Influence of non-ionic, ionic and lipophilic polymers on the pH and conductivity of model ointments, creams and gels.

Background: The pH of the skin surface is usually between 5.4 and 5.9 and functions as a barrier against bacteria and fungi; thus, the composition of the topically applied drug form may be of high importance for proper medication.

Objectives: To evaluate the influence of the measurement conditions in aqueous solutions of ointments, creams, and gels, which include polymeric components, on the pH and conductivity results.

Material and methods: The pH and electrolytic conductivity of aqueous dispersions of commercially available ointments, creams and gels were tested and compared to reference vehicles.

Results: The results of the dilution method measurements of the pH and electrolytic conductivity of the ointment preparations are highly diverse, ranging from 5.88 to 6.27, whereas the reference pH for Unguentum simplex was between 5.40 and 5.43. Furthermore, the measurements of the pH and electrolytic conductivity with the dilution method for creams did not provide repeatable results with a small sample size, and the pH of commercial preparations was in the range between 5.79 and 6.37, compared to the reference pH of 5.23-5.46. However, the dilution method for measurements of the pH and electrolytic conductivity was suitable for hydrogel preparations and the obtained results were repeatable in the range of 6.11-6.90, while the reference preparations were in the range of 5.19-5.62.

Conclusions: Evaluation methods of the electrolytic conductivity and pH of the preparations applied on the skin should be further evaluated; however, the pH of the commercial preparation seems to differ from the physiological skin pH, which covers the range of reference preparations.