Co-amorphous systems of sinomenine with nonsteroidal anti-inflammatory drugs: A strategy for solubility improvement, sustained release, and drug combination therapy against rheumatoid arthritis.

Rheumatoid arthritis (RA) is a chronic autoimmune joint disorder that affects about 1% of the world population and may lead to severe disability and comorbidity. Despite breakthroughs in past decades to understand its pathogenesis and the development of transforming disease-modifying antirheumatic drugs, the symptoms of many patients are not substantially improved. Sinomenine (SIN), a natural alkaloid with poor solubility, has been used to treat RA in China for years because of its unique immunoregulative activity. However, its commercial hydrochloride form has a short half-time, which may cause huge fluctuations of blood drug concentration leading to severe adverse reactions. In this study, co-amorphous systems of SIN with three nonsteroidal anti-inflammatory drugs (NSAIDs), including indomethacin, naproxen, and sulindac, were prepared for the combination therapy, as well as the improvement of its aqueous solubility and controlled release. Each co-amorphous sample was characterized by powder X-ray diffraction (PXRD), temperature-modulated differential scanning calorimetry (mDSC), and Fourier transform infrared spectroscopy (FTIR). The CO and NH stretching vibration in the three co-amorphous samples appears in FTIR spectra, suggesting the formation of salts between SIN and NSAIDs. SIN also exhibits sustained release rates in all three co-amorphous samples. These co-amorphous systems show excellent physicochemical stability because no recrystallization was observed at 25 °C and 75% relative humidity (RH) after four months. Our study suggests that SIN-NSAIDs co-amorphous systems represent an affordable and promising treatment against RA.