Experimental and Conformational Analyses of Interactions between Butenafine and Lipids

Abstract

Butenafine (N-4-tert-butylbenzyl-N-methyl-1-naphtalenemethylamine hydrochloride) is an antifungal agent of the benzylamine class that has excellent therapeutic efficacy and a remarkably long duration of action when applied topically to treat various mycoses. Given the lipophilic nature of the molecule, efficacy may be related to an interaction with cell membrane phospholipids and permeabilization of the fungal cell wall. Similarly, high lipophilicity could account for the long duration of action, since fixation to lipids in cutaneous tissues might allow them to act as local depots for slow release of the drug. We have therefore used computer-assisted conformational analysis to investigate the interaction of butenafine with lipids and extended these observations with experimental studies in vitro using liposomes. Conformational analysis of mixed monolayers of phospholipids with the neutral and protonated forms of butenafine highlighted a possible interaction with both the hydrophilic and hydrophobic domains of membrane phospholipids. Studies using liposomes demonstrated that butenafine increases membrane fluidity [assessed by fluorescence polarization of 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene and 1,6-diphenylhexatriene] and membrane permeability (studied by release of calcein from liposomes). The results show, therefore, that butenafine readily interacts with lipids and is incorporated into membrane phospholipids. These findings may help explain the excellent antifungal efficacy and long duration of action of this drug when it is used as a topical antifungal agent in humans.Butenafine (N-4-tert-butylbenzyl-N-methyl-1-naphtalenemethylamine hydrochloride), a broad-spectrum topical antifungal agent (21), shows excellent therapeutic efficacy in humans with dermatomycoses (13,22,34,36,44,50,54). In vitro, the MIC and the minimal fungicidal concentration of butenafine against Trichophyton mentagrophytes and Microsporum canis were 0.012 to 0.05 mg/liter, i.e., 4 to 130 times lower than those for naftifine, tolnaftate, clotrimazole, and bifonazole (13, 36), other well-known antifungal drugs. Of additional interest is the fact that, in contrast to imidazole and triazole antifungals, butenafine does not interact with cytochrome P450-dependent enzymes (13) and is, therefore, unlikely to cause toxicity via untoward drug-drug interactions.The efficacy of butenafine might be attributed to its ability to inhibit sterol synthesis by blocking squalene epoxidation (24,25). This would lead to depletion of ergosterol, an essential lipid component of the fungal membrane; accumulation of squalene; and alteration in membrane function. At high concentrations, the damaging effect of butenafine on the cell membrane might play a major role in its anticandidal activity (27).One of the major characteristics of butenafine is its ability to provide long-lasting antifungal activity. Topical application of butenafine produces residual fungicidal concentrations in the skin (and particularly in the stratum corneum) that remain for...

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