**2.2 Composition of transdermal drug delivery systems**

Although transdermal systems can be design as different type systems mentioned above, following are the basic components which generally are used in the formulations of almost all type of transdermal patches (Williams, 2003).


b. **Matrix Systems:** In this type of systems, the drug is dispersed homogeneously within a polymer matrix which has hydrophilic or lipophilic character. Outer side of the formulation is covered with a backing layer. In these systems, patch is held on the skin with a adhesive polymer as a strip. Matrix type formulations can also be prepared by dispersing the drug in an adhesive polymer that is sensitive to direct pressure and then covering this system with an impermeable backing layer. Since in matrix type formulations, release from semi-solid matrix of the drug is not controlled by any membrane, drug release from these systems is related to the surface area to which the patch is applied (Delgado-Charro & Guy 2001; Padula et.al. 2007; Williams, 2003). Minitran (Nitroglycerin), Emsam (Selegeline), Exelon (Rivastigmine), Sancuso (Granisetron) and Oxytrol (Oxybutyne) can be given as examples to commercially available matrix

c. **Adhesive Systems:** In these systems, drug reservoir is prepared by dispersing the drug in an adhesive polymer. At the outmost, an impermeable backing layer takes place. Under the drug reservoir layer, there exists an adhesive membrane controlling the drug release rate. In this type of transdermal systems, drug release rate is controlled both by the matrix in which the drug is dispersed and also by a membrane. Although this type of systems can be designed with a single drug layer, they can be also designed as multi-

Nitrodur (Nitroglycerin), Daytarana (Methyl phenidate) and Duragesic (fentanyl) can be

Although transdermal systems can be design as different type systems mentioned above, following are the basic components which generally are used in the formulations of almost

a. **Drug:** The drug, of which transdermal system will be designed, should possess some physicochemical characteristics. Drug should have relatively low molecular weight (<500 Dalton), medium level lipophilic character (log P 1-3.5) and water solubility (>100 mcg/ml). Also, the drug should be a potent compound, which is effective at low dose

b. **Matrix:** In the formulation of matrix type transdermal systems, the drug is dispersed or dissolved in a polymer matrix (Delgado-Charro & Guy 2001; Williams 2003). This matrix with polymer structure controls the release rate of the drug. Natural (e.g. pectin,

layered (Delgado-Charro & Guy 2001; Padula et.al. 2007; Williams, 2003).

given as examples to commercially available adhesive systems.

**2.2 Composition of transdermal drug delivery systems** 

all type of transdermal patches (Williams, 2003).

Semi-permeable (release) membrane

Solvents, penetration enhancers

(<20 mg) (Guy 1996; Quan 2010).

diffusion controlled systems.

 Drug Matrix Reservoir

 Adhesive Backing layer Release liner

Plasticizers

sodium alginate, chitosan), synthetic (Eudragit, polyvinyl pyrolidon, PVA) and semisynthetic polymers (e.g. cellulose derivatives) are used as polymer (Amnuaikit et al., 2005; Güngör et al., 2008; Lin et al., 1991; Nicoli et al., 2006; Schroeder et al., 2007,a).

