Short-term topical therapy of experimental tinea pedis in guinea pigs with lanoconazole, a new imidazole antimycotic agent

Anti-Candida Activity of New Azole Derivatives Alone and in Combination with Fluconazole

The rate of Candida spp. infection is increasing, and resistance to azole antifungals is becoming increasingly common. Therefore, there is a need for discovery of new antifungal agents and for development of new modes of treatment using existing agents. In this in vitro study, the antifungal activity of two new imidazole derivatives was tested against a set of 20 Candida isolates, which included five different species. Treatment was carried out with the compound alone and in combination with fluconazole. Overall, we found that one of the new compounds, 31, was similar to fluconazole (FLC) in its efficacy against the Candida isolates and that compound 42 was superior to FLC. Furthermore, when combined with FLC, both compounds showed synergistic effects against 17 of the 20 tested isolates. No antagonistic interactions were observed. This study shows that our two new imidazole-derived compounds have good potential as general treatments for Candida infection and as a means to improve the current treatments with FLC.

Discovery of new imidazole derivatives containing the 2,4-dienone motif with broad-spectrum antifungal and antibacterial activity

A compound containing an imidazole moiety and a 2,4-dienone motif with significant activity toward several fungi was discovered in a screen for new antifungal compounds. Then, a total of 26 derivatives of this compound were designed, synthesized and evaluated through in vitro and in vivo antifungal activity assays. Several compounds exhibited improved antifungal activities compared to the lead compound. Of the derivatives, compounds 31 and 42 exhibited strong, broad-spectrum inhibitory effects toward Candida spp. In particular, the two derivatives exhibited potent antifungal activities toward the fluconazole-resistant isolate C. albicans 64110, with both having MIC values of 8 µg/mL. In addition, they had significant inhibitory effects toward two Gram-positive bacteria, Staphylococcus aureus UA1758 (compound 31: MIC = 8 µg/mL; compound 42: MIC = 4 µg/mL) and Staphylococcus epidermidis UF843 (compound 31: MIC = 8 µg/mL; compound 42: MIC = 8 µg/mL). The results of an animal experiment indicated that both compounds could improve the survival rate of model mice infected with ATCC 90028 (fluconazole-susceptible isolate). More importantly, the two compounds exhibited notable in vivo effects toward the fluconazole-resistant C. albicans isolate, which is promising with regard to the clinical problem posed by fluconazole-resistant Candida species.

Animal model of dermatophytosis

Dermatophytosis is superficial fungal infection caused by dermatophytes that invade the keratinized tissue of humans and animals. Lesions from dermatophytosis exhibit an inflammatory reaction induced to eliminate the invading fungi by using the host's normal immune function. Many scientists have attempted to establish an experimental animal model to elucidate the pathogenesis of human dermatophytosis and evaluate drug efficacy. However, current animal models have several issues. In the present paper, we surveyed reports about the methodology of the dermatophytosis animal model for tinea corporis, tinea pedis, and tinea unguium and discussed future prospects.

Conazoles

This review provides a historical overview of the analog based drug discovery of miconazole and its congeners, and is focused on marketed azole antifungals bearing the generic suffix “conazole”. The antifungal activity of miconazole, one of the first broad-spectrum antimycotic agents has been mainly restricted to topical applications. The attractive in vitro antifungal spectrum was a starting point to design more potent and especially orally active antifungal agents such as ketoconazole, itraconazole, posaconazole, fluconazole and voriconazole. The chemistry, in vitro and in vivo antifungal activity, pharmacology, and clinical applications of these marketed conazoles has been described.

KP-103, a novel triazole derivative, is effective in preventing relapse and successfully treating experimental interdigital tinea pedis and tinea corporis in guinea pigs

The therapeutic efficacy of KP-103, a triazole derivative, for 10 guinea pigs with interdigital tinea pedis or tinea corporis was investigated. Topical KP-103 solution (0.25 to 1%) was dose-dependently effective in treating both dermatophytoses. A 1% KP-103-treatment rendered all infected skins culture-negative on day-2 posttreatment. A high negative-culture rate was obtained with 1% solutions of butenafine and lanoconazole but not with 1% neticonazole solution. The follow up study performed on day-30 and day-9 posttreatment demonstrated that the relapse rates for 1% KP-103-treated animals with tinea pedis and for those with tinea corporis were 20 and 30%, respectively, and that these values were the same as those for 1% butenafine-treated animals, but lower than those for 1% lanoconazole-treated animals (55 and 80%, respectively). When a single dose of 1% KP-103 was applied to the back skin 48 hr before fungal inoculation, 9 of the 10 animals were protected from the dermatophytosis, suggesting that active KP-103 is retained in skin tissue for at least 48 hr after dosing. Moreover, it was suggested that KP-103 retains a high activity in the horny layer because of its lower keratin-affinity. The effectiveness of KP-103 against dermatophytoses may be due to the favorable pharmacokinetic properties in the skin tissues, together with its potent antifungal activity.

