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A Multiphasic Absorption Model Best Characterizes Gastrointestinal Absorption of Divalproex Sodium Extended‐Release Tablets

D sodium extended-release (divalproex-ER) tablet is a novel once-daily formulation that offers the potential advantages of improved medication adherence, increased patient convenience, and easier titration to maximum effective dose while possibly reducing the risk of side effects (by reducing peaktrough fluctuations in plasma concentrations). Divalproex-ER is based on hydrophilic matrix technology; drug release is controlled primarily by erosion of a water-soluble polymer (hydroxypropylmethyl cellulose) from the matrix. We have previously quantified the mean input absorption rate parameter value for valproic acid (VPA) from orally administered divalproex-ER as 0.0431 mg/h/mg dose, representing a pseudo zero-order absorption rate from this formulation. Closer inspection of this VPA absorption profile from divalproex-ER revealed that our characterization could be optimized. In particular, we needed to distinguish this formulation’s true absorption characteristics that cannot be characterized by simple absorption models (eg, firstand zero-order) and several atypical absorption models (mixed zeroand first-order, Weibull function, timeand/or gastrointestinal [GI]-location-dependent, exponential, and several other absorption models) that have been proposed for other drugs or formulations. The purpose of this investigation was to expand our initial observations and more fully characterize, using a unique model, the absorption characteristics and single-dose pharmacokinetics of divalproex-ER tablets.