An update on clinical photodynamic therapy for fighting respiratory tract infections: a promising tool against COVID-19 and its co-infections

Recently coronavirus infection 2019 (COVID-19) was declared as a Public Health Emergency by the World Health Organization. Extensive measures to reduce person-to-person transmission of COVID-19 and scientific research have been developed aiming to combat it. The idealization of vaccines will be of great help, but they will have to be constantly redone due to the high frequency of mutation of the virus. Also, it is necessary to develop techniques that allow to combat viral, bacterial and fungi load. In this sense, photodynamic therapy can be an alternative and efficient tool against viruses, bacteria, and fungi in the respiratory tract. The photodynamic therapy protocol is characterized by activation of a photosensitizer using an appropriate light source that in the presence of molecular oxygen is able to damage microorganisms. Herein, we review the past 25 years (1995-2019) concerning the use of photodynamic therapy in clinical trial against respiratory tract infections. We did not intend to create a comprehensive review; instead we highlight some the most important aspects for this infection to connect with the possibility of inactivation of the SARS-CoV-2 and its co-infections by photo reaction. We emphasize the use of photodynamic therapy as a potential clinical tool to decrease the microbial load in the respiratory tract, showing its main applications, advantages, and limitations.