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c) Odorless, tasteless, colorless
d) Compatible with most drugs and excipients
e) Inexpensive, and has good solvent properties
Types of penetration enhancers:
Alcohols and polyols (ethanol, propylene glycol).
Surfactants (Tween, Span, SLS).
Fatty acids (Oleic acid).
Amines and amides (Azone, N -methylpyrrolidone).
Terpenes (limonene).
Sulfoxides (dimethylsulfoxide).
Esters (isopropylmyristate).

Mechanism of permeation enhancers
Permeation enhancers can enhance the skin permeability by a variety of mechanisms,
including:

a. Interaction with intercellular lipids leads to disruption of their organization and
increases their fluidity

b. Extraction of lipids from the stratum corneum
c. Displacement of bound water
d. Loosening of horny cells
e. Delamination of stratum corneum
f. Enhancing solubility
g. Increasing partitioning into the stratum corneum
h. Interaction with intercellular protein, and keratin denaturation

• Prodrugs
Prodrugs are therapeutically inactive derivatives of therapeutically active drugs
A prodrug undergoes metabolism to produce the therapeutically active drug
A prodrug is more lipophilic than the parent drug and has different physicochemical properties
• Penetration enhancers
• Prodrug approach
Examples of transdermal prodrugs
Different prodrugs were developed for estradiol and "Transdermal Bioactive Hormone
Delivery" devices were developed

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