Fig. 1

Isobolograms representing in vitro interactions of lycorine and pretazettine. The compounds were combined in fixed ration generating solutions which were tested for their cytotoxicity in BHK-21 (a) and Vero (c) cells and in parallel for their antiviral activity against DENV-2 (b) and ZIKV (d). The pair of doses were evaluated at the level of EC₅₀ and CC₅₀, which were determined by regression curves. Subsequently, their FIC was determined and plotted on the graphs above. All points on isobole represent dose pairs, FIC of pretazettine (x-axis) and lycorine (y-axis), that are expected to give the EC₅₀ (in the case of viruses) or CC₅₀ (in the case of cells). Plots are observed very close to the theoretical diagonal line, which means, in short, the indifferent effect of both compounds used together. The illustration strengthens the results obtained of statistical analyses, from which the fractional inhibitory concentration index (FICI) was obtained (shown at the upper right corner) and used to define interactions as indifferent for being between 0.5 and 4