j. Cosmet. Sci., 54, 239-250 (May/June 2003) Diffusion of preservatives from topical dosage forms' A comparative study ELISABETTA ESPOSITO, FABRIZIO BORTOLOTTI, CLAUDIO NASTRUZZI, ENEA MENEGATTI, and RITA CORTESI, Department of Pharmaceutical Sciences, University of Ferrara, 1-44100 Ferrara (E.E., F.B., E.M., R.C.), and Institute of Drug Chemistry and Technology, University of Perugia, 1-06100 Perugia (C. N.), Italy. Accepted for publication August 19, 2002. Synopsis A study of the diffusion of parabens from topical formulations is presented here. In particular, four different topical formulations, namely, a water-in-oil emulsion, an oil-in-water emulsion, and two hydrophilic gels (Pemulen gel and Carbopol gel) were produced, containing a mixture of three common parabens, namely, methylparaben (MP), ethylparaben (EP), and propylparaben (PP). An analytical method based on liquid extraction, followed by reversed-phase HPLC for the quantitative determination of MP, EP, and PP, was developed. The method allowed good separation of paraben mixtures and high percentages of recovery ( than 97%). The diffusion kinetics of parabens from the produced formulations was determined by an in vitro system based on a Franz cell assembled with a synthetic membrane, followed by a reversed-phase HPLC analytical method. The comparative study demonstrated that, in the case of emulsions, diffusion coefficients are a function of the substituent of preservatives: the higher the solubility, the higher the diffusion of parabens. On the contrary, in the case of the hydrophilic gels, the higher the parabens solubility, the lower the diffusion coefficients. The method described here could represent a means of controlling the extent of diffusion of parabens from topical formulations in order to minimize percutaneous absorption and to control the availability of microbes. INTRODUCTION The main deterioration factors in pharmaceutics or cosmetics can be divided into chemi- cophysical changes and microbial contamination. Among these, the importance of mi- crobial contamination is relevant for sanitary problems in dermal usage. Two strategies should be adopted in order to prepare microbiologically acceptable pharmaceutical formulations or cosmetic products: the minimization of the risks of contamination from sources and the addition of preservatives to the formulation. The use of preservatives is Address all correspondence to Elisabetta Esposito. 239

240 JOURNAL OF COSMETIC SCIENCE preferable in order to guarantee the long-term absence of contamination from formula- tions (1). Among the preservatives used in the pharmaceutical and cosmetic fields, the methyl, ethyl, propyl, and butyl esters and their sodium salts (parabens, USP) are probably the most widely used molecules (2,3), being active against molds, yeasts and, to a lesser extent, bacteria (4). In addition, parabens exhibit antimicrobial activity over a wide pH range (between 4 and 8). The activity of the parabens increases with the increasing chain length of the alkyl moiety and could be potentiated by the use of combinations of parabens, since an additive effect occurs. In order to preserve topical preparations, parabens are normally used in the concentration range of 0.02-0.3% (5,6). Besides the desirable requisites for a preservative to be suitable for use in a topical formulation (i.e., a wide spectrum of activity, bactericidal rather than bacteriostatic activity, a wide pH range, and temperature and water solubility), an essential feature should be the absence of toxic, irritant, or sensitizing activity (6,7). Parabens are nonmutagenic, nonteratogenic, and noncarcinogenic (7). Nevertheless, parabens, analogously to most other preservatives, may be harmful to consumers because of their tendency to induce allergic contact dermatitis, especially when they are included in topical formulations (8,9). The history of contact dermatitis from parabens falls into two phases, corresponding to their use first as medicaments and later as preservatives. As medicaments, Bonnevie (10) first reported a case of contact dermatitis from ethyl paraben used as an antifungal agent in a concentration of 5%. As preservatives, Sarkany first reported a case of sensitization from parabens (11). Since these reports, various investigators have found so many in- stances of sensitization to parabens in various topical therapeutic agents that most pharmaceutical manufacturers have removed parabens from topical therapeutic agents and have replaced them with other preservatives (12-14). In 1973 Fisher (15) reported several puzzling aspects, the socalled "paraben paradox," which is that parabens in topical therapeutic agents occasionally sensitize, whereas parabens in cosmetics are "safe." The explanation of this seeming paradox is that cos- metics are usually applied to normal skin, whereas therapeutic agents are applied to inflamed, eczematous, excoriated, or otherwise damaged skin. However, a case of a patient with hypersensitivity to parabens in several cosmetic creams and several cases of immediate-type hypersensitivity to parabens have been reported (16-18). With regard to the sensitizing effects related to the topical administration of parabens, it is fundamental that an i, vitro method should be able to determine the extent of parabens diffusion from topical formulations. This paper describes (a) the production of four different topical formulations, namely, a water-in-oil emulsion, an oil-in-water emulsion, and two hydrophilic gels (Pemulen gel and Carbopol gel), containing a mixture of three common parabens (b) an analytical method based on liquid extraction and reversed-phase HPLC for the quantitative de- termination of MP, EP, and PP in semisolid formulations and (c) the use of an in vitro system based on a Franz cell to study the diffusion of the different parabens from the formulations.