R. Lázaro, M. Mallandrich, P. Flórez, E. González-Mira, A.C. Calpena. Department of Pharmacy and Pharmaceutical Technology, Unit of Biopharmacy and Pharmacokinetics, Faculty of Pharmacy, University of Barcelona, Barcelona, Spain. Cetirizine dihydrochloride is a second generation H1 antihistamine, with no sedating characteristics. At the site of action it causes vasoconstriction leading to a decreased vascular permeability. It also diminishes redness, swelling and pruritus associated with allergic reactions. Hydrogels are colloidal systems formed by hydrophilic polymers and water, which can be used as topical drug delivery systems. At present, there are no semisolid formulations with cetirizine for topical administration. An alternative treatment for skin allergic reactions could be developed, consisting of a gel applied directly onto the affected area. Rheological study: Flow curves Flow curves show a plastic and tixotropic behaviour, which facilitates the hydrogel’s spreadability onto the skin. Stability study: The formulation presented its characteristic fluctuation character, however, no destabilisation was observed. Skin permeation: There were no permeated quantities of cetirizine from the hydrogel. However, 23.44 μg/g of skin/ cm² were found retained in the skin. 1 Aulton ME. Pharmaceutics, the science of dosage form design. Churchill Livingstone. 2nd Ed. 2002; 49-51, 528-529. 2 Beale JM, Block JM. Wilson & Gisvold’s Textbook of organic medicinal and pharmaceutical chemistry. Lippincott Williams & Wilkins. 11th Ed. 2004; 714. 3 Claudia Ciurlizza Celis. Study of transdermal penetration of cetirizine. Scholarship College of Pharmacy Barcelona, September 2007. 4 European Pharmacopoeia 6th Edition. European ADirectorate for the Quality of Medicines & HealthCare. 2007; 1479. 5 Guidance for Industry, Nonsterile Semisolid Dosage Forms, Scale-Up and Postapproval changes, FDA – Center for Drug Evaluation and Research, 1997; 19-21. 6 PubChem: http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=2678&loc=ec_rcs 7 Shimizu T, Nishira J, Watanabe H, Abe R, Isibashi T, Shimizu T. Cetirizine, an H1-receptor antagonist, suppresses the expression of macrophage migration inhibitory factor: its potential anti-inflammatory action. Clin. Exp. Allergy. 2004 Jan; 34(1): 103-109. Elaboration method: The formulation was prepared by weighing and mixing of different components and agitation by magnetic stirrer. Characterization of natrosol hydrogel: •Rheological study: Rotational viscosimeter (Haake VT 500) was used for flow curves evaluation. • Skin permeation: Franz-type diffusion cells (Crown Glass Co. Sommerville, N.J., USA) with a diffusion area of 2,54 cm2 and abdominal human skin from Hospital de – SCIAS (Barcelona, Spain). • Determination and quantification of Cetirizine HCl: A Waters (Milford, Mass., USA) LC module I plus instrument. • Hydrogel stability study: multiple light scattering using TurbiscanLab® . • Linear regression analysis: using GraphPad for Windows 2008. Components % Cetirizine dihychloride 5 Natrosol® 3 NaOH q.s. pH ≈ 6 Purified water with parabens. q.s. C:\TLAb-EXPERT\Paloma\TScan295.lab S c a n N a m e d N o - r e f T r a n s m i s s i o n - p r e d e f i n e d z o o m 0 % 2 0 % 4 0 % 6 0 % 8 0 % 1 0 0 % 0 : 0 0 : 0 0 2 : 0 0 : 0 0 3 : 0 0 : 0 0 4 : 0 0 : 0 0 6 : 0 0 : 0 0 7 : 0 0 : 0 0 8 : 0 0 : 0 0 1 0 : 0 0 : 0 0 1 1 : 0 0 : 0 0 1 2 : 0 0 : 0 0 1 3 : 0 0 : 0 0 1 5 : 0 0 : 0 0 1 6 : 0 0 : 0 0 1 7 : 0 0 : 0 0 1 9 : 0 0 : 0 0 2 0 : 0 0 : 0 0 2 1 : 0 0 : 0 0 2 2 : 0 0 : 0 0 2 4 : 0 0 : 0 0 C:\TLAb-EXPERT\Paloma\TScan295.lab S c a n N a m e d N o - r e f B a c k s c a t t e r i n g - p r e d e f i n e d z o o m 0 % 5 % 1 0 % 1 5 % 2 0 % 2 5 % 0 : 0 0 : 0 0 2 : 0 0 : 0 0 3 : 0 0 : 0 0 4 : 0 0 : 0 0 6 : 0 0 : 0 0 7 : 0 0 : 0 0 8 : 0 0 : 0 0 9 : 0 0 : 0 0 1 1 : 0 0 : 0 0 1 2 : 0 0 : 0 0 1 3 : 0 0 : 0 0 1 4 : 0 0 : 0 0 1 6 : 0 0 : 0 0 1 7 : 0 0 : 0 0 1 8 : 0 0 : 0 0 1 9 : 0 0 : 0 0 2 1 : 0 0 : 0 0 2 2 : 0 0 : 0 0 2 3 : 0 0 : 0 0 2 4 : 0 0 : 0 0 No permeated quantities of cetirizine were found from the skin permeation experiment. Nevertheless, 23.44 μg/g of skin/ cm² were found retained in skin, which opens the possibility to investigate whether or not these quantities can cause a local antihistaminic activity. Knowing that antihistamines applied topically usually lead to sensitization of the patient, further biopharmaceutical and toxicological studies are needed. Material Acknowledgements: MAT2010-19877 Project Ministerio de Ciencia y Innovación.