Photodynamic therapy can help combat secondary infections in COVID-19 patients, according to researchers at the Optics and Photonics Research Center (CEPOF), which is supported by the São Paulo Research Foundation. The researchers advocate photodynamic therapy as a complementary treatment for decreasing the viral and bacterial load in the patient’s respiratory tract. The compounds used in photodynamic therapy interact with light to produce singlet oxygen, a highly reactive oxygen species that kills viruses and bacteria by oxidizing their membranes. “When the patient inhales these substances, the drug can be activated with extracorporeal light, which then attacks pathogens in the airways,” principal investigator Vanderlei Bagnato said. Use of photodynamic therapy, which combines light and a photosensitizing chemical substance to kill microorganisms in the respiratory tract, could serve as a complementary treatment to combat secondary infections in COVID-19 patients. Courtesy of CEPOF. The researchers said that opportunistic pathogens propagate mainly through the upper respiratory tract owing to natural colonization of the oropharynx, and that photodynamic therapy could help reduce the number of these microorganisms present in the oropharynx and prevent their penetration into the mucosal barrier, and hence their proliferation. Since photodynamic therapy only eliminates harmful microorganisms present in the airways and not in the bloodstream, it cannot be used to attack the novel coronavirus SARS-CoV-2 directly. However, the researchers believe that the development of techniques to combat COVID-19 coinfections caused by bacteria and other viruses could help patients avoid the need for intensive care and minimize disease transmission. “COVID-19 can lead to complications that go beyond the virus, and we should also strive to find treatments for these other problems,” Bagnato said. “Treating coinfections and secondary infections can improve the prognosis in severe cases, above all for patients who are intubated and face a higher risk of infection by other microorganisms such as the bacteria that cause pneumonia.” CEPOF has conducted several studies on the use of photodynamic therapy to treat pneumonia, skin cancer, and other diseases. “We’re about to begin a study to evaluate the use of photodynamic therapy in cases of pneumonia in pigs. This stage precedes clinical trials in humans,” Bagnato said. The study will be conducted by CEPOF in partnership with researchers at the University of Toronto. “We hope it will be fast-tracked because, although we don’t know for sure yet, it’s quite likely that people who survive COVID-19 may be more prone to respiratory complications such as pneumonia because of the severe inflammation,” Bagnato said. “We need to develop novel techniques and alternative treatments.” The research was published in Photodiagnosis and Photodynamic Therapy (www.doi.org/10.1016/j.pdpdt.2020.101804).