Physical Pharmaceuticals 1 - Unit 1

Introduction

• Covers entire Unit 1 of Physical Pharmaceuticals for B Pharmacy 3rd Semester.
• Focus on important topics: Rauts Law, Solubility of Drug, and Distribution Law.

Solubility of Drug

Definition

• Solubility: Maximum amount of solute that can be dissolved in 100 ml of solvent at constant temperature and pressure.
• Solvent: Substance in larger amount; Solute: Substance in lesser amount.
• Example: Sugar dissolving in milk.

Types of Solutions

• Saturated Solution: Contains maximum solute at constant temperature.
• Unsaturated Solution: Can dissolve more solute.
• Super Saturated Solution: Dissolves more solute than normal capacity.

Solubility Expression

• Very soluble, Freely soluble, Soluble, Sparingly soluble, Slightly soluble, Very slightly soluble, Practically insoluble.
• Based on the parts of solvent needed to dissolve one part of solute.

Mechanism of Solute-Solvent Interaction

Steps

1. Detachment of Solute: Solute molecules detach from the bulk.
2. Formation of Vacant Site in Solvent: Solvent creates space for solute.
3. Insertion of Solute: Solute fits into the solvent's vacant sites.

Solvation

• Solute molecules surrounded by solvent, forming a solvation complex.

Factors Affecting Solubility

General Factors

1. Temperature: Directly proportional to solubility.
2. pH: Affects ionizable drugs; requires optimum pH.
3. Pressure: Affects gases more than solids or liquids.
4. Particle Size: Smaller particles increase surface area and solubility.
5. Solvent Polarity: Like dissolves like principle.
6. Molecular Weight: Larger molecular weight generally decreases solubility.

Important Questions and Concepts

Distribution Law

• Understands solute distribution between two immiscible solvents.
• Determines hydrophilic or lipophilic nature of the solute.

Rauts Law

• Vapor pressure of a solution is directly proportional to the mole fraction of the solvent.
• Describes ideal solutions and non-ideal solutions.

Diffusion Principle in Biological Systems

• Movement from high to low concentration without energy.
• Important for drug distribution in the body.

Conclusion

• Covered solubility, diffusion, and Rauts Law in detail.
• Essential for understanding drug formulation and delivery.