Simple Pharmanotes

  TDDS can be formulated by different ways as follows, Polymer membrane permeation controlled TDDS. Polymer matrix diffusion controlled TDDS. Adhesive Dispersion – Type Systems. Microreservoir dissolution controlled TDDS. Polymer membrane permeation controlled TDDS: A polymeric membrane that controls flow rate is positioned between a backing laminate that is drug-impermeable and a drug reservoir .  The drug is evenly distributed throughout the drug reservoir compartment in a solid polymeric matrix (like polyisobutylene) and suspended in a viscous, non-leachable liquid medium (like silicon fluid) to create a paste-like suspension.  A polymeric membrane that controls rate can be either microporous or nonporous, such as ethylene-vinyl acetate copolymer .  Estraderm (used twice weekly to treat postmenopausal syndrome) and Duragesic (used to manage chronic pain for 72 hours) are two examples of this type of patch.  The intrinsic rate of drug release from this type of drug delivery system

  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. 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. Drugs: Desirable properties of a drug for transdermal delivery.  The drug should have a molecular weight of less than 1000 D

  Permeation Enhancers: These substances work to improve skin permeability by altering the ability of a desired penetrant to pass through the skin.   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.   This allows the drug to penetrate to the viable tissues and enter the systemic circulation.   The flux J of drug across the skin can be written as    J = D [dc/dx]  Where, J = The Flux, D = diffusion coefficient,  C = Concentration of the diffusing species,  X = Spatial coordinate.   The methods employed for modifying the barrier properties of the SC to enhance the drug penetration (and absorption) through the skin can be categorised as chemical and physical methods of enhancement .  Chemical Enhancers: Chemical permeation enhancers can work by one or more of the following four principle mechanisms:  Relaxation of the stratum corneum's highly ordered lipid