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Antifungal Fatty Acids and Essential Oils
Fatty acids have been known and used for centuries as antimicrobial agents, originally in the manufacture of soaps. In the last 50 years, however, they have found use both in vitro as yeast and mold inhibitors in food stuffs, and as topical, intestinal, and systemic antifungals. In recent years, both caprylic acid and undecylenic acid have been used to treat GIC. Undecylenic acid (10-undecenoic acid) is an eleven-carbon, mono-unsaturated fatty acid, C11H20O2. A substance found in the body (naturally occurring in sweat), undecylenic acid is produced commercially by the vacuum distillation of castor bean oil, as a result of the pyrolysis of ricinoleic acid. It has been used orally in humans as an unsuccessful treatment for psoriasis and neurodermatitis (神經性皮炎),35-37 and as an economical antifungal agent,38 as well as being commonly used as a topical antifungal in such over-the-counter products as Desenex®. Undecylenic acid has very low toxicity. In humans, as much as 20 grams per day has been taken orally with only mild gastrointestinal symptoms,36 and up to 400 mg/kg/day has been given orally to rats for 6-9 months, with no toxicity being noted.39 Caprylic acid, although present in small quantities in coconut oil, can be produced commercially from the oxidation (n.氧化) of octanol.40 Classified by some authors as an hepatic (a.肝髒的;治肝病的;肝髒色的) failure toxin when used intravenously,41 caprylic acid (C8H16O2), is a direct isomer (n.異構體) of the anticonvulsant (抗驚厥劑) valproic acid. Most organic fatty acids are fungicidal. As early as 1945, Wyss et al demonstrated that the greater the number of carbon atoms in the fatty acid chain, the greater the fungicidal activity, up to the point exceeding eleven carbons where solubility becomes the limiting factor.42 In 1954, Neuhauser evaluated both undecylenic and caprylic acids in vitro against C. albicans, and concluded caprylic acid was more effective.38 However, she used a questionable method of applying the fatty acids which may have rendered the results inaccurate. The pH of the test environment is critical to accurate in vitro testing of antifungal agents. Peck (n.啄痕;啄食;許多