Preparation of nasal temperature-sensitive in situ gel of Radix Bupleuri and evaluation of the febrile response mechanism.

Objective: This study developed a nasal temperature-sensitive in situ gel system for Radix Bupleuri.

Method: Using 20% Poloxamer 407 as the gel base and 6% PEG 4000 adjusting the gelation temperature.

Results: The system is liquid at 4 degrees C. It can change its phase to gel above 30 degrees C, which is close to the temperature in nasal cavity. The antipyretic effect produced by Radix Bupleuri in situ gel formulation was investigated in fevered rabbits. The results show that it can prolong the effective time to 24 hours compared with 4-6 hours in Radix Bupleuri intranasal solution. The antipyretic response mechanism was researched by evaluating the relationship between body temperature and concentrations of cyclic adenosine monophosphate in cerebrospinal fluid. The results showed that the two parameters were positively correlated (r = 0.9435, P < 0.05). Six hours later after given in situ gel, the concentrations of cAMP were significantly lower than those in the solution group. It confirmed that temperature-sensitive Radix Bupleuri in situ gel applied in the nasal sprays had a longer residence and release time.

Conclusion: Radix Bupleuri nasal temperature-sensitive in situ gel has a higher medical effect and a longer effective time. Compared to the traditional nasal spray, it is more applicable for the treatment of fever.