Quantitative analysis of drug delivery to the brain via nasal route

The blood–brain barrier (BBB) prevents drugs' permeability into the brain and limits the management of brain diseases. Intranasal delivery is a convenient route of drug administration that can bypass the BBB and lead to a direct delivery of the drug to the brain. Indeed, drug accumulation in the brain following intranasal application of a drug solution, or of a drug encapsulated in specialized delivery systems (DDSs), has been reported in numerous scientific publications. We aimed to analyze the available quantitative data on drug delivery to the brain via the nasal route and to reveal the efficiency of brain drug delivery and targeting by different types of nasally-administered DDSs. We searched for scientific publications published in 1970–2014 that reported delivery of drugs or model compounds to the brain via intranasal and parenteral routes, and contained quantitative data that were sufficient for calculation of brain targeting efficiency. We identified 73 publications (that reported data on 82 compounds) that matched the search criteria and analyzed their experimental settings, formulation types, analytical methods, and the claimed efficiencies of drug brain targeting: drug targeting efficiency (%DTE) and nose-to-brain direct transport (%DTP). Outcomes of this analysis indicate that efficiency of brain delivery by the nasal route differs widely between the studies, and does not correlate with the drug's physicochemical properties. Particle- and gel-based DDSs offer limited advantage for brain drug delivery in comparison to the intranasal administration of drug solution. Nevertheless, incorporation of specialized reagents (e.g., absorption enhancers, mucoadhesive compounds, targeting residues) can increase the efficiency of drug delivery to the brain via the nasal route. More elaborate and detailed methodological and analytical characterizations and standardized reporting of the experimental outcomes are required for reliable quantification of drug targeting to the brain by the nasal route. Quantitative analysis of these data will facilitate the development of DDSs with high brain targeting efficiency.