Smart P407-based Thermogels Containing 5-ASA as Next Generation Rectal Formulations for the treatment of Inflammatory Bowel Diseases

Introduction: Inflammatory bowel disease (IBD) is a chronic inflammatory disorder of the gastrointestinal tract that severely compromises quality of life. First-line therapy with 5-aminosalicylic acid (5-ASA) is limited by poor solubility, rapid absorption in the upper gut, and insufficient colonic delivery. Rectal formulations may overcome these issues, but conventional suppositories and enemas often reduce patient compliance.

Methods: Poloxamer 407 (P407)-based thermosensitive hydrogels were prepared using the cold method by dissolving the copolymer (20% w/w) in cold water and incorporating 5-ASA (0.1-0.5% w/w). The systems were characterized by rheological behavior, gelation temperature, mucoadhesive strength, injectability and spreadability. Drug release was evaluated at pH 5.0 and 7.4 by dialysis and membrane-less methods. Anti-inflammatory effects were tested in lipopolysaccharide -activated RAW264.7/Caco-2 co-cultures and in dextran sodium sulfate (DSS)-induced murine colitis model.

Results: The optimized P407-5-ASA hydrogel showed rapid gelation at physiological temperature, mucoadhesion, shear-thinning flow and easy syringeability, ensuring patient-friendly administration. 5-ASA showed prolonged release profiles even under acidic conditions. In vitro tests demonstrated that the formulation decreased both the macrophage infiltration and TNF-α secretion compared to free drug. Rhodamine-labelled gels demonstrated prolonged colon retention and P407-5-ASA markedly improved the therapeutic outcomes in DSS-treated mice with respect to commercial 5-ASA.

Conclusions: P407-based in situ hydrogels provide a high-performance, patient-acceptable platform for localized IBD therapy. They enhance 5-ASA efficacy and retention combining thermo-responsive gelation, mucoadhesion and sustained release while minimizing systemic exposure.

The obtained results support their potential as next-generation rectal formulations to improve the therapeutic outcomes and adherence in IBD patients.