Nebulised Rt-PA for ARDS Due to COVID-19

This is a phase II, open label, uncontrolled, repeated dose, pilot trial of nebulised rt-PA in patients with COVID-19 ARDS.

The study recruited patients requiring either invasive mechanical ventilation (IMV) or non-invasive ventilation/non-invasive respiratory support (NIV/NIRS) between April 2020 and February 2021. Eligible patients (or if patients lacked capacity, their legal representative) were provided with an information sheet and informed consent was sought. Eligibility was assessed via routine clinical assessments, which may have been done prior to consent. The only exceptions were pregnancy tests (blood or urine), and possibly any assessments that were not done as per routine care. If required, these would have been done following consent, and all screening assessments must have been done during the 24-hour period before dosing with rt-PA.

In the rt-PA treatment group of cohort 1, 9 consented patients received nebulised rt-PA in addition to standard of care (SOC). Out of the 9 patients, 6 were on the IMV arm and another 3 were on the NIV arm. As an observational arm, matched historical controls who received only SOC were also recruited at a ratio of 2 controls to every 1 treatment arm patient, to ensure that any changes were not entirely due to disease resolution. A total of 18 patients were recruited to the historical matched control arm of cohort 1. Therefore a total of 27 patient constituted cohort 1.

For patients in the treatment group, 10 mg of rt-PA dissolved in 5 ml of diluent was given every 6 hrs for 3 days. This was extended to up to 14 days with a subsequent protocol amendment. Dose modifications were not permitted. Efficacy was described as the change in PaO2/FiO2 ratio from baseline, daily during treatment, end of treatment, 3 days post end of treatment and 5 days post end of treatment.

With a second surge of COVID-19 in early 2021, cohort 2 was opened to recruit more patients to provide additional data on the safety of rt-PA. Fewer timepoints were collected, which allowed for more rapid recruitment while at the same time not compromising safety monitoring. A more flexible dosing regimen for rt-PA was utilised. Patients on IMV received 60mg daily over three doses for up to 14 days. NIV patients received 60mg daily over 3 doses for two days, followed by 40mg daily over two doses for up to 12 days. A total of 26 patients were recruited in cohort 2, 12 on the IMV arm and 14 on the NIV/NIRS arm.

From the end of the treatment phase (after Day 14), patients were followed up in accordance with SOC for 28 days from the day of first dose of rtPA.

Safety monitoring was performed by assessment of the incidence and severity of bleeding events, and by the monitoring of plasma fibrinogen levels and routine coagulation parameters. Additional samples were taken for exploratory assessment of potential biomarkers, including, but not restricted to, PAI- 1, alpha 2 antiplasmin and a range of inflammatory cytokines and coagulation proteins. All other monitoring was done as per SOC.

A Data Monitoring Committee (DMC) was set-up to review safety data within the trial along with the final study results and advise on progressing from a pilot study to a randomised control trial based on the safety and efficacy data that was to be collected. If a patient had major pulmonary bleeding at any time, further dosing of patients was to be stopped and an ad-hoc DMC review to be arranged before resuming dosing (see section 12.2 Data Monitoring Committee).

Although there is extensive experience with the use of nebulised rt-PA in the context of the underlying inflammation, safety measures were included in the study. A gap of 24hrs was maintained between the first and second patient. At 24hrs, if patient 1 had no evidence of major pulmonary bleeding suggesting exaggerated alveolar fibrinolysis and no evidence of fibrinogen reduction of more than 50% (suggestive of systemic absorption), then the second patient was to be dosed. Both patients were evaluated for 72 hrs post dose for any major pulmonary bleeding and if no bleeding was noticed, then the rest of the cohort were to be recruited after the review of the safety data by the trial management group comprised of the investigators. Any concerns with the data were referred to the DMC for review. If the safety profile was acceptable, dosing of the third and subsequent patients in the rt-PA group would resume with no required interval between patients.

A statistically powered randomised controlled trial (RCT) would be ideal to define the magnitude of benefit and impact on overall survival and is the typical design in patients with ARDS. Although there is clinical data on the safety of nebulised rt-PA, there is no data in this clinical condition to facilitate a sample size calculation. There is data from a small RCT that has used another fibrinolytic agent, but the doses were not comparable. When a patient is randomised to receive no treatment, this precludes participation in other interventional studies which might decrease the risk of mortality. The most recent figures suggest a 50% mortality in patients receiving IMV. Currently there is a concerted effort to introduce multiple therapies based on our understanding of the pathophysiologic basis of the disorder. Further, if this pilot study shows significant effect in a subset of patients, there would be justification to progress to a statistically powered RCT. In the event of major adverse drug reactions or minor improvement in the oxygenation as assessed by PaO2/FiO2 , there are minimal gains to be had with a larger randomised control study.