topical drug delivery

How do drugs permeate the skin

• permeation occurs directly across the stratum corneum, which is also the main barrier to drug delivery via the route

• There is a ceramide rich lipid region that is complex and coonsitis of a multiple lamellar structure presenting hydrophobic and hydrophilic regions

Dosage forms in topical drug delivery

• dosage forms employed are typically lipid or semi solids

• Solutions

• Emulsions

• Suspensions

• Liquid dosage forms will have short residence time

Semi solid dosage forms

• Cream

• Ointments

• Gels

• Pastes

Other formulation are also used for topical drug delivery

• sprays

• Dusting powders

• Patches

Occlusivity

• the stratum corneum is the principal barrier to water loss from the skin

Micro dialysis

• involves insertion of dialysis tubing into the skin

• Perfusate pump through tubing

• Drug molecules enter perfusate

• Analysis

Tape stripping

• layers of the skin are successively removed using adhesive tape

• Relatively painless techque

• Drug on tape removed from solvent

Skin biopsy

• potentially painful fur to neuronal network in the dermis

Physiological response

• relies upon the drug having some forms physiological effect that can be observed, e.g vasodilation

Evaluation of topical drug delivery

• majority of topical evaluation is by in vitro methods often using fraz type diffusion cells

• Although we are quantifying what has permeated through the skin