Photostability studies on nicardipine–cyclodextrin complexes by capillary electrophoresis

Nicardipine (NC)–cyclodextrin solid systems were prepared in equimolar ratios and their photostability in aqueous solution under exposure to UV(A)–UV(B) radiations was evaluated. The photodegradation process was monitored by a capillary electrophoresis (CE) method able to provide the enantioresolution of the rac-nicardipine. Enantioresolution was achieved using the mixture 3.0% sulfate-β-cyclodextrin (SβCD) and 2.0% heptakis(2,3,6-tri- O-methyl)-β-cyclodextrin (TMβCD) as chiral selector in 20 mM triethanolammonium phosphate solution (pH 3.0). The photostability studies were carried out on inclusion complexes of rac-nicardipine with α-cyclodextrin (αCD), β-cyclodextrin (βCD), γ-cyclodextrin (γCD), hydroxypropyl-α-cyclodextrin (HPαCD), hydroxypropyl-β-cyclodextrin (HPβCD), hydroxypropyl-γ-cyclodextrin (HPγCD), (2-hydroxyethyl)-β-cyclodextrin (HEβCD) and methyl-β-cyclodextrin (MβCD). A photoprotective effect was observed by βCD, HPαCD, HEβCD, whereas γCD, MβCD, HPβCD and HPγCD did not affect the nicardipine photostability. Conversely, αCD was found to favour the drug photodegradation. Evidences for CD s-mediated stereoselective photodegradation of rac-nicardipine were observed only for the β-CD complex. In this case, two distinct photodegradation profiles, with two different kinetic constants ( k), were observed for the nicardipine enantiomers.