Development of a new medium useful for the recovery of dermatophytes from clinical specimens by minimizing the carryover effect of antifungal agents

Two surface-active compounds, egg lecithin and polysorbate 80, usually used as the deactivators of various preservatives were tested whether they also counteract either or all of the three major topical antifungal drugs, bifonazole (BFZ), lanoconazole (LCZ) and terbinafine (TBF). Both egg lecithin and polysorbate 80, when added to culture media up to final concentrations of 1.0 and 0.7%, respectively, antagonized the anti-dermatophytic activity of the three drugs in a concentration-dependent manner. A greater extent of antagonistic action was exerted when the two deactivators combined at their maximal levels tested were added; MIC's of BFZ were increased more than 30-fold and those of LCZ and TBF more than 200-fold compared with the values obtained in the absence of the deactivators. Using the agar medium supplemented with the combined deactivators, culture studies were carried out with skin tissues specimens taken from guinea pigs whose feet were infected with dermatophytes and subsequently treated with 1% topical preparations of the three antifungal drugs. The experimental data from this animal study demonstrated that the combined deactivators-supplemented medium yielded increased numbers of fungi compared with the basal medium. It looks, therefore, likely that the fungal recovery on the former medium more correctly reflects to actual fungal burden in the infected lesions than the latter. All these results suggest that the combined deactivators-supplemented medium is more useful for mycological evaluation of therapeutic efficacy of imidazole and allylamine drugs against dermatophytoses in both preclinical and clinical studies.

Six novel antimycotics

We have reviewed six new antimycotic agents which have potential applications for human cutaneous and mucosal diseases. Information on these six drugs was obtained via an English language search of PubMed through the US National Library of Medicine. The antimycotic agents reviewed include rilopirox, lanoconazole, NND-502, butenafine, eberconazole and voriconazole. Rilopirox is a synthetic pyridone derivative, related to ciclopirox, with a fungicidal action. Rilopirox is a hydrophobic, topical agent with potential application in mucosal candida infections, tinea versicolor and seborrheic dermatitis. Lanoconazole, an imidazole, is a topical agent with potential application in tinea infections and cutaneous candidiasis. The drug has been available for clinical use in Japan since 1994 and once-daily application to affected areas is recommended. In addition to its antifungal effect, animal data suggest that application of lanoconazole 0.5 or 1% cream is associated with accelerated wound healing. NND-502, a stereoselective analog of lanoconazole, is a topical agent with potential application in tinea pedis infection. NND-502 appears to be more effective in inhibiting ergosterol biosynthesis than lanoconazole or bifonazole and clinical trials comparing these agents are awaited. Butenafine is the first member of a new class of antifungals, the benzylamine derivatives, and has been approved for topical use in Japan (since 1992) and the US. Butenafine has a potent fungicidal action and the drug has been shown to be effective in multiple clinical trials in patients with tinea pedis, tinea corporis and tinea cruris. Butenafine has also been reported to exert an anti-inflammatory action after topical application and this may offer potential benefit over other topical antifungal agents. Eberconazole, an imidazole derivative, is a topical antifungal agent that has been shown to be effective in clinical trials in patients with tinea infections. Preliminary data indicate that the eberconazole is effective against some triazole-resistant yeasts such as Candida krusei and Candida glabrata. Voriconazole is an azole antifungal derivative of fluconazole. The drug is available in both oral and parenteral formulations. Oral voriconazole 200mg twice daily has been effective in treating oropharyngeal candidiasis and apergillosis in immunocompromised patients. After 12 weeks' treatment, a similar dosage of the drug elicited a positive response in 69% of nonimmunocompromised patients with invasive aspergillosis.

In-vitro and in-vivo anti-Trichophyton activity of essential oils by vapour contact

The minimum inhibitory doses (MIDs) of essential oils by vapour contact to inhibit the growth of Trichophyton mentagrophytes and Trichophyton rubrum on agar medium were determined using airtight boxes. Among seven essential oils examined, cinnamon bark oil showed the least MID, followed by lemongrass, thyme and perilla oils. Lavender and tea tree oils showed moderate MID, and citron oil showed the highest MID, being 320 times higher than that of cinnamon bark oil. The MID values were less than the minimum inhibitory concentration (MIC) values determined by agar dilution assay. Furthermore, the minimum agar concentration (MAC) of essential oils absorbed from vapour was determined at the time of MID determination as the second antifungal measure. The MAC value by vapour contact was 1.4 to 4.7 times less than the MAC remaining in the agar at the time of MIC determination by agar dilution assay. Using selected essential oils, the anti-Trichophyton activity by vapour contact was examined in more detail. Lemongrass, thyme and perilla oils killed the conidia, inhibited germination and hyphal elongation at 1-4 micrograms ml-1 air, whereas lavender oil was effective at 40-160 micrograms ml-1 air. The in-vivo efficacy of thyme and perilla oils by vapour contact was shown against an experimental tinea pedis in guinea pigs infected with T. mentagrophytes. These results indicated potent anti-Trichophyton action of essential oils by vapour contact.

