Types Of Transdermal Drug Delivery System And Transdermal Patches

Transdermal drug delivery (TDD) systems are designed to deliver biologically active agents (drugs or cosmeceuticals) through the skin, principally by diffusion, for local internal if not systemic effects. TDD is defined as self-contained, discrete dosage forms which, when applied to the intact skin, deliver the drug, through the skin at controlled rate to the systemic circulation.

Transdermal patch

TDDS can offer a controlled release of the drugs through the skin into the patients, which could reduce the first-pass metabolism effects, lessen systemic side effects, improve the dosage efficacy by enabling steadier blood drug profiles throughout the treatment, and enhance patient compliance.

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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 mechanism of permeation can involve the passage through the epidermis itself known as transepidermal absorption.

Type Of Transdermal Drug Delivery System

There are four types of transdermal drug delivery system;

1. Membrane permeation Controlled systems: 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 achieve an intimate contact of the transdermal system and the skin surface.

2. Matrix diffusion-controlled system: the drug reservoir is prepared by homogeneously 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 disk.

3. Adhesive dispersion- type 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.

4. Micro Reservoir type or micro sealed 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 homogeneously in a lipophilic polymer by high shear mechanical force to form a large number of micro reservoirs. These are unreachable microscopic spheres of drug reservoirs. This thermodynamically unstable dispersion is stabilized quickly by immediate addition of cross linking polymers like glutaraldehyde, the polymer which produces a medicated polymer 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.

Types Of Pharmaceutical Transdermal Delivery Patch

There are five main types of transdermal patches;

Single-layer Drug-in-Adhesive

Comes with a liner, backing and an adhesive. The adhesive holds the whole system together along with the drug.

Multi-layer Drug-in-Adhesive

Very similar to the first. The only difference is the presence of another layer of drug-in-adhesive. This may be separated by a membrane.

Reservoir

The reservoir is a separate drug layer totally encapsulated in a shallow compartment molded from a drug-impermeable metallic plastic laminate, with a rate-controlling membrane made of a polymer. This reservoir is a liquid compartment for suspension or solution. It consists of all other layers in the second type and it's a drug that obeys the first order.

Vapour Patch

In a vapour patch, the adhesive layer not only serves to adhere the various layers together but also to release vapour. Vapour patches release essential oils for up to 6 hours and are mainly used for decongestion.

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Matrix

The matrix system has a drug layer of a semisolid matrix containing a drug solution or suspension. The adhesive layer in this patch surrounds the drug layer, partially overlapping it. Also known as a monolithic device.

Components Of Transdermal Patches

The basic components of transdermal patches are polymer matrix or matrices, drug, permeation enhancers and other excipients.

Function Of Components Of Transdermal Patches

Description of the components to a transdermal patch are:

Liner

This is a piece of protector that is remove prior to use

Drug

The drug that is released on exposure to the skin after the liner is removed.

Physicochemical Properties Of Drug

1. The drug should have a molecular weight less than approximately 1000 daltons

2. The drug should have affinity for both – lipophilic and hydrophilic phases. Extreme partitioning characteristics are not conducive to successful drug delivery via the skin.

3. The drug should have a low melting point.

4. Along with these properties the drug should be potent, have a short half life and be non irritating

Adhesive

Dual purpose of adhering the whole components together and to the skin.

Both adhesive systems should fulfill the following criteria;

(i) Should adhere to the skin aggressively, and should be easily removed.

(ii) Should not leave a non washable residue on the skin.

(iii) Should not irritate or sensitize the skin

The face adhesive system should also fulfill the following criteria;

(i) Physical and chemical compatibility with the drug, excipients and enhancers of the device of which it is a part

(ii) Permeation of drugs should not be affected

(iii) The delivery of simple or blended permeation enhancers should not be affected e.g. polyisobutylene, acrylics and silicones

Polymer Matrix (Membrane)

Controls the release of the drug from the reservoir and multi-layer patches. Example are:

a) Natural Polymers: they include cellulose derivatives, zein, gelatin, shellac, waxes, proteins, gums and their derivatives, natural rubber and starch

b) Synthetic Elastomers: they include polybutadiene, hydrin rubber, polysiloxane, silicone rubber, nitrile, acrylonitrile, butyl rubber, styrene butadiene rubber, neoprene, etc.

c) Synthetic Polymers: e.g. polyvinyl alcohol, polyvinyl chloride, polyethylene, polypropylene, polyacrylate, polyamide, polyurea, polyvinylpyrrolidone, polymethylmethacrylate, epoxy, etc.

Backing

They are flexible and protect the patch from the outer environment and accept printing e.g metallic plastic laminate, etc.

Permeation Enhancer

These are permeation promoters for drugs, which increase delivery of drugs by increasing skin permeability. These may conveniently be classified under the following main headings;

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a) Solvents: These compounds increase penetration possibly by swallowing the polar pathway and/or by fluidizing lipids. Examples include water alcohols – methanol and ethanol; alkyl methyl sulfoxides – dimethyl sulfoxide, etc, miscellaneous solvents – propylene glycol, glycerol, etc.

b) Surfactants: These compounds are proposed to enhance polar pathway transport, especially of hydrophilic drugs.The ability of a surfactant to alter penetration is a function of the polar head group and the hydrocarbon chain length.

i. Anionic Surfactants: e.g. dioctyl sulfosuccinate, Sodium lauryl sulphate, etc

ii. Nonionic Surfactants: e.g. pluronic F127

iii. Bile Salts: e.g. sodium ms taurocholate, etc

iv. Binary system: These systems apparently open up the heterogeneous multilaminate pathway as well as the continuous pathways e.g. propylene glycol-oleic acid and 1, 4-butanediol-linoleic acid.

c) Miscellaneous chemicals: These include urea, a hydrating and keratolytic agent; N, N-dimethyl-m-toluamide; calcium thioglycolate; anticholinergic agents.

Matrix Filler

Provides bulk to the matrix, and some act as matrix stiffening agents.

Drug Reservoir

Purse that house the drug

Other components include: stabilizer (antioxidants), preservatives etc.