# Has the Toxicity of Therapeutic Deep Eutectic Systems
## 3 Animal Models
### Injection Routes: Transdermal/Subcutaneous/Intravenous Administration  
Injection administrations require the drug to be delivered through the skin with a needle (subcutaneous, intravenous, or transdermal). Some drugs are delivered body-wide through a patch on the skin. These drugs are sometimes mixed with chemical compounds, as DESs, that enhances penetration through the skin into the bloodstream without any injection. According to transdermal skin delivery, it is difficult to assess the skin permeability of materials using only in vivo experiments. Consequently, numerous ex vivo models are frequently employed to assess drug skin permeation profiles and kinetic parameters [96]. [PERSON] et al. used DESs to formulate a nanocomplex for the systemic administration of verterporfin, a chemotherapeutic drug. They investigated the efficacy of the nanocomplex \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Route of Administration** & **Components** & **Animal Model** & **Reference** \\ \hline Injection: transdermal & & & \\ (in vivo) + porcine skin (ex vivo) & & CAGE + insulin & Male Wistar rats and Porcine skin & [83] \\ \hline Injection: transdermal skin & & & \\ (ex vivo) & & CAGE + insulin & Porcine skin & [84] \\ \hline Injection: subcutaneous & & & \\ (in vivo) & & & \\  & & & \\  & & & \\  & & & \\  & & & \\  & & & \\ \hline Injection: transdermal & & & \\  & & & \\  & & & \\  & & & \\  & & & \\  & & & \\ \hline Injection: transcranial & & & \\  & & & \\  & & & \\  & & & \\  & & & \\  & & & \\  & & & \\ \hline Injection: signal & & & \\  & & & \\  & & & \\  & & & \\  & & & \\  & & & \\  & & & \\ \hline \end{tabular}
\end{table} 
Table 3: _Cont._administered intravenously in female mice bearing a 4T1 tumor in the mammary pad. The authors observed a better drug penetration into the tumor tissue, probably due to the DESs' contribution to the fluidization of the tissue through the interaction between the DESs and membrane lipids. In addition, greater drug sensitivity and effective inhibition of orthotopic tumor growth was shown [81]. The same authors reported a deep eutectic-based formulation that slows the release of apomorphine after subcutaneous injection. In this case, CAGE1:2 and a mixture with the drug was prepared, which is called SEAPORT formulation. The skin from the dorsal side of Wistar rats was used to study apomorphine release from SEAPORT ex vivo and it was observed that CAGE 1:2 plays a critical role in its release. Moreover, in vivo pharmacokinetic of the apomorphine from subcutaneously injected SEAPORT was measured in the rats and pigs and showed a prolonged duration of a higher apomorphine concentration in plasma in comparison to the clinical comparator (reference drug formulation) [82]. Other studies also synthesized CAGE, as DESs, and included them in drug formulations for the application in ex vivo and in vivo models, mainly with insulin, because of its difficult transdermal delivery by conventional chemical permeation enhancers. [PERSON] et al. reported that CAGE can deliver insulin across porcine skin and significantly reduce blood glucose levels in rats when insulin-CAGE is topically administered. The ex vivo penetration into the skin samples was measured using porcine skin; to measure the insulin-CAGE penetration, Fluorescein isothiamate-labeled insulin (FITIC-insulin) was added to CAGE and applied to the porcine skin. In vivo experiments were performed in male rats applying transdermal insulin in CAGE [83]. [PERSON] et al. synthesized variants of CAGE by controlling the ratio of a range of 1:4 to 2:1. In this case, an ex vivo pig's skin model demonstrated that the 1:2 and 1:4 molar ratio variants were capable of transporting FITIC-insulin through to the stratum corneum, epidermis, and dermis (transdermal transport) [84]. Recently, [PERSON] et al. developed a new tool toward improving subcutaneous formulation using biocompatible deep eutectics.