Lactoferrin given in food facilitates dermatophytosis cure in guinea pig models

Dermatophytosis is the most common skin infection caused by dermatophytic fungi, such as Trichophyton spp. We studied the in vitro and in vivo antifungal effects of lactoferrin against Trichophyton. Human and bovine lactoferrin, and a bovine lactoferrin-derived peptide, lactoferricin B, showed in vitro antifungal activity that was dependent on the test strain and medium used. In guinea pigs infected on the back with Trichophyton mentagrophytes (i.e. those with tinea corporis), consecutive daily po administration of bovine lactoferrin did not prevent development of symptoms during the early phase of infection, but facilitated clinical improvement of skin lesions after the peak of the symptoms. The fungal burden in lesions was less in guinea pigs that had been given lactoferrin than in untreated controls 21 days after infection. In guinea pigs infected on the foot with T. mentagrophytes (i.e. those with tinea pedis), the fungal burden of the skin on the heel portion of the infected foot 35 days after infection was lower in animals fed lactoferrin than in controls. These results suggest the potential usefulness of lactoferrin as a food component for promoting dermatophytosis cure.

An overview of topical antifungal therapy in dermatomycoses. A North American perspective

Dermatophytes cause fungal infections of keratinised tissues, e.g. skin, hair and nails. The organisms belong to 3 genera, Trichophyton, Epidermophyton and Microsporum. Dermatophytes may be grouped into 3 categories based on host preference and natural habitat. Anthropophilic species predominantly infect humans, geophilic species are soil based and may infect both humans and animals, zoophilic species generally infect non-human mammals. It is important to confirm mycologically the clinical diagnosis of onychomycosis and other tinea infections prior to commencing therapy. The identity of the fungal organism may provide guidance about the appropriateness of a given topical antifungal agent. Special techniques may be required to obtain the best yield of fungal organisms from a given site, especially the scalp and nails. It is also important to realise the limitations of certain diagnostic aids e.g., Wood's light examination is positive in tinea capitis due to M. canis and M. audouinii (ectothrix organisms); however, Wood's light examination is negative in T. tonsurans (endothrix organism). Similarly, it is important to be aware that cicloheximide in culture medium will inhibit growth of non-dermatophytes. Appropriate media are therefore required to evaluate the growth of some significant non-dermatophyte moulds. For tinea infections other than tinea capitis and tinea unguium, topical antifungals may be considered. For effective therapy of tinea capitis an oral antifungal is generally necessary. Similarly, oral antifungals are the therapy of choice, especially if onychomycosis is moderate to severe. Furthermore, where the tinea infection involves a large area, in an immunocompromised host or if infection is recurrent with poor response to topical agents, then oral antifungal therapy may be necessary. Topical antifungal agents may be broadly divided into specific and nonspecific agents. The former group includes the polyenes, azoles, allylamines, amorolfine, ciclopirox and butenafine. Generally the topical agent is available as a cream, sometimes for use intravaginally. Less commonly, the formulation may be in the form of a powder, lacquer, spray, gel or solution. Many of these agents have a broad spectrum of activity, being effective against dermatophytes, yeasts and Malassezia furfur. For the treatment of tinea corporis, tinea cruris tinea versicolor and cutaneous candidosis, once or twice daily application may be required, the most common duration of therapy being 2 to 4 weeks. For tinea pedis the most common treatment duration is 4 to 6 weeks.

In vitro and in vivo antidermatophyte activities of NND-502, a novel optically active imidazole antimycotic agent

In vitro and in vivo antidermatophyte activities of NND-502, a new imidazole antimycotic agent, were compared with those of two existing antifungal agents, lanoconazole and terbinafine. NND-502 exhibited strong in vitro antifungal activity against Trichophyton spp.; its MIC was 1 to 4 times lower than that of lanoconazole or terbinafine. In an in vivo study with a guinea pig model of tinea pedis, 7-day topical treatment with a 0.5% solution of NND-502 (dissolved in polyethylene glycol 400) was more effective than that with a 0.5% solution of either lanoconazole or terbinafine for eradicating fungi from the infected feet. When the duration of treatment was shortened to 3 days, a topical 1% solution of NND-502 achieved a complete mycological cure, while topical 1% solutions of lanoconazole and terbinafine did not.