Inhalable spray-dried dry powders combining ivermectin and niclosamide to inhibit SARS-CoV-2 infection in vitro

SARS-CoV-2, the virus responsible for the COVID-19 pandemic, predominantly affects the respiratory tract, underscoring the need to develop antiviral agents in an inhalable formulation that can be delivered as prophylactic and/or therapeutic drugs directly to the infection site. Since the beginning of the pandemic, our group has been exploring the possibility of developing combinations of antiviral drugs that can be delivered as inhalable therapy, including combinations of remdesivir and ebselen or remdesivir and disulfiram prepared using a spray-drying technique. In this study, we used a similar spray-drying technique to develop inhalable dry powders combining the controversial drugs ivermectin and niclosamide, which have been reported to exhibit synergistic activity against SARS-CoV-2 in vitro. The combined dry powders were within the size range of 1-5 μm, amorphous in nature and displayed characteristic morphology after spray drying. The emitted dose (ED) of the spray-dried powders ranged from 68 to 83 %, whereas the fine particle fraction (FPF) ranged between 50 and 74 %. All the prepared dry powders remained stable under different humidity conditions (<15 % RH and 53 % RH). Interestingly, the optimized combinational dry powder of ivermectin and niclosamide showed an improved cytotoxic profile (CC₅₀ value of 45.99 µM) and enhanced anti-SARS-CoV-2 activity in vitro (EC₅₀ of 2.67 µM) compared to the single dry powders of ivermectin (CC₅₀ = 20.25 µM and EC₅₀ = 8.61 µM) and niclosamide (CC₅₀ = 21.36 µM and EC₅₀ = 5.28 µM). In summary, we developed a stable and inhalable combinational dry powder containing ivermectin and niclosamide, capable of inhibiting SARS-CoV-2 replication in vitro, demonstrating the potential to prepare dry powders that could be developed and delivered as inhalable antiviral drugs to prevent and/or treat SARS-CoV-2 or similar respiratory viruses.