Development of Sustained Release Chitosan/β-Glycerol Phosphate-Based Injectable Thermo-Gels Containing Naproxen Sodium: In-Vitro and In-Vivo Evaluation

To develop in-situ chitosan/β-glycerol phosphate (β-GP) thermogels loaded with naproxen sodium for sustained drug delivery, to circumvent issues related with prolonged oral administration of naproxen (e.g. ulceration, abdominal discomfort, diarrhoea, bloating, etc.). To overcome these complications, in-situ gel formulations are developed as a promising strategy for long-term management of chronic inflammatory disorders such as arthritis. Furthermore, this system is evaluated with an earlier naproxen formulation prepared using sodium alginate.

Thermogels containing varying chitosan concentrations were prepared at pH 7.4 and 37°C, followed by drug loading. Key physicochemical properties, including injectability, gelation time, and sol-gel fraction, were evaluated. In-vitro release studies were conducted using a dialysis membrane with a USP dissolution basket apparatus-I. Anti-inflammatory efficacy was assessed in Sprague-Dawley rats with carrageenan-induced hind ankle inflammation.

Results indicated that formulations with higher polymer content exhibited shorter gelation times and increased gel fractions. In-vitro release from F6CGP demonstrated sustained naproxen sodium delivery, following the Korsmeyer-Peppas model with Fickian diffusion kinetics (n ≤ 0.45). In-vivo, the swelling of the inflamed hind ankle joint decreased progressively over 72 h (≈ -2.6 ± 0.73 mm), confirming effective anti-inflammatory action; relatively better as compared to the previous sodium alginate system.

In-situ chitosan/β-glycerol gel-forming injectable formulation F6CGP provides sustained naproxen sodium release and shows potential as a therapeutic strategy for chronic inflammatory conditions such as arthritis. The results also indicate that this polymeric system can play a key role in modulating critical formulation parameters i.e. gelation time, gel fraction, injectability, drug release etc.