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Review
. 2022 Apr 5;9(4):158.
doi: 10.3390/bioengineering9040158.

Microemulsions and Nanoemulsions in Skin Drug Delivery

Eliana B Souto  1   2 , Amanda Cano  3   4 , Carlos Martins-Gomes  5   6 , Tiago E Coutinho  5   6 , Aleksandra Zielińska  7 , Amélia M Silva  5   6
Affiliations
Review

Microemulsions and Nanoemulsions in Skin Drug Delivery

Eliana B Souto et al. Bioengineering (Basel). .

Abstract

Microemulsions and nanoemulsions are lipid-based pharmaceutical systems with a high potential to increase the permeation of drugs through the skin. Although being isotropic dispersions of two nonmiscible liquids (oil and water), significant differences are encountered between microemulsions and nanoemulsions. Microemulsions are thermodynamically stable o/w emulsions of mean droplet size approximately 100-400 nm, whereas nanoemulsions are thermodynamically unstable o/w emulsions of mean droplet size approximately 1 to 100 nm. Their inner oil phase allows the solubilization of lipophilic drugs, achieving high encapsulation rates, which are instrumental for drug delivery. In this review, the importance of these systems, the key differences regarding their composition and production processes are discussed. While most of the micro/nanoemulsions on the market are held by the cosmetic industry to enhance the activity of drugs used in skincare products, the development of novel pharmaceutical formulations designed for the topical, dermal and transdermal administration of therapeutic drugs is being considered. The delivery of poorly water-soluble molecules through the skin has shown some advantages over the oral route, since drugs escape from first-pass metabolism; particularly for the treatment of cutaneous diseases, topical delivery should be the preferential route in order to reduce the number of drugs used and potential side-effects, while directing the drugs to the site of action. Thus, nanoemulsions and microemulsions represent versatile options for the delivery of drugs through lipophilic barriers, and many synthetic and natural compounds have been formulated using these delivery systems, aiming to improve stability, delivery and bioactivity. Detailed information is provided concerning the most relevant recent scientific publications reporting the potential of these delivery systems to increase the skin permeability of drugs with anti-inflammatory, sun-protection, anticarcinogenic and/or wound-healing activities. The main marketed skincare products using emulsion-based systems are also presented and discussed.

Keywords: microemulsions; nanoemulsions; skin bioavailability; skin drug delivery.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
From drug administration to its pharmacological effect. Upon administration (phase I), the drug is released from the pharmaceutical patch through the skin (phase II), after which the components are pharmaceutically available to be processed by the phase III-ADME system (absorption, distribution, metabolism and excretion). Once the drug reaches the systemic circulation, it becomes bioavailable to proceed to the target site and perform the pharmaceutical action (phase IV).
Figure 2
Figure 2
Representation of colloidal dispersions of o/w and w/o types.
Figure 3
Figure 3
Schematic representation of surfactant placement in the oil/water interface.
Figure 4
Figure 4
Production of an o/w emulsion.
See this image and copyright information in PMC

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