Laboratory Techniques Alternative to In Vivo Experiments for Studying the Liberation, Penetration and Fungicidal Action of Topical Antimycotic Agents in the Skin, Including Ciclopiroxolamine

Abstract

Summary: Short‐term experiments on excised skin (human, pig) gave the following results: 1. In the tissue activity test with direct inoculation (D‐TAT) commercial preparations of the non‐azole antimycotics ciclopiroxolamine, tolnaftate and naftifine, produced higher inhibitory activity against Trichophyton mentagrophytes (standard strain) in various levels of the horny layer than were produced by the azole antimycotics econazole, miconazole, clotrimazole, oxiconazole and bifonazole. Fast drying solutions of antimycotics invariably gave higher inhibitory activities than creams. In the ultrafiltration tissue activity test (UFT‐ TAT) against Candida albicans (2 strains), antimycotic agents ranked in order of effectiveness as follows: ciclopiroxolamine – most of the azole antimycotics – bifonazole and naftifine. 2. In tests of fungicidal activity against T. mentagrophytes (2 strains) and Microsporum gypseum (1 strain) the first step was to inoculate the skin surface. After the horny layer had been penetrated by fungal mycelia, antimycotic agents of documented fungicidal potency, chiefly in the form of creams, were applied to the skin surface and left to act for up to 18 hours. The horny layer and epidermis were then scraped off and the concentration of viable fungi was determined. Ciclopiroxolamine cream and lotion produced by far the greatest diminution in viable fungi; creams containing oxiconazole and naftifine were moderately effective and those containing tioconazole and bifonazole produced a relatively small decrease in viable fungi. To avoid erroneous results it is important to homogenize and dilute the skin scrapings; if this is not done certain antimycotics will give misleadingly high fungal killing rates. At this early stage the scatter of results is still wide and minor differences in efficacy cannot as yet be detected with certainty. 3. From the results of various comparative tests it is evident that pig skin can be used as a substitute for human skin in the tests listed under 1. and 2. above. This discovery may make a valuable contribution towards limiting the need for experiments on living animals and trials on human beings. Zusammenfassung: In Kurzzeitversuchen an exzidierter Haut (Mensch, Schwein) wurde gefunden: 1. Im Gewebeaktivitätstest mit direkter Inokulation (D‐GAT) wurde mit Handelspräparaten der Nichtazol‐Antimykotika Ciclopiroxolamin, Tolnaftat und Naftifin in verschiedenen Hornschichtniveaus eine höhere Hemmaktivität gegenüber Trichophyton mentagrophytes (Standard‐Stamm) erzielt als mit solchen der Azol‐Antimykotika Econazol, Miconazol, Clotrimazol, Oxiconazol und Bifonazol. Rasch trocknende Lösungen von Antimykotika ergaben durchweg höhere Hemmaktivitäten als Cremes. Im Ultrafiltrations‐Gewebeaktivitätstest (UFT‐GAT) gegenüber Candida albicans (2 Stämme) ergab sich nach erzielter Wirksamkeit die Rangfolge Ciclopiroxolamine – Mehrzahl der Azolantimykotika – Bifonazol und Naftifin. 2. In Fungizidie‐Testen gegenüber T. mentagrophytes (2 Stämme) und Microsporum gypseum (1 Stamm) wurde zunächs...

Experimental Models in Predicting Topical Antifungal Efficacy: Practical Aspects and Challenges

“…Their data are also a good prediction of the 'effective concentration' of the antifungal formulations, which each have varying potencies and penetrating powers. Using the same testing methods on pig skin as Dittmar and Jovic [16] , Hanel et al [44] found in 1988 that ciclopiroxolamine has a higher fungicidal activity than bifonazole because of its greater ability to penetrate the stratum corneum and enter deeply into the stratum granulosum, which further emphasizes the importance of skin permeation in antifungal efficacy as well the success in using pig skin to study penetration kinetics. Testing topical antifungals may begin with finding MICs, but once again, comparison of MIC values alone will not differentiate between the two antifungals in question; in vitro studies need to be coupled with animal membrane models, such as pig skin models, before moving onto in vivo studies.…”

“…Dittmar and Jovic [16] find that excised pig skin is a suitable substitute for human skin in showing antimycotic efficacy in direct tissue activity tests and ultrafiltration tissue activity tests against pathogenic fungi. Pig stratum corneum and human stratum corneum share an extraordinarily similar penetration of ciclopiroxolamine as measured by percentage inhibition of T. mentagrophytes in the upper, middle and deep layers of the horny layer.…”

“…(1) Guinea pig stratum corneum resembles human stratum corneum in thickness [4] (2) Versatile [4] (1) There are inconsistencies in the lipid composition permeation qualities between anatomical sites of the animal [4] (2) Skin is fragile and usually more permeable than human skin [15] (3) Skin lacks pronounced hornification of human skin which affects permeation studies [16] The best 'natural' model membrane (1) Pig stratum corneum is similar in thickness to human stratum corneum (2) Similar permeability properties to human skin (3) Easy to acquire from slaughterhouses (1) Has a different lipid content than that of human stratum corneum 4…”