Tolciclate

The in vitro antifungal susceptibilities of six clinical Trichophyton rubrum isolates obtained sequentially from a single onychomycosis patient who failed oral terbinafine therapy (250 mg/day for 24 weeks) were determined by broth microdilution and macrodilution methodologies. Strain relatedness was examined by random amplified polymorphic DNA (RAPD) analyses. Data obtained from both broth micro- and macrodilution assays were in agreement and revealed that the six clinical isolates had greatly reduced susceptibilities to terbinafine. The MICs of terbinafine for these strains were >4 μg/ml, whereas they were <0.0002 μg/ml for the susceptible reference strains. Consistent with these findings, the minimum fungicidal concentrations (MFCs) of terbinafine for all six strains were >128 μg/ml, whereas they were 0.0002 μg/ml for the reference strain. The MIC of terbinafine for the baseline strain (cultured at the initial screening visit and before therapy was started) was already 4,000-fold higher than normal, suggesting that this is a case of primary resistance to terbinafine. The results obtained by the broth macrodilution procedure revealed that the terbinafine MICs and MFCs for sequential isolates apparently increased during the course of therapy. RAPD analyses did not reveal any differences between the isolates. The terbinafine-resistant isolates exhibited normal susceptibilities to clinically available antimycotics including itraconazole, fluconazole, and griseofulvin. However, these isolates were fully cross resistant to several other known squalene epoxidase inhibitors, including naftifine, butenafine, tolnaftate, and tolciclate, suggesting a target-specific mechanism of resistance. This is the first confirmed report of terbinafine resistance in dermatophytes.

The fungicidal activities of thiocarbamate antifungal agent liranaftate were studied by determining the MIC and the MCC against Trichophyton rubrum with the Milliflex -100 Test System and by determining the time-kill curve in comparison to that of six reference agents. Liranaftate and lanoconazole both showed excellent fungistatic activity against the conidia of T. rubrum. For each of these agents, the MIC after 14 days of contact was 0.009 g/ml. The liranaftate-induced decrease in the MCC occurred from 9 days onwards; MCC at 14 days was 0.039 g/ml. The MCC for tolciclate was also reduced from 9 days onwards, but that of amorolfine, lanoconazole, neticonazole, clotrimazole and bifonazole was not lowered up to 14 days. Similar results were obtained when the studies were performed with germinated conidia. The time-kill curves showed that both liranaftate and tolciclate, at concentrations ranging from 2 to 32 times the MICs, achieved a decrease in viable counts to below the detection limit within 7 to 9 days. In experiments with low levels of inoculum, only amorolfine produced a decrease to below the detection level, and that occurred at 14 days; no reduction in viable counts was observed up to 14 days with the four azole agents. Our data suggest that antifungal agents of the thiocarbamate class possess the most potent fungicidal activity against dermatophytes; these are followed in order by morpholine and azole antifungals.