There are many instance where some drugs are required to be administered to patients in a steady and continuous form usually for longer duration directly in to their systemic circulation, many are benefitted bypassing first pass metabolism, therefore transdermal drug delivery systems have immerged as very useful dosage forms for some patients, life saving drugs like nitroglycerin are available transmucosal and transdermal drug delivery systems.
A typical transdermal drug delivery system (TDDS) consist of drug patches or reservoirs formed with mechanical supports and barriers and support provided by liners and frames, a patch of a drug being delivered is formed which can be applied over skin with a help of suitable adhesive.
As the transdermal drug delivery system (TDDS) consists of both mechanical units and drug reservoir systems formed and controlled with mechanical barriers , they are classified under combination drug products required to comply with all requirements of a combination drug products.
Components of transdermal drug delivery system (TDDS) are as follows:
Drug is loaded in the form of suspension or solution with suitable co-solvents and held in a reservoir held in to a support frame which is then separated and protected from outer environment with a protective liner . Drug blended in to suitable adhesive , or can be formed in to a matrix system as drug releasing matrix.
Help in maintaining the transdermal drug patch intact while in storage from outer environments , the are removed before application transdermal drug delivery system (TDDS) on skin.
Help in fixing drug layers over applied skin surface , drug can also be mixed in the adhesive substance.
4. Drug release enhancers, drug permeation enhancer:
Co solvents like terpins , alcohols surface active agents like sodium lauryl sulfate , and pyrrolidones in varying proportions are used to enhance and control the drug permeation from drug reservoir or drug matrix system.
5. Backing layer: Silicon rubber , cellulose derivatives , Polypropylene is used to protect drug patch environment.
Advantages of transdermal drug delivery system (TDDS)
1.Patients acceptance or compliance for transdermal drug delivery system is good as they do not feel that they are taking drug as in conventional dosage forms as in tablet and injections.
2. Steady and content delivery of a drug can be achieved for a longer duration, without sudden rise and dropdown in plasma concentration of drug.
3. This route of drug administration is further developed in to transmucosal drug delivery systems TMDS, with which a drug can be absorbed as quickly as that of injectable dosage form, maintaining a steady concentration throughout the application even large peptide molecules can be delivered by transmucosal drug delivery system with the help of drug loaded liposome
Disadvantages of transdermal drug delivery system (TDDS):
1. The drug required to be loaded in the transdermal drug delivery system patch and related drug delivery systems is usually very higher than the actual required drug dose to be administered.
2. Accidental exposure of used transdermal drug delivery systems has resulted in to some fatal incidences in children’s and for healthcare professionals.
3. Drug absorption in to skin is a zero order, though drug absorption skin does not depend on the concentration beyond a particular concentration, but it largely depends on the aria of the applied skin and contact time.
Evaluation of transdermal drug delivery system (TDDS):
Following tests are used to evaluate transdermal drug delivery system (TDDS):
Interaction studies carried out and required to be reported to evaluate interactions between drug and adhesives and other components of system which will have its effect on bioavailability of drug in the system up on application.
Thickness of the patch:
Measured at different points on the patch with micrometer, and it is required that the thickness do not vary beyond allowed limit so that a uneven delivery of drug from different point is avoided so that the system remains optimized.
Is found by repeated folding after cutting the patch appropriately and applying repeated folding, this gives an idea how good is the patch to bare and remain intact for folding while in storage and during usage.
Following are some important tests used in evaluation of transdermal drug delivery system.
Percentage Moisture content:
Percentage Moisture uptake
Water vapour permeability (WVP) evaluation
Rolling ball tack test:
Quick Stick (peel-tack) test:
Probe Tack test
In vitro drug release studies
In vitro skin permeation studies
Uniformity of dosage unit test
Shear Adhesion test
Peel Adhesion test
Thumb tack test
Percentage Elongation break test
Skin Irritation study
Good Manufacturing Practices
Liposomal drug delivery system
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