Jin‐Ho Choy

The coronavirus disease 2019 (COVID‐19) pandemic is a serious global threat with surging new variants of concern. Although global vaccinations have slowed the pandemic, their longevity is still unknown. Therefore, new orally administrable antiviral agents are highly demanded. Among various repurposed drugs, niclosamide (NIC) is the most potential one for various viral diseases such as COVID‐19, SARS (severe acute respiratory syndrome), MERS (middle east respiratory syndrome), influenza, RSV (respiratory syncytial virus), etc. Since NIC cannot be effectively absorbed, a required plasma concentration for antiviral potency is hard to maintain, thereby restricting its entry into the infected cells. Such a 60‐year‐old bioavailability challenging issue has been overcome by engineering with MgO and hydroxypropyl methylcellulose (HPMC), forming hydrophilic NIC–MgO–HPMC, with improved intestinal permeability without altering NIC metabolism as confirmed by parallel artificial membrane permeability assay. The inhibitory effect on SARS‐CoV‐2 replication is confirmed in the Syrian hamster model to reduce lung injury. Clinical studies reveal that the bioavailability of NIC hybrid drug can go 4 times higher than the intact NIC. The phase II clinical trial shows a dose‐dependent bioavailability of NIC from hybrid drug suggesting its potential applicability as a game changer in achieving the much‐anticipated endemic phase.