Cucurbit[7]uril-based host-guest complexes for improving bioavailability and reducing side effects of piroxicam

Piroxicam (PX) is a nonsteroidal anti-inflammatory drug (NSAID) commonly associated with gastrointestinal (GI) injuries, including dyspepsia, heartburn, inflammation, bleeding, ulceration, and life-threatening perforation. The β-cyclodextrin (β-CD)-based PX formulation (PX@CD) has been shown to reduce gastric side effects by improving PX's solubility and dissolution rates. However, the solubility of PX can only be increased to a limited extent by β-CD, due to the low binding constant between PX and β-CD (∼100 M^-1). As a result, adverse reactions such as epigastric pain and pyrosis are still commonly reported. Cucurbit[7]uril (CB[7]) is a synthetic macrocyclic host compound that binds strongly to various drugs. In this study, we demonstrated that CB[7] forms complexes with PX in the gastric acid environment with a binding constant approximately 70 times higher than that between β-CD and PX. The PX@CB[7] inclusion complexes exhibited rapid dissolution rates in the gastric environment. In addition, PX@CB[7] showed significantly higher oral bioavailability and maximum concentration (C_max) compared to PX and PX@CD (1:2.5), resulting in improved anti-inflammatory effects in both mouse and rat models. Moreover, PX@CB[7] (1:2.5) had the least adhesion to the gastric mucosa and caused the mildest gastric side effects in rat models when compared to PX, PX@CD (1:2.5), and PX@CB[7] (1:1). Lastly, CB[7] demonstrated good oral biocompatibility in a subacute toxicity evaluation study. These findings indicate that CB[7] could be used as an excipient to improve treatment effectiveness and decrease adverse reactions in orally administered formulations with a favorable safety profile.