Abstract
Usnic acid is known for its remarkable antimicrobial activity. The aim of this research was to formulate hydrogel of usnic acid and evaluate the antibacterial activity against Propionibacterium acne. Due to low solubility of usnic acid, solid dispersion was prepared using PVP K-30. In this study, intact usnic acid (UA) and usnic acid-solid dispersion (UA-SD) was formulated in hydrogel using several gelling agents: Aqupec HV-505, sodium alginate and HPMC K 100M. Concentration of each gelling agent was optimized for hydrogel base. All of hydrogel base showed homogenous gel, pH at range 5.37–6.33 and viscosity in range 259.07–10,759.00 cps. Hydrogel was prepared by dispersing 1% intact UA and 3% UA-SD in three different gelling agents. The hydrogel was evaluated for pH, viscosity, stability test for two months and microbiology test. The amount of usnic acid in hydrogel was determined by spectrophotometry UV-Vis. Hydrogel UA showed non-homogenous gel, while hydrogel usnic UA-SD was homogenous. The pH of all hydrogel was in range 5.5–6.4 and viscosity was 2,017.03–3,866.52 cps. All the hydrogel was stable and diameter inhibition of hydrogel was in a range 20–32 mm. The amount of usnic acid in hydrogel was in range 96.9–99.23%. In conclusion, hydrogel UA-SD is promising preparation in handling acne.
Highlights
Usnic acid, a secondary metabolite produced by Usnea sp, is already known for remarkable pharmacological activities including: anti-bacteria [1], antivirus [2], anti-proliferation [3], anticancer [4], antioxidant [5], antipyretic and analgesic [6] and anti-inflammation [7]
Usnic acid has a significant activity against anaerobic Gram positive bacteria including Propionibacterium species [9,10]
Preparation of hydrogel is influenced by the form of usnic acid used, which solid dispersion of usnic acid with PVP K-30 provides better result in appearance compared to intact usnic acid
Summary
A secondary metabolite produced by Usnea sp, is already known for remarkable pharmacological activities including: anti-bacteria [1], antivirus [2], anti-proliferation [3], anticancer [4], antioxidant [5], antipyretic and analgesic [6] and anti-inflammation [7]. Usnic acid has two optical isomers, the (+) and (−) usnic acid, which affected its activity against microorganisms Both of enantiomers are potent against Gram-positive bacteria, while the (−) usnic acid has typical activity as a natural herbicide [8]. Propionibacterium acne, a Gram-positive and facultative anaerobic bacterium, is one of the normal flora on the skin that in certain conditions can cause inflammation by producing lipases which break down fatty acids free of skin lipids, known as acnes [11]. A study has confirmed that usnic acid from Usnea barbata has ability to inhibit the growth of P. acnes at concentration ≥ 1 μg/mL [12]
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