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.