Amorphous cyclosporin A nanoparticles for enhanced dermal bioavailability

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Graphical abstractCylosporin A (CyA) was formulated as amorphous nanoparticle suspension to increase dermal penetration, e.g. applicable in psoriasis. The suspension consisted of 5% CyA in water, stabilized with vitamin E polyethylene glycol succinate (TPGS, Kolliphor® TPGS) and was produced by bead milling. The diameter of the bulk population was about 350 nm, laser diffraction diameter 99% was 690 nm. The suspension was physically stable over one year of storage at room temperature, and most important the amorphous state also remained stable. Despite the high dispersitivity and related large surface area in contact with water, the drug content reduced only by 5% over 1 year of storage. i.e. the formulation is feasible as commercial product with expiry date. The CyA nanoparticles and μm-sized CyA particles were incorporated into hydroxypropylcellulose (HPC) gels and the penetration studied into fresh pig ear skin applying the tape stripping method. At tape number 30, the penetrated cumulative amount of CyA from nanoparticles was 6.3 fold higher compared to the μm-sized raw drug powder (450.1 μg/cm2 vs. 71.3 μg/cm2). A theoretical mechanism is presented to explain the observed superiority in penetration. Based on amorphous CyA nanoparticles, dermal formulations for improved dermal CyA delivery seem to be feasible.

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