Introduction to Semisolid Dosage Forms
Unit 5 covers the formulations we apply on our skin—Creams, Ointments, Gels, and Pastes. You will learn the science of how drugs penetrate the skin barriers and the excipients used to make these semisolids stable and effective. It also covers the evaluation tests (like Spreadability, pH, Viscosity) used to ensure the quality of these products.
Syllabus & Topics
- 1Semisolid Dosage Forms: Definition, Classification
- 2Mechanisms and Factors Influencing Dermal Penetration
- 3Ointments: Bases, Preparation (Trituration/Fusion), Evaluation
- 4Creams: Types (O/W, W/O), Preparation
- 5Pastes: Definition, Characteristics, Preparation
- 6Gels: Definition, Gelling agents, Preparation
- 7Excipients used in Semisolid Dosage Forms: Preservatives, Antioxidants, Humectants
- 8Evaluation: pH, Spreadability, Extrudability, Viscosity
Learning Objectives
Frequently Asked Questions (FAQs)
Q1. What are Ointments?
Ointments are greasy, semisolid preparations intended for application to the skin or mucous membranes. They usually contain less than 20% water and more than 50% hydrocarbons or waxes.
Q2. How do Creams differ from Ointments?
Creams are semisolid emulsions of oil and water. They are less greasy, more spreadable, and easily washable with water compared to ointments, which are oily and form an occlusive film on the skin.
Q3. What are Gels?
Gels (jellies) are transparent or translucent semisolid systems consisting of dispersions of small or large molecules in an aqueous liquid vehicle, rendered jelly-like by the addition of a gelling agent such as carbopol.
Q4. What is the role of Penetration Enhancers?
Penetration enhancers (e.g., DMSO, urea) increase the permeability of the skin, especially the stratum corneum, allowing the drug to pass through more easily.
Q5. What are Pastes?
Pastes are ointments containing a high proportion of insoluble solid powders (up to 50%, e.g., zinc oxide). They are stiffer than ointments and are mainly used for their protective and absorptive action.