Methylisothiazolinone (MI) is one of the most used preservatives in shampoos and also one of the most effective. A preservative mixture known as Kathon™ CG is commercially available. It contains 5-chloro-2-methyl-4-isothiazolin-3-one (CMI) and 2-methyl-4-isothiazolin-3-one (MI) (3:1) and stabilizers. The aim of this study is to evaluate the influence of formulation factors in the quantification and stability of isothiazolinones in shampoos. Two shampoo bases containing Kathon™ CG as a preservative were prepared. Some ingredients that are at risk of interfering with the preservative stability were added to these formulations. The preservative was quantified by HPLC-DAD (High-performance liquid chromatography with a diode-array detector) after preparation of the formulation and after storage at room temperature and at 40 °C. The addition of magnesium silicate proved to be essential for the breakdown of the interaction between the matrix and the analytes in the extraction procedure. The content of CMI/MI decreased right after preparation indicating that immediate interactions between CMI/MI and the ingredients may have occurred after preparation resulting in a decrease in the preservative concentration. Detrimental interactions between the ingredients, regarding the stability of the isothiazolinones were detected immediately after preparation and over time resulting in the reduction of CMI/MI concentration in these cosmetic shampoos.

We aimed to incorporate Thymbra capitata essential oil (TCEO), a potent antimicrobial natural product against bacterial vaginosis (BV)-related bacteria, in a suitable drug delivery system. We used vaginal sheets as dosage form to promote immediate relief of the typical abundant vaginal discharge with unpleasant odour. Excipients were selected to promote the healthy vaginal environment reestablishment and bioadhesion of formulations, while the TCEO acts directly on BV pathogens. We characterized vaginal sheets with TCEO in regard to technological characterization, predictable in vivo performance, in vitro efficacy and safety. Vaginal sheet D.O (acid lactic buffer, gelatine, glycerine, chitosan coated with TCEO 1% w/w) presented a higher buffer capacity and ability to absorb vaginal fluid simulant (VFS) among all vaginal sheets with EO, showing one of the most promising bioadhesive profiles, an excellent flexibility and structure that allow it to be easily rolled for application. Vaginal sheet D.O with 0.32 µL/mL TCEO was able to significantly reduce the bacterial load of all in vitro tested Gardnerella species. Although vaginal sheet D.O presented toxicity at some concentrations, this product was developed for a short time period of treatment, so this toxicity can probably be limited or even reversed when the treatment ends.

Background/Objectives: Cytolytic vaginosis or, classically, Doderlein’s cytolysis is characterized by significant growth of species of the Lactobacillus genus, which leads to high amounts of lactic acid in the vaginal environment. Lactobacillus crispatus has been proposed as a key pathogen in this clinical condition. The symptomatology of cytolytic vaginosis is commonly confused with that of vulvovaginal candidosis, leading to inadequate and ineffective azole therapies. Nevertheless, historically, the use of sodium bicarbonate intimate baths was an effective way to reduce the symptoms of cytolytic vaginosis. Methods: In this study, four HPMC gel prototypes were developed, containing sodium bicarbonate concentrations ranging from 4% to 7% (w/w). These gels were evaluated for their physicochemical properties, antimicrobial activity, interference with lactobacilli adhering to cells, and cellular and tissue biocompatibility. Results: The gels presented pH values of around 9.0, and osmolality between 706 mOsm/kg (F4) and 1065 mOsm/kg (F7). The viscosity upon heating to physiologic temperature and dilution with simulated vaginal fluid was highly affected by the concentration of sodium bicarbonate. Gels with higher sodium bicarbonate concentrations (F6 and F7) were not shown to be stable in these conditions. All formulations exhibited effective antimicrobial activity against seven L. crispatus strains, with MIC values ranging from 6.25% to 25% (v/v) in terms of dilution. Additionally, the 4% (w/w) gel significantly interfered with the adhesion of L. crispatus to epithelial cells in competition and exclusion assays, reducing adhesion by more than 90% in relation to the control. Cytotoxicity tests on the Hec-1A, HeLa, and VK2/E6E7 cell lines indicated that the F4 and F5 gels demonstrated lower cytotoxicity levels compared to those with higher concentrations. Furthermore, ex vivo assays using porcine vaginal tissue confirmed that the 4% gel was non-toxic at a 25% (v/v) dilution. Conclusions: Based on these results, the 4% (w/w) sodium bicarbonate gel (F4) emerges as a promising therapeutic option for cytolytic vaginosis, offering effective bacterial interference, favourable physicochemical properties, and biocompatibility suitable for vaginal application.