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Essential oils are natural products with a complex composition. Terpenes are the most common class of chemical compounds present in essential oils. Terpenes and the essential oils containing them are widely used and investigated by their pharmacological properties and permeation-enhancing ability. However, many terpenes and essential oils are sensitive to environmental conditions, undergoing volatilization and chemical degradation. In order to overcome the chemical instability of some isolated terpenes and essential oils, the encapsulation of these compounds in nanostructured systems (polymeric, lipidic, or molecular complexes) has been employed. In addition, nanoencapsulation can be of interest for pharmaceutical applications due to its capacity to improve the bioavailability and allow the controlled release of drugs. Topical drug administration is a convenient and non-invasive administration route for both local and systemic drug delivery. The present review focuses on describing the current status of research concerning nanostructured delivery systems containing isolated terpenes and/or essential oils designed for topical administration and on discussing the use of terpenes and essential oils either for their biological activities or as permeation enhancers in pharmaceutic formulations.

This study reports the development of nanoemulsions intended for intravenous administration of thalidomide (THD). The formulations were prepared by spontaneous emulsification method and optimized with respect to thalidomide (0.01-0.05%, w/w), and hydrophilic emulsifier (polysorbate 80; 0.5-4.0%, w/w) content. The formulations were evaluated concerning physical appearance and drug crystallization; droplet size; zeta potential and drug assay. Only the formulation containing 0.01% THD and 0.5% polysorbate kept its properties in a satisfactory range over the evaluated period (60 days), i.e. droplet size around 200nm, drug content around 95% and zeta potential around -30mV. The transmission electron microscopy revealed emulsion droplets almost spherical in shape confirming the results obtained by photon correlation spectroscopy. Drug crystallization observed for higher content (THD 0.05%, w/w) nanoemulsions was investigated. The crystals observed at optical microscopy presented a different crystal habit compared to that of the raw material used. It was speculated whether the kind of THD polymorph employed could influence nanoemulsion formulation. Formulations were prepared with either one of THD polymorphs (β- or α-) and crystals were characterized by fourier transformed infrared spectroscopy (FTIR) and X-ray diffraction (XRD). It was observed that regardless of the polymorph employed (β- or α-), drug crystallization occurs in the α-form. THD solubility in oils was not influenced by the polymorphic form. In addition, the in vitro dissolution profile of the selected formulation (THD 0.01%, w/w; polysorbate 0.5%, w/w) was assessed by bulk-equilibrium reverse dialysis sac technique and demonstrated a release profile similar to that of a THD acetonitrile solution, with around 95% THD being dissolved within 4h. Finally, a pharmacokinetic simulation of an intravenous infusion of 250mL of the selected nanoemulsion suggests that the parenteral administration of a dose as low as 25mg might lead to therapeutic plasma concentrations of thalidomide.

In order to search for new approaches to treat glioma, intranasal administration has been proposed as an alternative route to deliver drugs into the brain. Among the drug alternatives, kaempferol (KPF) has been reported to induce glioma cell death. This study aimed to prepare nanoemulsions containing KPF with and without chitosan to investigate their potential for brain delivery following intranasal administration, and to evaluate their antitumor activity against glioma cells. KPF-loaded nanoemulsion (KPF-NE) and KPF-loaded mucoadhesive nanoemulsion (KPF-MNE) were prepared by high-pressure homogenization technique and were characterized for their globule size, zeta potential, drug content, pH, viscosity, mucoadhesive strength and morphology. KPF from KPF-MNE showed significantly higher permeation across the mucosa in ex vivo diffusion studies. Histopathological examination suggests both nanoemulsions to be safe for the nasal mucosa and able to preserve KPF antioxidant capability. KPF-MNE enhanced significantly the amount of drug into rat's brain following intranasal administration (5- and 4.5-fold higher than free drug and KPF-NE, respectively). In addition, KPF-MNE reduced C6 glioma cell viability through induction of apoptosis to a greater extent than either free KPF or KPF-NE. The mucoadhesive nanoemulsion developed for intranasal administration may be a promising system for delivery to the brain, and KPF-MNE is a candidate for further antiglioma trials.

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