Evaluation of photochemical degradation of digoxin by Na,K-ATPase assay

A simple Na,K-ATPase assay is described as a suitable method for testing of digoxin photodegradation. The exposure of Na,K-ATPase to the photodegraded samples exhibited reduced inhibition of the enzyme, compared to the unirradiated samples containing equal initial concentrations of drug. The degree of inhibition was dependent on the irradiation time. The concentrations of digoxin in irradiated samples were evaluated by HPLC analysis. Excellent agreement of the results obtained by both methods was observed. The investigation of the influence of irradiated samples on Na,K-ATPase inhibition revealed no side products acting as Na,K-ATPase inhibitors. The cytokinesis block micronucleus test (CBMN) was applied in order to investigate the cytotoxicity of the possible degradation products after exposure to UV irradiation. The results confirmed that the photochemical treatment did not induce the cytotoxic side products. Zero order kinetics, which was observed for digoxin photodegradation and the associated reaction mechanism are also discussed.