Digoxin bioequivalence study: determination in human plasma by microparticle enzyme immunoassay

Objective: In this study a bioanalytical method for digoxin quantification was developed using Abbott AxSYM (R) Digoxin 11 with fluorescence detection to assess the bioequivatence of two digoxin tablet formulations (Digox 0.25 mg tablet from Pharlab Ind. Ltd., Brazil as test formulation and Digoxin (R) 0.25 mg tablet from Laboratorio Glaxo SmithKline, Brazil as reference formulation). Material and methods: 30 healthy volunteers (both sexes) received a single oral dose of digoxin in an open, randomized, two-period crossover study with a seven half-life washout interval of at least (21 days). Plasma samples were obtained over a 288-h interval after each oral administration of digoxin. The present method utilizes microenzyme particle immunoassay technology, in which the digoxin in the sample binds to anti-digoxin-coated microparticles and after separation; digoxin-alkaline phosphatase conjugate binds to the available sites remaining, Digoxin concentrations are calculated from the fluorescent products generated as a result of substrate (4-methylumbelliferyl) passage through the matrix cell. Results: The method was shown to be specific and sensitive with good accuracy and precision. The geometric mean and 90% confidence intervals (CI) for the Digox/Diaoxin (R) ratio were 107.62% (96.71 - 119.80%) for AUCO(0-t), 97.15% (80.54 - 117.19%) for AUC(0-inf), and 91.23% (83.55 - 99.62%) for C-max. Conclusion: Since the 90% CI for the parameters were all within the 80 - 125% interval proposed by the US Food and Drug Administration Agency, the two formulations were considered bioequivalent in terms of rate and extent of absorption.45636637