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TRANSDERMAL PATCHES


About Authors: 
Shakya Pragati*
, Khwaja Sadiya,
Asst. Professor, Integral University,
Lucknow,
U.P, India

1.ABSTRACT
Transdermal delivery of medications was foreshadowed in earlier eras by the use of certain plasters and ointments. The mustard plaster, applied as a home remedy for severe chest congestion, may be considered an example. (This author remembers his mother making mustard plasters for members of the family.) Powdered mustard seed (Brassica nigra) was mixed with warm water, and the resulting paste was spread on a strip of flannel, which was applied to the patient’s chest with a cloth binding wrapped around the body to hold the plaster in place. The moisture and body warmth activated an enzyme (myrosin) in the mustard that hydrolyzed a glycoside (sinigrin), causing the release of the pungent active ingredient allyl isothio-cyanate (CH2=CHCH2NCS) (7). This substance possesses the qualifications listed above for transdermal absorption. A transdermal patch or skin patch is a medicated adhesive patch that is placed on the skin to deliver a specific dose of medication through the skin and into the bloodstream.

Reference Id: PHARMATUTOR-ART-1235

There are four types of transdermal drug delivery system: 
1. Membrane permeation Controlled systems  
2. Matrix diffusion-controlled system 
3. Adhesive dispersion- type system
4. Microreservoir type or microsealed dissolution controlled systems.

The basic components of transdermal patches are Polymer matrix or matrices , drug , Permeation enhancers and  other excipients. The mechanism of permeation can involve the passage through the epidermis itself known as transepidermal absorption. Transderm-Scop , Nitro dur ,Transderm-Nitro are some of the marketed formulations of transdermal patches.

2. INTRODUCTION
Transdermal drug delivery system has been in existence for a long time. In the past, the most commonly applied systems were topically applied creams and ointments for dermatological disorders.The occurrence of systemic side-effects with some of these formulations is indicative of absorption through the skin. A number of drugs have been applied to the skin for systemic treatment. In a broad sense, the term transdermal delivery system includes all topically administered drug formulations intended to deliver the active ingredient into the general circulation. Transdermal therapeutic systems have been designed to provide controlled continuous delivery of drugs via the skin to the systemic circulation. Moreover, it over comes various side effects like painful delivery of the drugs and the first pass metabolism of the drug occurred by other means of drug delivery systems. So, this Transdermal Drug Delivery System has been a great field of interest in the recent time. Many drugs which can be injected directly into the blood stream via skin have been formulated. The main advantages of this system are that there is controlled release of the drug and the medication is painless.  The drug is mainly delivered to the skin with the help of a transdermal patch which adheres to the skin. A Transdermal Patch has several components like liners, adherents, drug reservoirs, drug release membrane etc. which play a vital role in the release of the drug via skin. Various types of patches along with various methods of applications have been discovered to delivery the drug from the transdermal patch. Because of its great advantages, it has become one of the highly research field among the various drug delivery system. Here, a general view over the transdermal patch has been discussed along with its advantages, disadvantages, methods of applying, care taken while applying, types and applications of transdermal patch and recent advances along with recent patents and market products.

Definition:
A transdermal patch or skin patch is a medicated adhesive patch that is placed on the skin to deliver a specific dose of medication through the skin and into the bloodstream.
The first commercially available prescription patch was approved by the United States Food and Drug Administration in December 1979, which administered scopolamine for motion sickness.
Transdermal drug delivery system are topicaly administered medicaments in the form of patches that deliver drugs for systemic effects at a predetermined and controlled rate. A transdermal drug delivery device, which may be of an active or a passive design, is a device which provides an alternative route for administering medication. These devices allow for pharmaceuticals to be delivered across the skin barrier. In theory, transdermal patches work very simply.  A drug is applied in a relatively high dosage to the inside of a patch, which is worn on the skin for an extended period of time.  Through a diffusion process, the drug enters the bloodstream directly through the skin.  Since there is high concentration on the patch and low concentration in the blood, the drug will keep diffusing into the blood for a long period of time, maintaining the constant concentration of drug in the blood flow.
This approach to drug delivery offers many advantages over traditional methods. As a substitute for the oral route, transdermal drug delivery enables the avoidance of gastrointestinal absorption, with its associated pitfalls of enzymatic and pH associated deactivation. This method also allows for reduced pharmacological dosaging due to the shortened metabolization pathway of the transdermal route versus the gastrointestinal pathway. The patch also permits constant dosing rather than the peaks and valleys in medication level associated with orally administered medications. Multi-day therapy with a single application, rapid notification of medication in the event of emergency, as well as the capacity to terminate drug effects rapidly via patch removal, are all further advantages of this route. 

However this system has its own limitations in which the drug that require high blood levels cannot be administered and may even cause irritation or sensitization of the skin.the adhesives may not adhere well to all types of skin and may be uncomfortable to wear. Along with these limitations the high cost of the product is also a major drawback for the wide acceptance of this product. (5)

3.TYPES OF TRANSDERMAL DRUG DELIVERY SYSTEMS

3.1 Membrane permeation Controlled systems:
In this type of system,the drug reservoir is totally encapsulated in a shallow compartment moulded from a drug impermeable metallic plastic laminate and a rate controlling polymeric membrane e.g. Ethylene vinyl acetate with defined drug permeability. The drug molecules are permitted to release only through the rate-controlling membrane. In         the drug reservoir compartment ,the drug solids are either dispersed in a solid-polymer matrix or suspended in a viscous liquid medium to form a paste like suspension.A thin layer of adhesive polymer is applied to the external surface of the rate-controlling membrane to achive an intimate contact of the transdermal system and the skin surface.

Example: Transderm-Nitro , Transderm-Scop , Catapress , Estraderm .(4)

3.2 Matrix diffusion-controlled system:
In this approach, the drug reservoir is prepared by homogenously dispersing drug particles in a hydrophilic or lipophilic polymer matrix.The resultant medicated polymer is then moulded into a medicated disc with a defined surface area and controlled thickness.This drug reservoir containing polymer disc is then pasted on to an occlusive base plate in a compartment fabricated from a drug impermeable plastic backing. The adhesive polymer is then spread along the circumference to form a strip of adhesive rim  around the medicated disc.(4)

Example: Nitro-Dur System .

 3.3 Adhesive dispersion- type system:
This is a simplified form of the membrane permeation-controlled system . The drug reservoir is formulated by directly dispersing the drug in an adhesive polymer eg. polyisobutylene and then spreading  the medicated adhesive , by solvent casting or hot melt  onto a flat sheet of drug impermeable metallic plastic backing to form a thin drug reservoir layer. On the top of the drug reservoir layer, thin layers of non- medicated, rate-controlling adhesive polymer of a specific permeability are applied to produce an adhesive diffusion - controlled delivery system.

Example: Deponit , Frandol Tape . (4)

3.4 Microreservoir type or microsealed dissolution controlled systems:
Here, the drug reservoir is formed by first suspending the drug solids in an aqueous solution of a water soluble liquid polymer and then dispersing the drug suspension homogenously in a lipophilic polymer by high shear mechanical force to form a large number  of microreservoirs. These are unleachable microscopic spheres of drug reservoirs . This thermodynamically unstable dispersion is  stabilized quickly by immediate addition of cross linking polymers like Gluteraldehyde the polymer which produces a medicated polmer disc with a constant surface area  and a fixed thickness. A transdermal therapeutic system is produced by positioning the medicated disc at the centre and     surrounding it with an adhesive rim and then it is spread on to the occlusive base plate with adhesive foam pad.

Example: Nitro-Disc System . (4)

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