(T0930-09-56) Cloudy with a Chance of Precipitation- An Investigation into Physiochemical Incompatibilities between Parabens and Polysorbate 80

Purpose: Parabens, a frequently used preservative system, and non-ionic surfactants, such as Polysorbate 80 (PS80), are commonly used together in a variety of dosage forms. Previous studies have shown that paraben microbial efficacy decreases in the presence of high concentrations of PS80 due to their propensity to bind within its micellular structure, thereby reducing the levels of available paraben in solution^1,2. Internally, previously uncharacterized appearance shifts caused by interactions between Methylparaben (MP) and Propylparaben (PP) at low concentrations of PS80 were observed. Our study seeks to investigate the physiochemical incompatibilities noted in aqueous solutions containing PS80 when combined with MP and PP.

Methods: PS80 was added dropwise to three aqueous solutions containing incrementally increasing concentrations of MP and PP. Notable appearance changes were recorded following dissolution, which were used to identify a range of 10 PS80 concentrations that bridge the previously noted appearance shift. Stock solutions containing either 0.3% w/w MP, 0.03% w/w PP, or a combination of both 0.3% w/w MP and 0.03% w/w PP were prepared. Water was used as a control to verify that any appearance changes could not be attributed solely to the concentration of PS80. These four solutions were combined with the selected PS80 concentrations to build a test matrix of 40 total samples. Samples were then filtered with 0.2µm PES sterile filters and assayed both pre and post filtration for MP and PP content, as appropriate. Additionally, appearance observations were taken for each sample following manufacturing and filtration. Retain samples of each product were stored at CRT in glass scintillation vials and periodically observed for appearance changes. At T=5 Months, retain samples with notable appearance shifts were centrifuged at 13,000 RPM for 5 minutes using a microcentrifuge and appearance observations of the resulting precipitate were recorded.

Results: Samples containing both MP and PP had the most dramatic appearance shifts when titrated with PS80, spanning from clear, colorless to hazy, slightly blue to opaque white then eventually returning to clear, colorless solutions. While these appearance changes occurred independent of the concentration of MP and PP, the intensity of the shift became more identifiable as these concentrations increased. A comparable appearance shift was noted when individual samples were prepared at a smaller scale (Figure 1). Following T=5 Months storage at CRT, the samples initially noted as visibly hazy or opaque formed a very fine precipitate at the bottom of the sample vials, which could easily be resuspended. A few samples that were clear at the time of the initial evaluation, increased in haziness following storage. Following centrifugation, these samples formed a fine precipitate and a clear, colorless supernatant (Figure 2). Control samples that were prepared with water and PS80 uniformly resulted in clear, colorless solutions. The sample set made with 0.03% w/w PP also resulted in clear, colorless solutions. Conversely, the samples made with 0.3% w/w MP turned slightly blue at 0.06% w/w PS80 and formed a crystalline precipitate between 0.1% and 0.4% w/w PS80 before returning to a clear, colorless solution at 0.5% w/w PS80 (Figure 1). This precipitate was larger and more granular when compared to the precipitate formed in the samples containing both MP and PP (Figure 2). Notably, the precipitate formed in the MP solution was observed almost immediately following manufacturing, whereas the precipitate in the solution containing both MP and PP developed over time. There was no marked change in appearance when these sample sets were stored for T=5 Months at CRT. For the test solutions without visible precipitation, no appearance change was noted between the pre and post filtration samples. The assay values for the samples made with 0.03% w/w PP solution and the combination 0.3% w/w MP and 0.03% w/w PP solution were consistent with the target amount of each respective ingredient, both as the concentration of PS80 increased and regardless of whether the sample was filtered prior to analysis. The assay data also confirmed that the precipitate noted in the 0.3% w/w MP solution samples between 0.1% and 0.4% w/w PS80 contained MP, as illustrated by the ~30% decrease in MP concentration (Figure 3).

Conclusion: As the concentration of PS80 increased, a notable appearance shift was observed in both solutions containing 0.3% w/w MP, followed by the subsequent precipitation of dissolved paraben. This observation was dependent on the presence of PP in the solution, particularly in relation to the time it took the precipitation to occur and the physical appearance of the precipitate. Additionally, as all the control samples resulted in clear, colorless solutions, it is apparent that this phenomenon is the result of a combined effect between these excipients and not solely related to the PS80 concentration. In summary, caution should be used when formulating products containing both parabens and PS80.

References: 1. Allen Jr LV, Poppovich NG, Ansel HC. Ansel’s pharmaceutical dosage forms and drug delivery systems. 10th ed., Philadelphia, PA, USA: Lippincott/Wolter Kluwer Health. 2013.
2. Schmitt, P. d. O., Fischer, A. F., da Silva, R. M. L., & Bella Cruz, A. (2022). Compatibility and efficiency of preservatives in emulsive cosmetics containing high surfactant content. Brazilian Journal of Pharmaceutical Sciences, 58, e191088. https://doi.org/10.1590/s2175-97902022e191088

Figure 1. Images taken of solution samples made with titrated concentrations of Polysorbate 80 at T=0. Pictured from top to bottom are the following solutions: 0.3% w/w Methylparaben and 0.03% w/w Propylparaben Solution; 0.3% w/w Methylparaben Solution; 0.03% w/w Propylparaben Solution, and the Control Solution (Water).

Figure 2. Images taken of precipitation observations noted in samples containing 0.10% w/w Polysorbate 80 following T=5 Months storage at CRT. The solution containing only Methylparaben yielded a large granular precipitate, whereas the solution containing both Methylparaben and Propylparaben resulted in a lesser amount of fine precipitate.

Figure 3. Graphs illustrating the changes in paraben concentration (%LC) with increasing concentrations of Polysorbate 80 (%w/w) both pre- and post-filtration with a 0.2µm PES sterile filter. Pictured on the left are the two solutions containing Methylparaben, on the right are the two solutions containing Propylparaben.