PHYTOTHERAPY RESEARCH Phytother. Res. 17, 376 – 379 (2003) Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/ptr.1164 Copyright © 2003 John Wiley & Sons, Ltd. Received 31 October 2001 Received 18 November 2001 Accepted 1 October 2001 John Wiley & Sons, Ltd. In vitro Antagonistic Activity of Monoterpenes and Their Mixtures Against ‘Toe Nail Fungus’ Pathogens MONOTERPENES ON TOE NAIL FONGUS Russel S. Ramsewak 1, †, Muraleedharan G. Nair 1 *, Manfred Stommel 2 and Louise Selanders 2 1 Bioactive Natural Products and Phytoceuticals Laboratory, Department of Horticulture and National Food Safety and Toxicology Center, Michigan State University, East Lansing, Michigan, USA 2 College of Nursing, Michigan State University, East Lansing, Michigan, USA The antibiotic effect of the active ingredients in Meijer™ medicated chest rub (eucalyptus oil, camphor and menthol) as well as the inactive ingredients (thymol, oil of turpentine, oil of nutmeg and oil of cedar leaf) were studied in vitro using the fungal pathogens responsible for onychomycosis, such as the dermatophytes Tricophyton rubrum, Trichophyton mentagrophytes, Microsporum canis, Epidermophyton floccosum and Epidermophyton stockdale. The zones of inhibition data revealed that camphor (1), menthol (2), thymol (3) and oil of Eucalyptus citriodora were the most efficacious components against the test organisms. The MIC 100 for mixtures of these four components in various carrier solvents revealed that formulations con- sisting of 5 mg/mL concentrations of each have a potential to be efffective in controlling onychomycosis. Copyright © 2003 John Wiley & Sons, Ltd. Keywords: terpenes; toe nail fungus; onychomycosis; dermatophytes; Eucalyptus citriodora. INTRODUCTION Onychomycosis (Tinea unguium), commonly referred to as toe nail fungus, is an infection usually determined by the appearance of a thickened, yellow or brown discoloured and friable nail plates (Zaias et al., 1996). It is caused by dermatophytes such as Trichophyton rubrum, Trichophyton mentagrophytes, Microsporum canis, Epidermophyton floccosum and Epidermophyton stockdale, which represent about 90% of the cases. Yeasts (Candida albicans, Candida parapsilosis and Candida kruseii) and nondermatophyte moulds such as Scytalidium hyalinum, Scytalidium dimidiatum, Fusarium oxysporum, Fusarium moniliforme, Acremonium chry- sogenum, Acremonium strictum, Aspergillus terreus, Aspergillus flavus and Scopulariopsis brevicaulis are responsible for 7% and 3% of cases, respectively. These organisms infect the stratum corneum of the skin, hair and nails (Zaias et al., 1996; Tom and Kane, 1999; Lugo- Somalinos and Sanchez, 1992). Onychomycosis never resolves spontaneously and recurrence after treatment is very common. Treatment is difficult because of the unique properties of the nail unit. Thus, an effective antifungal agent must enter the affected tissue and persist there in high concentrations. The existing therapies must be continuous and used until the infected nail grows out and even after this lengthy treatment low cure rates and quick relapse times are common (Zaias et al., 1996; Tom and Kane, 1999). Treatments with topical creams are not as effective as oral treatments and prolonged periods of application are required. Griseofulvin (Grifulvin V®), terbinafine (Lamisil®) and itraconazole (Sporonex®) are the drugs usually used for oral treatment. The current laboratory study was conducted in response to requests from the clinical faculty in the College of Nursing (CON) at Michigan State University. For several years, the CON faculty had been operating foot care clinics for elderly individuals in mid-Michigan communities. During that time, hundreds of individuals with varying degrees of fungal nail infections sought foot care services. Initially, over-the-counter topical treat- ments were suggested as possible remedies. Patients often returned for subsequent foot care and reported that they had not carried through with treatment of over-the-counter antifungal medications because they could not see any improvement. A ‘folk remedy’ was reported to the nurses by one of the individuals receiving foot care at the clinics. An elderly gentleman reported that he had totally cleared a bad case of toe nail fungus in several months by daily applying Vick’s Vapo-Rub™ to the affected nails. Sub- sequently, nurses suggested this treatment to several other patients at the foot clinics who had toe nail disfigurement due to fungal infection. The ensuing clin- ical observations were suggestive, though they were not part of a formalized clinical trial with control group. Thus, several bioassays were conducted on the various fungal pathogens with the ingredients of the vapo-rub in order to determine their efficacies and MIC 100 on the pathogens responsible for onychomycosis. * Correspondence to: Dr M. G. Nair, 173 National Food Safety and Toxicology Center, Michigan State University, East Lansing, Michigan 48824, USA. E-mail: nairm@msu.edu † Present address: Department of Chemistry, University of the West Indies, St. Augustine, Trinidad and Tobago. Contract/grant sponsor: Michigan State University Foundation. Contract/grant sponsor: Michigan State University Center for Plant Products.