Remdesivir-ivermectin combination displays synergistic interaction with improved in vitro activity against SARS-CoV-2

Abstract

A key element for the prevention and management of coronavirus disease 2019 is the development of effective therapeutics. Drug combination strategies offer several advantages over monotherapies. They have the potential to achieve greater efficacy, to increase the therapeutic index of drugs and to reduce the emergence of drug resistance. We assessed the in vitro synergistic interaction between remdesivir and ivermectin, both approved by the US Food and Drug Administration, and demonstrated enhanced antiviral activity against severe acute respiratory syndrome coronavirus-2. Whilst the in vitro synergistic activity reported here does not support the clinical application of this combination treatment strategy due to insufficient exposure of ivermectin in vivo, the data do warrant further investigation. Efforts to define the mechanisms underpinning the observed synergistic action could lead to the development of novel treatment strategies.

Keywords: COVID-19; CPE; Combination therapy; Cytopathic activity; SARS-CoV-2; Synergy.

Fig. 1

Concentration–effect relationship for the inhibition (%) of severe acute respiratory syndrome coronavirus-2 cytopathic activity for remdesivir and ivermectin. For each compound, activity was expressed relative to uninfected/untreated controls (100% inhibition of viral cytopathic activity) and infected/untreated controls (0% inhibition of viral activity). For each compound, activity was assessed at 25.00 µM, 8.33 µM, 2.78 µM, 0.93 µM, 0.31 µM, 0.10 µM and 0.03 µM in triplicate. Data points impacted by drug toxicity were removed automatically. Non-linear regression using an E_max model was performed on data taken from three independent biological replicates in order to generate concentration–effect predictions (solid black lines). For each compound, half maximal effective concentration (EC₅₀) values, hillslope and replicate number (n) are shown. Dashed lines represent EC₅₀ of each compound. Squares, diamonds and circles represent individual biological replicates, and error bars represent standard deviation calculated from technical triplicates.

Fig. 2

Ivermectin and remdesivir display synergistic interaction. (A) Using half maximal effective concentration (EC₅₀) values, ranges of ivermectin and remdesivir were analysed for synergy. Data are presented for fixed concentrations at 25 µM (corresponding to 1.0), 20 µM (0.8), 15 µM (0.6), 10 µM (0.4) and 5 µM (0.2). The area indicating synergy [fractional inhibitory concentration (FIC) ≤0.5] is shown in grey. Squares, diamonds and circles represent individual biological replicates, each derived from technical triplicates. (B) Three-dimensional (3D) visualization of compound integration based on the highest single agent (HSA) synergy score (left) alongside heatmap showing compound combination dose–response matrices (right). 3D visualizations and matrices are shown for individual biological replicates, each derived from technical triplicates.