Repositioning chloroquine as antiviral prophylaxis against COVID-19: potential and challenges

The Coronavirus Disease 2019 (COVID-19) pandemic is advancing globally, and pharmaceutical prophylaxis is one solution. Here, we propose repositioning chloroquine (CQ) as prophylaxis against COVID-19. CQ blocks viral attachment and entry to host cells and demonstrates efficacy against a variety of viruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of COVID-19. Furthermore, CQ is safe, inexpensive, and available. Here, we review the antiviral mechanisms of CQ, its in vitro activity against coronaviruses, its pharmacokinetics (PK) and adverse effects, and why it could be more efficacious as a prophylactic rather than as a therapeutic, given the infection dynamics of SARS-CoV-2. We propose two prophylactic regimens based on efficacy and risk considerations. Although it is largely preclinical data that suggest the potential of CQ, properly planned prophylactic trials and further research are urgently needed.