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Renin Angiotensin Mechanism.

Basic Components of TDDS.

 

  • A typical Transdermal drug delivery system consists of the following components.

    • Polymer Matrix.

    • Drugs.

    • Permeation Enhancers.

    • Pressure sensitive adhesives (PSA).

    • Backings Laminates.

    • Release Liner.

    • Other Excipients.

  1. Polymer Matrix:

  • The Polymer controls the release of the drug from the device. 

  • Possible useful polymers for transdermal devices are: 

  •  a. Natural Polymers: 

    • cellulose derivatives, 

    • Zein, 

    • Gelatin, 

    • Shellac, 

    • Waxes, 

    • Proteins, 

  • Gums and their derivatives, 

    • Natural rubber, 

    • Starch etc. 

  •  b. Synthetic Elastomers: 

    • polybutadiene, 

    • Hydrin rubber, 

    • Polysiloxane, 

    • Silicone rubber, 

    •  Nitrile, 

    • Acrylonitrile, 

    • Butyl rubber, 

    • Styrene Butadiene rubber, 

    • Neoprene etc. 

  •  c. Synthetic Polymers: 

    • polyvinyl alcohol, 

    • Polyvinyl chloride, 

    • Polyethylene, 

    • Polypropylene, 

    • Polyacrylate, 

    • Polyamide, 

    • Polyurea, 

    • Polyvinyl pyrrolidone, 

    • Polymethyl methacrylate, 

    • Epoxy etc.

  1. Drugs:

  • Desirable properties of a drug for transdermal delivery. 

    • The drug should have a molecular weight of less than 1000 Daltons. 

    • The drug should have affinity for both lipophilic and hydrophilic phases. 

    • Extreme partitioning characteristics are not useful for successful drug delivery via the skin. 

    • The drug should have a low melting point. 

    • Drug should be potent, have a short half life and be non irritating. 

  1. Permeation Enhancers:

  • These are compounds that promote skin permeability by altering the skin as a barrier to the flux of a desired penetrant. 

  • Penetration enhancers are added to a formulation to improve the diffusivity and solubility of drugs through the skin, thereby reducing the skin's barrier resistance. 

  • These includes water,pyrrolidones,fatty acids and alcohols, alcohol and glycols, essential oils,terpenes and derivatives,sulfoxides like DMSO and their derivatives, urea and surfactant. 

  1. Pressure sensitive adhesives (PSA):

  • The fastening of all transdermal devices to the skin can be done by using a PSA.

  • The first approach involves the development of new polymers, which include hydrogel hydrophilic polymers, and polyurethanes. 

  • The second approach is to physically or chemically modify the chemistries of the PSAs in current use (such as silicones, and acrylates). 

  • Physical modification refers to the formulation of the base adhesives with some unique additives so that there is enhanced drug delivery and improved skin-adhesion properties. 

  • Chemical modification involves chemically incorporating or grafting functional monomers to the conventional PSA polymers in order to improve drug delivery rates 

  1. Backings Laminates:

  • Backings laminates are selected for appearance, flexibility and need for occlusion. 

  • Examples of backings are polyester film, polyethylene film and polyolefin film, and aluminium vapour coated layer. 

  • Major areas of concern are the backing additives leaching out and diffusion of drugs or the compositions, through the backing. 

  • An over emphasis on the chemical resistance often may lead to stiffness and high occlusivity to moisture vapour and air. 

  • It causes the TDDS to lift and may possibly irritate the skin during long-term use. 

  1. Release Liner: 

  • During storage, the patch is protected by a liner, which is removed and discarded before the patch is applied to the skin. 

  • Since the liner is in direct contact with the TDDS, the liner must be chemically inert. 

  • The release liner is composed of a base layer which may be non-occlusive (e.g. paper fabric) or occlusive (e.g. polyethylene, polyvinyl chloride) and a release coating layer made up of silicon or Teflon. 

  • Other materials used for TDDS liners include, polyester foil and metalized laminate that protects the patch during storage. 

  • The liner is removed prior to use only.

  1. Other Excipients:

  • Various solvents such as chloroform, methanol, acetone, isopropanol and dichloromethane are used to prepare drug reservoirs. 

  • In addition, plasticizers such as dibutyl-phthalate, triethyl citrate, polyethylene glycol and propylene glycol are added to provide plasticity to the transdermal patch. 

Commonly asked questions.

  1. Write in brief about the basic components of a TDDS.
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