Comparative transcutaneous immunization with imiquimod‐containing ointments and potential of in vitro methods to predict effects

This work evaluates the transcutaneous in vitro and in vivo immunization efficacy of five commercially available 5% imiquimod containing formulations. The parameters included microscopic analysis, rheological properties, drug permeation across synthetic membranes of molecular weight cutoff 10 kDa and ablated murine skin with both 0.1  m HCl and a phthalate buffer pH 3.6 Ph.Eur./methanol 3/7 (v/v) as receiver solutions in a Franz‐diffusion cell model. For in vivo formulation characterization, the cytotoxic T‐cell activity and interferon‐γ production in C57BL/6 mice was determined ex vivo 24 h after transcutaneous administration. OVA 257−264 (SIINFEKL) from chicken albumin served as a target antigen. Microscopic images demonstrated differences with respect to the presence or absence of crystalline API. Rheological properties point to a roughly ten‐fold difference between the products at low shear rates. With regard to drug permeation across synthetic membranes, only ‘Nan Bo’ demonstrated equality compared with Aldara™, resulting in f1 and f2 values of 5.25 and 59.58, respectively. The drug permeation rates were maximum from Aldara™ across ablated murine skin. Furthermore, differentiation between the formulations containing crystalline and dissolved states of active imiquimod was possible using this model. The in vivo results yielded significant immunomodulating activities ( p  < 0.05) of multisource formulations compared with the untreated control group, however, the significance of differences between the formulations was dependent on the parameter of interest. A correlation plot of skin permeation versus in vivo immunostimulating activity yielded a slope significantly different from zero only in the case of the murine skin setup ( r between 0.421 and 0.669). Yet this correlation is deemed not satisfactory for formulation optimization. Copyright © 2012 John Wiley & Sons, Ltd.