**4. Discussion**

Data in the literature show that each of the non-steroidal anti-inflammatory drugloaded nano-formulations was demonstrated to be beneficial in correct pain management, leading to a safer and more precise medication. Furthermore, the prolonged release of the antinociceptive agents from nano-systems delivers an effective concentration of active drug for a long period of time [44–48].

The delayed onset of the analgesic activity, and the prolongation of the antinociceptive action of the nano-DEX, can be attributed to the particularities in the release of the drug entrapped into liposomes stabilized with chitosan.

Given its biological half-life and physico-chemical characteristics, dexketoprofen is a good drug candidate for prolonged release, in order to improve patient compliance by reducing dose frequency. It has been formulated in prolonged released mini-matrix tablets [49], minitablets coated with Eudragit S and ethylcellulose for colon targeting [50], and gastroretentive systems by the wet granulation method with various grades of hydroxylpropyl methyl cellulose (HPMC) [51]. All these dosage forms have proved a modified release profile.

Various methods have been implemented for preparing more evolved carriers, such as nanosystems containing dexketoprofen, all demonstrating to provide prolonged release of the drug and to maintain the analgesic effect for several hours [52–55].

We obtained original formulations of DEX loaded nanoparticle systems with chitosan and phosphatidylcholine. These new systems were physico-chemically and structurally characterized, tested for biocompatibility, and the in vitro release of drugs was studied. Additionally, we tested how DEX-loaded nanoparticles influenced nociceptive sensitivity compared to the free drug on a standard experimental somatic pain model in rats.

The advantages of these nanoparticulate systems rely on the extended release of DEX, which provides a prolongation of antinociceptive effects in the hot plate test in rats.

Ozturk et al. prepared DEX-loaded nanoparticles by spray-drying with Eudragit 100 RL, which displayed controlled release kinetics, with prospects of prolonging DEX analgesic activity [26]. Using other encapsulating agents, such as Compritol ATO 888 and Dynasan 114, the same research team prepared solid lipid nanoparticles containing DEX, which demonstrated prolonged analgesic activity for up to nine hours in the writhing test in mice [56].

DEX was also used as a model drug form obtaining modern, new systems nanocochleates—in combination with other drugs [52]. We prepared nanosystems as unilamellar liposomes entrapping dexketoprofen, using chitosan, with good stability and uniform size range. In our experimental conditions, the use of lipid vesicles entrapping DEX did not induce substantial blood element discrepancies, biochemical changes, and immune parameters modifications; all these findings support the idea that these new systems have a good in vivo biocompatibility in rats.

The in vivo release of DEX from nanoparticles was not tested, which represents one limitation of the study; another limitation consists of the small number of animals used in the experiment.
