Chapter 1 Introduction
Development, optimization and evaluation of ofloxacin emulsion based gel for topical drug delivery system 1
1. INTRODUCTION
1.1 Topical preparations
Formulations that are applied to the skin or to mucus membranes are referred to as topical. Drugs administered through the topical route may have both local and systemic effects, depending on where the application is made and on how the formulation is constructed. Three different functions may be achieved when applying formulations to the human skin. Firstly, it may be desirable to have the active remaining on the surface of the skin, e.g. for skin disinfection, dermal insect repellents and cosmetics for skin decoration. These pharmaceuticals or cosmetics are called epidermal…show more content… Structure of human skin
Figure 1.1: Structure of human skin3
The skin is the largest organ of the body with an area of approximately 2m2 and is the interface between the organism and its environment. It prevents the loss of water and the ingress of foreign materials. In essence, the skin consists of three functional layers: the epidermis, the dermis (corneum) and the hypodermis. The hypodermis is a subcutaneous tissue consisting of fat and muscle and acts as a heat isolator, a shock absorber, and an energy storage region. The dermis is 2 mm thick and contains collagen, elastic fibers, blood vessels, nerves as well as hair follicles and sebaceous and sweat glands (figure 1.1). The main cells in the dermis are fibroblasts, which are involved in the immune and inflammatory response and upon which glucocorticoid receptors are found. The dermis is the source of nutrients for the epidermis. Because the epidermis is avascular, essential substances are transported only by passive…show more content… The skin's pH can affect the amount of unionized drug available for skin penetration9. 5. Hydration of skin
It is the most common factor that affects the drug transport across the skin. When water
Chapter 1 Introduction
Development, optimization and evaluation of ofloxacin emulsion based gel for topical drug delivery system 5 enters the skin, tissue softens swells and wrinkles. These events are likely to increase the skin permeation of drug8.
6. Inflammation of skin
Scarred skin in comparison to normal skin will be with no hair follicles and sebaceous glands, thus the penetration is more in injured or abraded skin 9.
Physiochemical Factors 10
1. Partition coefficient
Drug should have some lipid solubility for absorption but at the same time, it should be hydrophilic to diffuse through skin. Thus drug should have optimum partition coefficient.
2. Molecular weight (<400 Dalton)
It is generally believed that larger the molecular weight slower is the drug permeation through skin as larger molecules diffuse slowly through skin because of their large molecular volume.
3. Degree of ionization (only unionized drugs gets absorbed