Self-nanoemulsifying Drug Delivery Systems: Formulation Insights, Applications and Advances

Abhijit A Date; Neha Desai; Rahul Dixit; Mangal Nagarsenker

Disclosures

Nanomedicine. 2010;5(10) 

In This Article

Nanoemulsions & SNEDDS: Controversy Regarding the Role of Nano-size in Augmenting the Drug Transport Across Biological Membranes

There are numerous examples in the literature that establish potential of the nanoemulsions and SNEDDS in augmenting efficacy of various therapeutic agents. However, enhanced therapeutic efficacy obtained with the nanoemulsions is a combined result of a multitude of factors. In general, it is believed that nanoscale offers better transport properties and is a major driving factor for the augmented therapeutic efficacy of drugs. However, the role of nanoscale in improving the transport of drug across biological membranes and therapeutic efficacy is debatable in the case of nanoemulsions. Almost two decades ago, Tarr and Yalkowsky established that the size of emulsion has a significant effect on the absorption of the cyclosporine through rat intestine, suggesting the rationale behind development of nanoscale emulsions.[99] In another investigation, de Smidt et al. demonstrated that penclomedine nanoemulsions (droplet size ~160 nm) have greater bioavailability compared with that of penclomedine emulsions (droplet size ~750 nm).[100] However, few recent reports suggest that the nano-size of the nanoemulsion may not have significant influence on the drug permeation/absorption and pharmacokinetics of the drug. Yap and Yuen evaluated pharmacokinetics of tocotrienol emulsion and nanoemulsion (with significant difference in the droplet size and digestibility) in humans.[101] Interestingly, tocotrienol emulsion and nanoemulsion did not show any difference in pharmacokinetic parameters. In another study, Nielsen et al. compared the pharmacokinetics of probucol self-emulsifying formulation (droplet size ~4.5 µm) and self-nanoemulsifying formulation (droplet size ~45 nm) in minipigs and no significant difference was observed in the pharmacokinetics of self-emulsifying and self-nanoemulsifying formulations.[87]

In an intriguing study, Izquierdo et al. systematically compared the ability of emulsions and nanoemulsions to improve the skin permeation of tetracaine, a topical anesthetic agent.[102] The emulsions and nanoemulsions employed in the study had significantly different droplet sizes but had the same composition of the surfactant and oil phase. Interestingly, the authors observed no significant difference in the tetracaine dermal and transdermal permeation for emulsions and nanoemulsions. This report clearly indicates a need for reassessing the role of the specific nano-size of the nanoemulsions in dermal/transdermal delivery and warrants generation of more data in this area. Thus, the role of nano-size of the nanoemulsions in improving drug transport across biological membranes and pharmacokinetics needs to be evaluated extensively and critically.

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