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Despite the success of vaccines and selected repurposed treatments, COVID-19 is likely to remain a global health problem and further chemotherapeutics are required. Many repurposed drugs have progressed rapidly to Phase 2 and 3 trials without characterisation of Pharmacokinetics (PK)/Pharmacodynamics (PD) including safety in COVID-19. One such drug is Nafamostat Mesylate (Nafamostat), a synthetic serine protease inhibitor with anticoagulant and anti-inflammatory properties. Preclinical data has demonstrated that it is has potent antiviral activity against SARS-CoV-2 by directly inhibiting the transmembrane protease serine 2 (TMPRSS2) dependent stage of host cell entry.MethodsWe present the findings of a phase Ib/II open label, platform randomised controlled trial (RCT), exploring the safety of intravenous Nafamostat in hospitalised patients with confirmed COVID-19 pneumonitis. Patients were assigned randomly to standard of care (SoC), Nafamostat or an alternative therapy. Secondary endpoints included clinical endpoints such as number of oxygen free days and clinical improvement/ deterioration, PK/PD, thromboelastometry, D Dimers, cytokines, immune cell flow cytometry and viral load.ResultsData is reported from 42 patients, 21 of which were randomly assigned to receive intravenous Nafamostat. The Nafamostat group developed significantly higher plasma creatinine levels, more adverse events and a lower number of oxygen free days. There were no other statistically significant differences in the primary or secondary endpoints between Nafamostat and SoC. PK data demonstrated that intravenous Nafamostat was rapidly broken down to inactive metabolites. We observed an antifibrinolytic profile, and no significant anticoagulant effects in thromboelastometry. Participants in the Nafamostat group had higher D Dimers compared to SoC. There were no differences in cytokine profile and immune cell phenotype and viral loads between the groups.ConclusionIn hospitalised patients with COVID-19, we did not observe evidence of anti-inflammatory, anticoagulant or antiviral activity with intravenous Nafamostat. Given the number of negative trials with repurposed drugs, our experimental medicine trial highlights the value of PK/PD studies prior to selecting drugs for efficacy trials. Given the mechanism of action, further evaluation of Nafamostat delivered via a different route may be warranted. This trial demonstrates the importance of experimental trials in new disease entities such as COVID-19 prior to selecting drugs for larger trials.

Spontaneous beating rate was studied in mouse isolated atrial preparations and in guinea-pig single myocytes isolated from the sinus node (SAN) region of the heart. In atrial preparations, the I(f) blockers ZD7288 (1 μM) and ivabradine (3 μM) both reduced spontaneous beating rate by more than 200 bpm, and the change in beating rate caused by the combination of ivabradine and ZD7288 was not significantly different from the changes caused by either drug alone. Application of cyclopiazonic acid (CPA, to inhibit SERCA) also reduced beating rate by about 150 bpm. ZD7288 alone, ivabradine and the combination of ZD7288 and ivabradine all depressed the log(concentration)-effect curves for the effect of isoproterenol on rate by similar amounts. CPA alone caused a greater depression of isoproterenol log(concentration)-effect curves than was the case with the I(f) blockers. The combination of I(f) blockers and CPA caused a profound further depression of the effects of isoproterenol on spontaneous rate so that the log(concentration)-effect curve was almost flat. The effects I(f) blockers and CPA were also investigated in guinea-pig isolated SAN myocytes loaded with the Ca2+ probe, fluo-5F, and were broadly comparable to those observed in intact spontaneously beating atria. The observations are consistent with roles for both I(f) and SR Ca2+ in the control of spontaneous beating rate. The balance between the contributions of different mechanisms to the control of spontaneous rate varies with conditions, particularly in their influence on the increase in rate caused by isoproterenol. The presence and function of Ca2+-stimulated adenylyl cyclases is likely to be an important factor with the potential to link the contributions of these interacting processes.