In December 2019, the Wuhan Municipal Health Committee identified an outbreak of viral pneumonia cases of unknown cause. Coronavirus RNA was quickly identified in these patients. This novel coronavirus has been designated SARS-CoV-2, and the disease caused by this virus has been designated COVID-19 and has infected hundreds of thousands of confirmed individuals in more than 200 countries. Currently there are no approved therapeutic agents available for coronaviruses. There is an urgent need for an effective treatment to treat symptomatic patients but also to decrease the duration of virus transmission in the community. Among candidate drugs to treat COVID-19, repurposing of FDA-approved drugs for use as antiviral treatments is proposed because knowledge on safety profile, side effects, and drug interactions are well known.
In silico screening of FDA licensed compound libraries against the SARS CoV 2 protease Plpro catalytic site was performed using solved crystal structures of the protein. Plpro (Papain-like protease) is an early acting protease responsible for initial processing of the SARS CoV2 polyprotein into active subunits. Plpro also has ubiquitinase activity, and is implicated in early infection phase inhibition of innate (interferon) immune responses which otherwise would suppress viral replication. A ranked list of licensed compounds with predicted binding activity in the Plpro catalytic site was computationally generated, and the Plpro catalytic site binding pose of each of the top compounds was examined and ranked by a team of pharmaceutical chemists. Package inserts or product monographs for the licensed compounds which generated high computational binding scores and passed inspection were then reviewed and used to rank compounds based on adverse events, warnings, drug interactions on-target mechanisms, pharmacokinetic and absorption, metabolism, excretion and toxicity (ADMET), protein binding and available therapeutic window considerations. Famotidine (Pepcid), a histamine H2 antagonist widely available over-the-counter, was repeatedly computationally scored among the highest of the compounds tested, and was associated with the most favorable pharmacokinetic and safety profile. A series of analogs of famotidine were generated using PubChem, and many of these scored even higher as potential candidates. This control compound set further confirmed the predicted binding of the molecular backbone chemotype at the Plpro protease/ubiquitinase site. Currently available as oral and IV products, famotidine has a very attractive proven safety, drug interaction, and therapeutic window profile. Samples of famotidine have been submitted at Southern Research and IITRI for in vitro testing in COVID-19 cultures. Unpublished anecdotal case studies suggest clinical benefits associated with administration of famotidine 40 mg PO TID in mild COVID-19 infection.
On 29 April 2020, the National Institute of Allergy and Infectious Diseases (NIAID) announced that Remdesivir was better than placebo in reducing time to recovery for people hospitalized with advanced COVID-19 and lung involvement. In an earlier study of adult patients admitted to a hospital for severe COVID-19, Remdesivir was not associated with statistically significant clinical benefits. In that study, Remdesivir was not associated with a difference in time to clinical improvement. Although not statistically significant, patients receiving Remdesivir had a numerically faster time to clinical improvement than those receiving placebo among patients with symptom duration of 10 days or less. Remdesivir was stopped early because of higher numbers of adverse events compared to placebo. Because of these studies the FDA stated on 1 May 2020, that it is "reasonable to believe" that known and potential benefits of Remdesivir outweigh its known and potential risks, in some specific populations hospitalized with severe COVID-19.
Given the refinement of standard of care to include Remdesivir and no longer hydroxychloroquine, we have edited the study protocol to reflect this new standard of care.
