A modulated release, multiunit oral drug delivery technology using a system based on ionic interactions of anions of salts with quaternary ammonium ions of the ammoniomethacrylate polymer is described. The system consisted of a drug layered, EUDRAGIT NE-coated salt core which was further coated with EUDRAGIT RS. The relative effects of different anions on the polymer permeability have been investigated by studying their influence on the in vitro drug release. A prototype formulation of metoprolol succinate using this technology was developed and the drug release from the formulation was adjusted to have a release profile which would match the circadian rhythm i.e. a higher amount of drug would be available after an initial lower release (accelerated type of release). The formulation was tested in vivo in 12 healthy human volunteers in an open label, randomized, two-treatment, two-period, single dose crossover bio-study with reference formulation Beloc-zok. The in vivo release demonstrated that compared to the reference, a higher amount of drug was available in the plasma from the 7th hour onwards. A higher AUC of the drug was also observed compared to the reference formulation. An in vitro-in vivo correlation was attempted to identify a bio-relevant in vitro dissolution medium for the formulation.