title: Dermal nanocrystals from medium soluble actives - physical stability and stability affecting parameters.
abstract: Nanocrystals are meanwhile applied to increase the dermal penetration of drugs, but were applied by now only to poorly soluble drugs (e.g. 1-10 μg/ml). As a new concept nanocrystals from medium soluble actives were produced, using caffeine as model compound (solubility 16 mg/ml at 20 °C). Penetration should be increased by (a) further increase in solubility and (b) mainly by increased hair follicle targeting of nanocrystals compared to pure solution. Caffeine nanocrystal production in water lead to pronounced crystal growth. Therefore the stability of nanocrystals in water-ethanol (1:9) and ethanol-propylene glycol (3:7) mixtures with lower dielectric constant D was investigated, using various stabilizers. Both mixtures in combination with Carbopol 981 (non-neutralized) yielded stable nanosuspensions over 2 months at 4 °C and room temperature. Storage at 40 °C lead to crystal growth, attributed to too strong solubility increase, supersaturation and Ostwald ripening effects. Stability of caffeine nanocrystals at lower temperatures could not only be attributed to lower solubility, because the solubilities of caffeine in mixtures and in water are not that much different. Other effects such as quantified by reduced dielectric constant D, and specific interactions between dispersion medium and crystal surface seem to play a role. With the 2 mixtures and Carbopol 981, a basic formulation composition for this type of nanocrystals has been established, to be used in the in vivo proof of principle of the new concept.
authors.affiliation: Institute of Pharmacy, Department of Pharmaceutics, Biopharmaceutics & NutriCosmetics, Freie Universität Berlin, Berlin, Germany.
authors.forename: Xuezhen
authors.initials: X
authors.lastname: Zhai
authors.affiliation: Department of Dermatology, Venerology and Allergology, Center of Experimental and Applied Cutaneous Physiology (CCP), Charité-Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Lademann
authors.affiliation: Institute of Pharmacy, Department of Pharmaceutics, Biopharmaceutics & NutriCosmetics, Freie Universität Berlin, Berlin, Germany; Fachhochschule/University of Applied Sciences Kaiserslautern, Pirmasens, Germany.
authors.forename: Cornelia M
authors.initials: CM
authors.lastname: Keck
authors.affiliation: Institute of Pharmacy, Department of Pharmaceutics, Biopharmaceutics & NutriCosmetics, Freie Universität Berlin, Berlin, Germany. Electronic address: nanoteam@gmx.com.
authors.forename: Rainer H
authors.initials: RH
authors.lastname: Müller
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D000287:Administration, Topical; D002110:Caffeine / Q000008:administration & dosage*; D003460:Crystallization; D004355:Drug Stability; D000431:Ethanol / Q000737:chemistry; D018859:Hair Follicle / Q000187:drug effects*; D006801:Humans; D053758:Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D011108:Polymers / Q000737:chemistry; D011409:Propylene Glycols / Q000737:chemistry; D012995:Solubility; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D000180:Acrylic Resins; C516894:Carbopol 981; D011108:Polymers; D011409:Propylene Glycols; D014867:Water; C012504:polypropylene glycol; D002110:Caffeine; D000431:Ethanol
keywords: Caffeine; Caffeine (PubChem CID: 2519); Dermal application; Medium soluble drugs; Nanocrystals; Penetration enhancement; Recrystallization