Phospholipid-Based Microemulsions for Cutaneous Imiquimod Delivery

Area of Science:

• Pharmaceutical Sciences
• Dermatology
• Materials Science

Background:

• Imiquimod (IMQ) is an immune response modifier with antiviral and antitumor applications.
• Poor solubility and skin penetration limit IMQ's topical efficacy.
• Novel drug delivery systems are needed to enhance topical IMQ delivery.

Purpose of the Study:

• To develop imiquimod-loaded microemulsions (MEs) using phospholipids and oleic acid.
• To enhance the epidermal penetration of IMQ for topical administration.
• To evaluate the efficacy and safety of these novel MEs.

Main Methods:

• Construction of pseudo-ternary phase diagrams to identify microemulsion regions.
• Characterization of microemulsions, including conductivity and rheological measurements.
• Ex vivo human skin permeation studies and stratum corneum analysis using FTIR and TEWL.

Main Results:

• A stable, bicontinuous microemulsion (ME1) with Bingham rheology was formulated.
• ME1 delivered comparable IMQ amounts to the epidermis as a commercial product, but with a 5-fold lower dose.
• No IMQ was detected in the acceptor phase, indicating reduced systemic absorption risk.
• ME1 temporarily disrupted the stratum corneum barrier, with full recovery within 5 hours.

Conclusions:

• Phospholipid and oleic acid-based microemulsions are effective for topical IMQ delivery.
• These MEs offer improved skin penetration and a potentially safer systemic absorption profile.
• This formulation represents a promising alternative for topical imiquimod administration.