At a time when antibiotic resistance is growing and some bacterial infections of the skin are getting harder to treat, the idea of the antiseptic is still somewhat attractive. Antiseptics are substances that generally have a physical-chemical action against microbes – usually directed towards the cell wall or its associated proteins. For some skin infections, antiseptics are potentially appropriate as they have no little systemic side-effects and have a rapid action against microbes with a vanishingly low rate of resistance arising from their use.
I remember being told by a dermatologist that the imidazole group of antifungal drugs, as well as being effective for tinea pedis also have anti-bacterial properties, particularly against Gram positive organisms. Following this, I located a paper to this effect which was published in 1982 (1) using clotrimazole, although earlier work from the 1970’s had also made this observation.
So, antifungals such as miconazole, clotrimazole and econazole could potentially be used for treating skin infections? This 1981 paper highlighted the benefits of clotrimazole against a small range of gram-negative bacteria. The author concluded that the inclusion of lactic acid may serve to augment gram-negative coverage as well. Since then although further work has appeared this discovery has not really been seen in practice.
This year, in the German journal “Mycoses” (August edition), Nenoff and colleagues (2) published a paper which revisited this property of the azoles running a battery of tests using miconazole. To do this they isolated a range of both Gram-negative and Gram-positive bacteria and exposed them to differing concentrations of the drug to observe its effects. The object of the study being to identify the minimum amount of the drug required to have an antibacterial effect known as the minimum inhibitory concentration (or MIC for short).
The study demonstrated that miconazole, even at relatively low concentrations, can inhibit Staphylococcus aureus (including methicillin resistant and sensitive strains as well as Fucidin resistant strains [FRSA]) as well as Streptococcal species including pyogenes as well as Enterococcus and Corynebacterium. The main conclusion is that this drug could be used topically (at its current over-the-counter concentration) but will need further testing as essentially applying it to the skin (in vivo) is different to testing it in a lab (in vitro) as the environment (different pH, temperature etc.,) may reduce the effects of the drug when used topically.
For podiatry, what does this mean? Well, I have been using it successfully for erythrasma for many years, which is an over-growth of the skin natural flora found in the webs spaces as maceration and malodour. Treating the condition is worthwhile as topical azoles are cheap but also the condition untreated can lead to skin breakage and potentially secondary infection and cellulitis. Encouraging patients to use it as part of their foot care regime is a good idea as it can cover the more common tinea pedis as well. The drug is cheap and has an excellent safety profile but remember, from my earlier blog, that patients on warfarin should not use miconazole – even topically following an MHRA warning.
References
1. Schaller K. In vitro antibacterial activity of different clotrimazole formulations. Chemotherapy. 1982;28 Suppl 1:32-6.
2. Nenoff P, Koch D, Krüger C, Drechsel C, Mayser P. New insights on the antibacterial efficacy of miconazole in vitro. Mycoses. 2017;60(8):552-7.