conjugate base to acid in a buffer solution: pH = pKa + log([A-]/[HA]). It is used to calculate the pH of buffer solutions and to determine the degree of ionisation of weak acids and bases at a given pH — which directly affects drug absorption (since only unionised drugs typically cross biological membranes). Covered in Unit 5.
Q4. What is the distribution law and why is it important in pharmacy?
The distribution (partition) law states that when a solute distributes between two immiscible solvents at equilibrium, the ratio of its concentrations in the two solvents (partition coefficient, K) is constant at a given temperature. In pharmacy, the partition coefficient (log P) determines a drug’s lipophilicity — affecting its absorption, distribution, and formulation. It is used in liquid-liquid extraction of drugs and in the design of controlled-release formulations. Covered in Unit 1.