Study to Evaluate the Efficacy and Safety of Plitidepsin in Adults with Post-COVID-19 Condition (PCC)

The study aims to prove that plitidepsin could be an efficacious, safe, and well-tolerated therapy for PCC. To this end, we will perform a randomized, double-blind study comparing the clinical and laboratory benefits of plitidepsin vs. placebo in 90 subjects with moderate to severe functional disability. The study consists of an intervention period and a follow-up period, with a total of 135 +/-3 days approximately between both periods. During the intervention period, four treatment cycles will be administered, scheduled every 15 days (every 2 weeks), with intravenous (IV) infusion over three consecutive days. After completing the intervention period, a 90-day (+/-5) follow-up period will be conducted. Subjects in arm A will receive the plitidepsin 1.5 mg/day 1h-IV during the four treatment periods on Days 1 to 3, Days 15 to 17, Days 29 to 31 and Days 43 to 45. Subjects in arm B will receive 1h-IV placebo 1 vial /day during the first two treatment periods and will receive the plitidepsin 1.5 mg/day 1h-IV during the last two treatment periods. Subjects in arm C will receive 1h-IV placebo 1 vial/day during the four treatment periods.

Plitidepsin, a marine-derived cyclic depsipeptide that inhibits SARS-CoV-2 replication at nanomolar concentrations by targeting the host protein eukaryotic translation elongation factor 1A, could be a suitable candidate treatment for "Long COVID" because of a triple mechanism of action; a) it has demonstrated potent anti-SARS-CoV-2 in vitro activity, (b) it has a systemic anti-inflammatory effect, detailed in the text below, and (c) has an anti-herpes antiviral effect, which could provide additional therapeutic benefits to prevent herpesvirus reactivation seen in Long-COVID. An interim analysis will be conducted upon reaching 30% and 50% of recruitment (patients treated with at least one dose and 28 days (+/- 2 days) of FUP)). The first interim analysis will focus exclusively on safety assessment, based on adverse events reported to date. The second interim analysis (50%) will evaluate safety and futility. A blinded safety report will be prepared, summarizing adverse events, and submitted to the Data Safety Monitoring Board (DSMB) for review and to determine whether to continue, modify, or terminate the study