TRANSDERMAL ROUTE
Highly lipid soluble drugs can be applied over the skin for slow and prolonged absorption, e.g. nitroglycerine ointment in angina pectoris. Adhesive units, inunction, iontophoresis and jet injection are some forms of transdermal drug delivery.
Adhesive units (transdermal therapeutic systems) are adhesive patches of different sizes and shapes made to suit the area of application. The drug is held in a reservoir between an outer layer and a porous membrane. This membrane is smeared with an adhesive to hold on to the area of application. The drug slowly diffuses through the membrane and percutaneous absorption takes place. The rate of absorption is constant and predictable. Highly potent:
- Pulmonary epithelium and mucous membranes of the respiratory tract and are also absorbed through these membranes. (because small quantity is sufficient) and short acting (effect terminates quickly after the unit is removed) drugs are suitable for use in such systems
- Sites of application are chest, abdomen, upper arm, back or mastoid region, e.g. hyoscine, nitroglycerine fentanyl, estrogen, testosterone transdermal patches
Advantages
- Duration of action is prolonged
- Provides constant plasma drug levels
- Patient compliance is good
- Inunction: in this route of administration, the drug is rubbed into the skin and it gets absorbed to produce systemic effects
- Iontophoresis: in this procedure, galvanic current is used for bringing about penetration of lipid insoluble drugs into the deeper tissues where its action is required, e.g. salicylates. Fluoride iontophores is used in the treatment of dental hypersensitivity
- Jet injection as absorption of drug occurs across the layers of the skin, dermojet may also be considered as a form of transdermal drug administration
