Nanoemulsion Components Screening and Selection: a Technical Note

Nanoemulsions are isotropic, thermodynamically stable transparent (or translucent) systems of oil, water, and surfactants with a droplet size usually in the range of 10–100 nm (1,2). Their long-term stability, ease of preparation (spontaneous emulsification), and high solubilization of drug molecules make them promising as a drug delivery tool. They have found wide applications in oral drug delivery to enhance the solubility and bioavailability of the lipophilic drugs (3–5). Recently, there has been a surge in the exploration of nanoemulsions for transdermal delivery (6–8). They are also being investigated ardently for potential applications in ocular (9,10), pulmonary (11), nasal (12,13), vaginal (14,15), and parenteral drug delivery (16–18). The use of nanoemulsions in drug delivery has been reviewed, and it was noted that most studies have not been very systematic with regard to selection of surfactants and cosurfactants. The main objective of this study was to provide an efficient screening approach for the proper selection of oils, surfactants, and cosurfactants for the nanoemulsion formulation development. Ropinirole was selected as a model lipophilic drug for this purpose (Log P = 3.32). These systems often require high surfactant concentration, and this may lead to toxicity and irritancy problems. Therefore, judicious selection of surfactants along with their optimum concentration is required, which has been discussed in this report. Determination of the influence of the surfactant-to-cosurfactant mass ratio (Smix) on the nanoemulsion formation region also formed an important aspect of the study. Optimum selection would aid in better formulation with desirable attributes.