Cyclodextrins in topical gel formulation as photoprotective system for Nabumetone

Photostability studies applied on aqueous solutions of Nabumetone, an anti-inflammatory drug used in the treatment of osteoarthritis and rheumatoid arthritis, have confirmed the sensitivity to light of this compound, revealing the 6-methoxy-naphthalene-aldehyde as the main photoproduct. In this work, the stability of NA-cyclodextrin (CD) complexes was investigated in gel formulation potentially suitable as sustained-release systems. The photodegradation experiments were realized under stressed conditions according to the ICH rules and monitored by spectrophotometry. The spectral data were processed by Multivariate Curve Resolution (MCR), able to estimate spectra and concentration profiles of the components involved in the kinetic process. NA entrapped in cyclodextrin and formulated in solution and gel preparations were exposed to an irradiance power of 350 W/m2. Encapsulation percentage of the drug in several cyclodextrins was measured, recording an increase of the water solubility in the order hpβCD>mβCD>βCD. No significant photoprotection of NA was measured in aqueous solution. On the contrary, the gel containing the hpPCD-complex showed relevant stability. The photoprotective ability of this formulation was further increased by adding ascorbic acid 2%, still detecting 90% of the starting concentration after 90 min of light exposure.