Susceptibility of Chlamydia trachomatis to Excipients Commonly Used in Topical Microbicide Formulations

Abstract

Commonly used "inactive" pharmaceutical excipients were tested in a previously developed minimum cidal concentration assay to assess their ability to kill Chlamydia trachomatis topically. Sixteen excipients were evaluated in these studies under various conditions. A range of activities was found among the excipients that could be tested in our assay system.Promising topical antimicrobial agents that are active against sexually transmitted infection pathogens have been identified (1, 10, 11), but these agents must be delivered in an acceptable dose and formulation such as a cream, gel, or foam. These drug delivery systems contain excipients that serve multiple functions, including the enhancement of product stability, efficacy, and acceptability to the patient. Excipients can be classified into a number of categories, including preservatives, solvents, antioxidants, and gelling agents. Although excipients are important components of topical microbicide products and are also known to possess antimicrobial activity (4, 12), their activity against Chlamydia trachomatis have not yet been determined. Here we use the previously described (1, 10, 11) minimal cidal concentration (MCC) assay, designed to test the direct action of microbicides against the extracellular, infectious C. trachomatis elementary bodies (EBs), to measure the inherent antichlamydial activity of potential excipients for formulation of active agents into topical microbicide products.These studies used C. trachomatis serovar L2 (434/Bu). The bacterium was propagated in mouse McCoy fibroblasts (ATCC CRL 1696), purified on Renografin (6), and frozen at Ϫ70°C in a sucrose-phosphate-glutamate cryopreservative buffer (SPG) (8). The serotype of this strain was verified by a plate typing method (13). This strain was used because it is easier to grow and more sensitive to some topical microbicides than other strains (3).Excipients evaluated in these studies represented four principal categories. The antioxidants evaluated were vitamin E (Spectrum, Gardena, Calif.), EDTA (Sigma, St. Louis, Mo.), and butylated hydroxyanisole (Spectrum). The preservatives tested were propylparaben (Spectrum), methylparaben (Spectrum), sodium benzoate (Spectrum), potassium benzoate (Spectrum), benzalkonium chloride (BAK; Sigma), benzoic acid (Spectrum), sorbic acid (Spectrum), and PEG 400 (Spectrum). The acidifying agents were lactic acid (Spectrum) and citric acid (Sigma). Gelling agents studied were three carrageenan products, Viscarin 328, Gelcarin 812, and Seaspen (FMC, Newark, Del.). These excipients were evaluated at three concentrations (lower than the average, average, and higher than the average normal usage level in vaginal products) (9), two pH values (pH 5 and 7), and two time points (5 and 120 min). Most excipients were dissolved in SPG, while a few (sorbic acid, methylparaben, and benzoic acid) were solubilized in ethyl alcohol and then diluted in SPG. The concentration of ethyl alcohol used, however, was shown to have no activity against the chlamydial EBs (data n...

Susceptibility of Chlamydia trachomatis to the Excipient Hydroxyethyl Cellulose: pH and Concentration Dependence of Antimicrobial Activity

“…The buffered pH levels used in the current study were chosen to provide a point of comparison with the work of Lampe et al (8). While studies performed at pH 4 also demonstrated inhibition for serovar LGV/L2 (data not shown), the effect was less pronounced than that at pH 5 or 7.…”

“…Since new preventative antimicrobials could prevent chlamydial infection, there is much effort to develop microbicides and related compounds (7,20). Recently, a number of reports have highlighted the in vitro antichlamydial properties of polysaccharide-based chemotherapeutics and excipients (2,8,10,19). Studies on the basis of the antimicrobial properties of polysaccharides highlight the need for the use of excipient-only controls when the effectiveness of new antimicrobials is tested and contribute to our understanding of the molecular mechanism of chlamydial adhesion to polysaccharides or glycoproteins on the surface of host cells.…”

“…Excipients are an inherent part of drug delivery systems used for both topical vaginal medications and contraceptives and fall into four principal classes: antioxidants, preservatives, acidifying agents, and gelling agents (8). Gelling agents are frequently polysaccharides, which are also adhesins through which bacterial pathogens bind to host cells.…”