How is HRT administered

There are various ways of administering HRT. Some of them include: oral, parenteral, rectal, vaginal, topical and transdermal (through the skin).  These treatments can also be classified as oral, percutaneous and transdermal.
 

What are transdermal drug delivery systems

Transdermal (through the skin) drug delivery system is one way of administering HRT.  Other methods of administering HRT include oral, parenteral, rectal, vaginal and topical.

Transdermal applicators are the patches containing the drug.  They are flat, smooth, discrete and can be used for long term medication. Transdermal delivery systems are not just an alternative route of administration but they improve the therapeutic value of a drug and provide many other advantages including increasing compliance.

Transdermal therapy could be of two types: (a) Reservoir type: Those that control the rate of drug delivery to skin; and (b) Matrix type: Those that allow the skin to control rate of drug absorption.
 

Why is skin the site for transdermal drug delivery

Skin is one of the most readily accessible organs of the human body. It has a thickness of only a few mm.  Skin is a multi-layered organ composed of many histological layers.  Its three main layers are: the epidermis, the dermis and the hypodermis.

The epidermis is further divided into 5 anatomical layers. The outermost layer is the stratum corneum which is exposed to external environment. The transdermal permeation of neutral molecules at steady state can be considered as a process of passive diffusion through the stratum corneum in the interfollicular region.
 

General considerations for the use of Transdermal Drug Delivery systems 

1. The site selected for application should be clean dry and hairless e.g. estradiol patches are applied to buttocks or abdomen, nitroglycerine patches are applied to chest. Scopolamine behind ear. Because of possible occurrence of skin irritation, sites of application for patches are rotated weekly. 
2. Transdermal patch should not be applied to skin that is already irritated or act so as to ensure maximum absorption. 
3. Patches should be removed from its protective package being careful not to tear or damage patch. Protective backing should be removed to expose the adhesive layer and it should be applied firmly with the palm of the hand until it is secured in place. 
4. Patches may be left on when bathing or swimming. If the patch gets dislodged one must re-apply it or it may be replaced.