Formulations of benzoyl peroxide

Abstract

Benzoyl peroxide has been extensively used as a first line treatment for acne vulgaris with topical formulations ranging from solutions, gels, creams to washes. Optimal particle size distribution of active ingredients in topical formulations contribute to better dispersions and overall better therapeutic effect. The aim of this study was to identify the particle size distribution of benzoyl peroxide in three strengths of gels and one wash, by means of optical microscopy. Brightfield transmittance illumination and polarised contrasting technique were investigated to distinguish between the active ingredient and excipients in the final products. A comparative study between the illumination techniques was also conducted. The polarised mode was able to distinguish between benzoyl peroxide and the solid excipients within the formulation, whilst the brightfield illumination mode did not. Benzoyl peroxide particles observed with the polarised mode were more resolved, permitting the measurement of individual benzoyl peroxide particles in agglomerates. As a result, more particles were observed with the polarised mode (n=1532) compared to the brightfield mode (n=858). The mean standard deviation for particles measured with polarised mode (1.7) was lower than that with brightfield mode (4.6). Three strengths of gels and one wash were tested using the polarised mode, for which the particle size distributions, mean and standard deviation values were found and compared. Particle sizes for all four products ranged from 0.3 to 14 μm. The mean particle size of the tested products was 3.2 μm (±0.4 μm), with a standard deviation of 2 (± 0.2). Particle size distribution of the four products were D10 2 μm, D50 4 μm and D90 7 μm (±1 μm). The polarised illumination mode was found to be the most suitable technique for particle size determination. The evaluated products exhibited a similar particle size distribution.