Development and evaluation of long-acting epidural smart thermoreversible injection loaded with spray-dried polymeric nanospheres using experimental design

Context: Reduction of injection frequency as well as localization of drug absorption in the injection site are important requirements in epidural pain treatment. Purpose: Our objective is to explore the production feasibility of controlled release thermoresponsive spray-dried tramadol HCl (TmH) nanospheres for localized epidural injection. Methods: A 2(4) factorial design was employed to study the effect of some selected variables. Results: F15 having the most extended release (MDT = 89.03 +/- 0.76 min) was selected, based on regression analysis, for further investigation and characterization. The selected nanospheres (particle diameter = 832.5 +/- 10.61 nm) with good flowing properties (theta = 28.076 +/- 1.20) was reconstituted with different concentrations of Poloxamer 407 (P407) solution. The optimum reconstituted F15 nanospheres, prepared using 20% w/w P407, was liquid at room temperature, exhibited sol-gel transition at 37 degrees C, was easily withdrawn and injected using 23G needle. The evaluation of the analgesic effect of the selected formula using hot plate method showed a desired rapid onset, yet, extended analgesic effect up to 24 h. The AUC(0 24 h) (2998.072 +/- 61.830) as well as E-max (200.788 +/- 12.123) were significantly higher than drug solution and control while T-max (2.200 +/- 1.095) was non-significant compared to both. Conclusion: the designed formula offers a promising approach as safe depot epidural analgesic.