Enabling oral delivery of antiviral drugs: Double emulsion carriers to improve the intestinal absorption of zanamivir

Antiviral drugs play a major role in the control of seasonal influenza epidemics and may provide prophylactic and therapeutic benefits during an eventual pandemic. Among the neuraminidase inhibitors, zanamivir has been shown to be a potent inhibitor of influenza viruses, and similarly against emerging resistant strains. Despite its high antiviral efficiency, zanamivir suffers from poor intestinal permeability, therefore administered via inhalation. Enabling oral delivery of zanamivir will augment the available antiviral tools in clinical practice, increase patient compliance and ultimately improve public health. Encapsulation of hydrophilic drugs within double emulsions (DEs), is an efficacious approach to enhance the oral bioavailability of BCS Class III drugs, such as zanamivir. The objective of this research was to increase the intestinal absorption of zanamivir by means of compatible DEs. Two different types of stable DEs were prepared comprising different internal aqueous phases (W₁). These micro-sized DEs showed high encapsulation efficacy (96.6–98.9 %) and markedly retarded the release rate of the antiviral drug. Both types of the zanamivir loaded DEs (zDEs) significantly increased the transport ability of zanamivir across a parallel artificial membrane. Furthermore, in-situ perfusion of zDEs revealed outstanding permeability of zanamivir across the intestinal wall of rats. The zDEs containing carbomer gel (rather than carboxymethyl cellulose) as W₁ obtained superior in-vivo effective permeability (P_eff); yet, both zDEs exhibited higher P_eff values (2–6-fold) than the low/high permeability marker (metoprolol). In conclusion, the DEs delivery system allowed overcoming the intestinal permeability barriers, towards successful oral administration of zanamivir.