Intranasal drug delivery of antiviral agents - a revisit and way forward

Even to this date, oral drug delivery in the form of tablets, capsules, and syrups is considered as the most accepted one. However, oral delivery as a methodology requires that the active molecules and their formulations are water-soluble. Nasal drug delivery is characterized by ease of permeability through the epithelial mucosa, low enzyme activity, and a wide range of immunocompetent cells. For the transfer of drugs and active molecules through the nasal route, it is often essential to resort to nanodelivery methods, such as liposomes, microspheres, nanoemulsions, and so on. The use of nanodelivery vehicles has become more important in the modern context of viral infections, including those of the respiratory tract. Nanoformulations are developed in the form of nasal gels, sprays, drops, rinses, etc. Nanoformulations of antigens, vaccine and immune adjuvants, and antivirals are now gaining importance. There are promising reports on nanoparticles of metals, metal oxides, polymers, and so on that have the potential to detect and inhibit viruses by themselves. This review looks into the nasal nanoformulations in detail and provides an insight into how their efficacy can be improved. To overcome known drawbacks, such as degradation and active mucociliary clearance by antigenpresenting cells at the site of administration, polymers, such as PEG, are incorporated in the nanoformulation. Polymeric systems also provide better tunability of physicochemical properties. The mechanism of nasal spray-based drug delivery systems is also discussed in this paper. The review, thus, provides a detailed insight into the way forward for the development of nasal formulations.