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Technical Report: In Vitro Assessment of the Antimicrobial Activity of Clarifying™ Base against Propionibacterium acnes

The purpose of this study is to characterize the antimicrobial activity of Clarifying Base and benzoyl peroxide 5% in Clarifying Base against P. acnes, using the broth macrodilution method for determining MIC. Results showed that Clarifying Base has the ability to inhibit the growth of P. acnes at a concentration of 15% when used alone, and 10% when in conjunction with benzoyl peroxide. These results suggest that Clarifying Base would be an ideal vehicle for acne preparations, due to its favorable characteristics versus P. acnes.


Acne vulgaris (also known as acne) is a chronic dermatological condition characterized by blockage and/or inflammation of pilosebaceous follicles, hair follicles that are associated with sebaceous glands (oil glands) within the skin [1]. Acne can stem from multiple factors such as overabundance of the hormone 5a-dihydrotestosterone (DHT) in the skin, which can stimulate increased sebum (oily substance) production by sebaceous glands. The accumulation of sebum in the skin can clog pores and induce an anaerobic environment within pilosebaceous follicles to favor the overgrowth of P. acnes, Grampositive anaerobic bacteria that can trigger the development of inflammatory acne lesions [2, 3].  Acne is most commonly treated topically using one or a combination of medications to reduce sebum production, increase cell turnover, and eliminate P. acnes [1]. Clarifying Base is a proprietary emulsion system developed as a delivery vehicle (base) for compounded preparations made for acne patients, used either alone, or as a base for the incorporation of different active pharmaceutical ingredients.Clarifying Base contains 5-α Avocuta® (butyl avocadate), an ingredient obtained from esterification of avocado oil [4]. This could potentially lower the amount of DHT within the skin, which could indirectly reduce sebum production by sebaceous glands [4].

Clinical trials have also been conducted by Expanscience® Laboratories to evaluate the effects of 5-α Avocuta® on sebum production on the scalp and face. After 4 weeks of using 1% 5-α Avocuta® shampoo once every 2 days on the scalp, there was a 34% reduction in sebum secretions (Figure 1), with decreased dandruff, itching, and redness [5].  Within 3 weeks of applying 2% 5-a Avocuta® cream twice daily to the face, there was a mean of 30% reduction in sebum production through lipid scores measurements, 40% reduction in surface area of lipid spots through image analysis, and a mean of 31% improvement in the patients’ seborrhea (oily skin) via dermatological analysis [4]. Furthermore, a study conducted by Sharquie et al. also showed that 5-a Avocuta® was effective in the treatment of acne, with significant reduction in the number inflammatory lesions on the face after 14 weeks of treatment, as displayed in Figure 2 [6].


To assess the antimicrobial activity of Clarifying Base and benzoyl peroxide 5% in Clarifying Base, an inoculum of P. acnes was prepared prior to inoculation of samples. MIC was then detected using the broth macrodilution method.  Preparation of inoculum The surface of a suitable volume of solid agar medium was inoculated with a stock culture of P. acnes, obtained from American Type Culture Collection (ATCC®). The cultures were incubated at 30 to 35°C for 24 to 96 hr. The number of viable microorganisms per milliliter of inoculum suspension was determined by serial dilution in sterile phosphate-buffered saline, followed by procedures for counting the test organisms. 


Acne lesions are painful, itchy, and cosmetically undesirable for most patients, affecting their self-esteem and overall quality of life [1]. Since the proliferation of P. acnes within pilosebaceous follicles often induce the development of acne lesions [3], the inhibitory effects of Clarifying Base on P. acne, when used alone and in combination with benzoyl peroxide, suggests that this topical base may be a valuable base to consider for acne patients.

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