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• Acute respiratory distress syndrome, sepsis and thromboinflammation may complicate COVID-19-associated critical illness. • The efficacy of extracorporeal blood purification therapies in COVID-19 remains questionable. • Concerns exist regarding the safety and immunosuppressive effects of therapeutic plasma exchange. • Plasma exchange pilot studies showed promise in the treatment of complex life-threatening COVID-19. COVID-19 (coronavirus disease 2019), caused by the novel coronavirus SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), emerged in Wuhan, China, and has spread worldwide, resulting in over 73 million cases and more than 1 600 000 deaths as of December 2020. Although the disease is asymptomatic in most cases, some patients develop life-threatening disease characterised by acute respiratory distress syndrome, sepsis, multisystem organ failure (MSOF), extrapulmonary manifestations, thromboembolic disease and associated cytokine release syndrome. The rationale for applying therapeutic plasma exchange (TPE) early in the course of fulminant COVID-19 is the suppression of thromboinflammation and amelioration of microangiopathy, thus preventing the ensuing MSOF. In the course of complicated critical illness due to COVID-19, immune dysregulation may be as important as viral replication itself. Moreover, the natural course of SARS-CoV-2 infection remains obscure, as re-infections and/or recurrently positive real-time PCR results have been reported. Although concerns still exist regarding its potential immunosuppressive effects and safety, TPE shows promise in the management of life-threatening COVID-19 as documented by various pilot studies, which remain to be confirmed by future randomised controlled trials. However, current data suggest that TPE could be an adjunctive rescue therapy in complex COVID-19 critical illness. [ABSTRACT FROM AUTHOR]

• Chloroquine (CQ) has diverse modes of action against viral infections. • CQ may interfere with SARS-CoV-2 attachment to the host ACE2 receptor. • CQ may hamper the STING pathway to attenuate the pro-inflammatory response. • Hydroxychloroquine (HCQ) might be a logical approach in the treatment of SARS-CoV-2 infection. • Large clinical trials are needed before clinical recommendations of HCQ against COVID-19. Chloroquine (CQ) and its analogue hydroxychloroquine (HCQ) have long been used worldwide as frontline drugs for the treatment and prophylaxis of human malaria. Since the first reported cases in Wuhan, China, in late December 2019, humans have been under threat from coronavirus disease 2019 (COVID-19) caused by the novel coronavirus SARS-CoV-2 (previously known as 2019-nCoV), subsequently declared a pandemic. While the world is searching for expedited approval for a vaccine, which may be only preventative and not a cure, physicians and country leaders are considering several concerted clinical trials suggesting that the age-old antimalarial drugs CQ/HCQ could be a potent therapeutic against COVID-19. Based on accumulating scientific reports, here we highlight the possible modes of action of CQ/HCQ that could justify its use against viral infections. Considering the global health crisis of the COVID-19 pandemic, the option of repurposing old drugs, e.g. CQ/HCQ, particularly HCQ, for the treatment of SARS-CoV-2 infection could be a good choice. CQ/HCQ has diverse modes of action, including alteration of the acidic environment inside lysosomes and late endosomes, preventing endocytosis, exosome release and phagolysosomal fusion, and inhibition of the host cytokine storm. One or more diverse mechanisms might work against viral infections and reduce mortality. As there is no cure for COVID-19, clinical testing of HCQ is urgently required to determine its potency against SARS-CoV-2, as this is the currently available treatment option. There remains a need to find other innovative drug candidates as possible candidates to enter clinical evaluation and testing. [ABSTRACT FROM AUTHOR]

• Pathogenesis of cytokine release syndrome (CRS) in severe COVID-19 patients. • Key role of interleukin-6 (IL-6) in CRS. • IL-6 receptor (IL-6R) antagonist tocilizumab suggested as a possible drug for severe COVID-19. Since December 2019, a viral pneumonia, named coronavirus disease 2019 (COVID-19), from Wuhan, China, has swept the world. Although the case fatality rate is not high, the number of people infected is large and there is still a large number of patients dying. With the collation and publication of more and more clinical data, a large number of data suggest that there are mild or severe cytokine storms in severe patients, which is an important cause of death. Therefore, treatment of the cytokine storm has become an important part of rescuing severe COVID-19 patients. Interleukin-6 (IL-6) plays an important role in cytokine release syndrome. If it is possible to block the signal transduction pathway of IL-6, it is expected to become a new method for the treatment of severe COVID-19 patients. Tocilizumab is an IL-6 receptor (IL-6R) blocker that can effectively block the IL-6 signal transduction pathway and thus is likely to become an effective drug for patients with severe COVID-19. [ABSTRACT FROM AUTHOR]