Intranasal trimethyl chitosan-coated emulsomes containing tizanidine as brain-targeted therapy in spasticity: formulation, optimization, and pharmacokinetic assessment

Tizanidine HCl (TZN) is an FDA-approved medication for treating spasticity. However, its oral administration presents obstacles to its efficacy, as it has a short duration of action and a low rate of absorption into the circulation (less than 40%) due to its rapid breakdown in the liver. In addition, its hydrophilic properties limit its capacity to cross the blood–brain barrier, thereby prohibiting it from reaching the central nervous system, where it can exert its intended therapeutic effects. Furthermore, diet-dependent absorption leads to fluctuations in bioavailability. Thus, this work aimed to create TZN-loaded chitosan-coated emulsomes (TZN-CTS-EMS) for intranasal administration, bypassing hepatic metabolism and boosting brain bioavailability. TZN-CTS-EMS were made using a thin film hydration approach. The influence of the independent parameters on the vesicle characteristics was examined and optimized using a Box-Behnken experimental methodology. The optimized formulation expected by the experimental design exhibited a greater desirability factor, characterized by a smaller particle size (127.63 nm), higher encapsulation efficiency (67.36%), and higher zeta potential (32.49 mV). As a result, it was chosen for additional in vivo assessment. Histopathological examinations showed no structural injury or toxicity to the nasal mucosa. Compared to intranasal TZN solution (TZN-SOL), the pharmacokinetics analysis demonstrated that intranasal TZN-CTS-EMS had a relative bioavailability of 191.9% in the plasma and 459.3% in the brain. According to these findings, intranasal administration of the optimized TZN-CTS-EMS may represent a viable, noninvasive substitute for effective TZN delivery to brain tissues, potentially leading to improved safety and pharmacological efficiency.