Topical drug delivery
For chemical agents, carriers like liposomes and nanotechnologies are used to enhance the absorption of topical drugs.
[4] Besides using carriers, other factors such as pH, lipophilicity, and drug molecule size govern the effectiveness of topical formulation.
[4] In 1938, Zondek successfully managed urogenital infections after applying chloroxylenol on the skin by the use of disinfectant in ointment form.
After the development of toxicology, a mathematical model was also created for skin diffusion coefficient formulated by Michaels.
[8] Stratum corneum's function includes prevention of water loss in skin and inhibit the penetration of foreign molecules into the dermal layers.
The shortcut pathway allows the drug molecules to first pass the stratum corneum barrier via hair follicles.
The expression illustrates the transportation of topical drug molecules across the stratum corneum membrane through diffusion.
It is known as the "first cut" where the drug molecules will be partitioned into the sweat gland to bypass the stratum corneum barrier.
[1] If the drug molecules is not transported via the "first cut", it is usually remains in the stratum corneum's bilayered lipids, where the drug molecules transport through either the transcellular route or paracellular route into the deeper area of the skin like subcutaneous layer.
[10] When the topical drug molecules transport via the paracellular route, it needs to travel across the stratum corneum, which is a highly fat region, but between the cells.
Transcellular route transports the drug molecule into the bilayered lipid cells found in stratum corneum.
[1][11] During the transportation of the topical drug molecules, it can bind to the keratin that exists as one of the skin components in the stratum corneum.
[12] One common example is thearylamine-type hair dye, after it is applied topically, it will undergo metabolism in the skin through enzyme N-acetyltransferase, thus resulting in a N-acetylated metabolite.
They may eventually form atoxic compound that reaches to the systemic circulation and causes damage to the skin layers.
[13] The longer the topical drug remains in the skin, the greater amount of it will be metabolized by the underlying enzymes.
To reduce such an effect, the topical drug needs to remain on the skin for a shorter period of time.
The smaller of the drug molecular weight or particle size, the higher rate of its diffusion and absorption into the skin.
With this structure, its function is to trap hydrophilic or lipophilic drug molecules within the spherical bilayers.
[15] The Use of liposome as carrier enhances the overall permeability of topical drug into the skin to reach the target site.
[18] The drug is loaded into liposome and this carrier enhances the penetration of amphotericin B into the skin, regardless of its molecular weight.
The use of nanoemulgel enhances patient compliance because the use of gel is less greasy than traditional cream or ointment, hence there is less incident in skin irritation.
[20] Micro-needle belongs to the physical enhancer to improve absorption of topical drug molecules into the skin.
