Use of decimal assay for additivity to demonstrate synergy in pair combinations of econazole, nikkomycin Z, and ibuprofen against Candida albicans in vitro

Abstract

Interactions between six compounds (econazole, miconazole, amphotericin B, nystatin, nikkomycin Z, and ibuprofen) were investigated for their antifungal activities against Candida albicans by using pair combinations in an in vitro decimal assay for additivity based on disk diffusion. Additive interactions were observed between miconazole and econazole, amphotericin B and nystatin, and amphotericin B and ibuprofen, while an antagonistic interaction was observed between econazole and amphotericin B. Synergistic interactions were recorded for the combinations of econazole and ibuprofen, econazole and nikkomycin Z, and ibuprofen and nikkomycin Z.Candida albicans is an opportunistic fungal pathogen responsible for causing candidiasis in individuals with an underlying pathological process or deficiency state. Increases in the numbers of immunocompromised individuals have resulted in concomitant increases in the occurrence of Candida infections (9). For more than two decades the fungicidal polyene compounds, such as amphotericin B and nystatin, provided the most effective treatment of candidiasis, despite their potential toxicity to humans. More recently, the azole antifungal compounds have emerged as the principal drugs used in the treatment of candidiasis, although their activities are fungistatic rather than fungicidal (2). Improvements in the efficacy of antifungal drug therapy and reductions in toxicity may be achieved by using combinations of drugs. To date there have been few investigations of the interactions between antifungal agents (1,3,4,(6)(7)(8).One of the limitations to such studies on the evaluation of antifungal activity has been the lack of an adequate in vitro methodology capable of yielding reproducible results. Sanders et al. (11) pointed out the inherent methodologic limitations of the two most widely used methods for assessing drug interactions, namely, the time-kill technique and the checkerboard titration, and went on to describe a new in vitro test for antibacterial agents designed to avoid many of the problems previously described (11). This new test, the decimal assay for additivity (DAA), was based on the disk diffusion assay and was designed to have a precisely defined endpoint for additivity so that interactions greater or less than additivity (i.e., synergism or antagonism, respectively) could be accurately identified. The DAA involves initially performing disk diffusion assays with each antibiotic on its own over a range of drug masses in order to obtain a standard dose-response curve. A target zone of inhibition for each drug combination, representing a zone in the midrange of the standard curve for each drug, is selected so that increases or decreases in zones of inhibition resulting from drug interactions can be reliably detected. The mass of each drug on its own required to produce this target zone (i.e., the biologic equivalence factor [BEF]) is calculated by using the linear regression equation for the standard doseresponse curve. Once the two BEFs for a combination of a pair of d...

Evaluation of the best method to assess antibiotic potentiation by phytochemicals against Staphylococcus aureus

“…Also, methods for the interpretation of kill-kinetic studies vary, and synergy has been defined by some authors as at least a 100-fold increase in killing at 24 h (Bonapace et al, 2000;Jung et al, 2004;Kiraz et al, 2009;Mayer and Nagy, 1999), while other authors consider a 200-fold increase (Guo et al, 2008;Leonard, 2012;Tan et al, 2011). Relatively to checkerboard, the endpoint (i.e., the complete inhibition of growth) is a qualitative measure (Tariq et al, 1995), and the occurrence of synergy appears to be highly dependent on the method of interpretation (Bonapace et al, 2002). Also, the reproducibility of checkerboard is hardly the best.…”

In Vitro Efficacy of Nikkomycin Z against the Human Isolate of the Microsporidian Species Encephalitozoon hellem

“…However, a more extensive study of the drug kinetics and of other strains of the same and other related species (Encephalitozoon cuniculi, Encephalitozoon intestinalis) is required. Our results also indicate the need to test this drug on these protozoa in combination with other chemotherapeutic agents, namely, azole derivatives, on the basis of recent successfully performed studies against some chitinous fungi (1,14,20).…”

In vitro activities of antifungal agents alone and in combination against fluconazole-susceptible and -resistant strains of Candida dubliniensis

“…3,16 Here, combinations of amphotericin B and azoles mostly resulted in indifferent interactions against C. dubliniensis in both groups of isolates.…”

“…most commonly evaluated in the majority of in vitro antifungal combination studies. While the combination of azoles with amphotericin B has provided controversial results, 3 most of studies have found additive or synergistic effect when azoles were combined with terbinafine against C. albicans. [4][5][6] Other Candida spp.…”