Inclusion complexes of nifedipine and other 1.4-dihydropyridine derivatives with cyclodextrins. IV. The UV study on photochemical stability of the inclusion complexes of nisoldipine, nimodipine, nitrendipine and nicardipine with beta-cyclodextrin in the solution.

The results of measurements of photochemical stability of the inclusion complexes formed by nimodipine (NM), nisoldipine (NS), nitrendipine (NR) and nicardipine (NC) with beta-cyclodextrin (beta-CD) are reported. The inclusion complexes were obtained in solution. The formation of inclusion complexes in the liquid phase was estimated from a phase solubility diagram. The analysis of solubility curves in the phase diagram permitted calculation of stability constants of the inclusion complexes formed. Photochemical stability of 1.4-dihydropyridine derivatives obeyed the 1 order kinetic equation. The photodegradation of NM, NR and NC was found to be a single stage reaction. The photodegradation of NS occurred in two stages. In the inclusion complexes the photosensitivity of all studied DHP derivatives decreases. The complexation with beta-CD improved their photostability by 5-10 times. The greatest decrease in the photodegradation rate was observed for the most photosensitive compound NS whose photostability increased 100 times when in inclusion complex with beta-CD.