Once-a-day controlled-release dosage form of divalproex sodium I: formulation design and in vitro/in vivo investigations.

Divalproex sodium is a narrow therapeutic index drug that is widely used for the treatment of epilepsy, the manic episodes associated with bipolar disorder, and prophylaxis of migraine headaches. The present investigation was undertaken to design an oral dosage form that would provide once-daily administration with improved therapy and to explore the relationships between in vitro drug release and in vivo absorption. Controlled release hydrophilic matrix formulations of divalproex sodium were designed and evaluated via in vitro and in vivo studies. The release rate of divalproex sodium was modulated by varying different rate-controlling hydrophilic polymers and measured in vitro using a USP apparatus II dissolution method. Formulations with differing release rates were studied in beagle dogs and in healthy subjects. A selected formulation given once-daily was further evaluated against the commercial enteric tablet dosed twice-daily in a multiple dose study, and shown to provide desired nearly constant therapeutic plasma concentrations over the entire 24-h dosing interval. Preliminary linear relationships between in vitro dissolution and in vivo absorption were observed in both the animal model and in humans. However, the relationships were formulation dependent, indicating a need for further studies.

Design of pH-independent controlled release matrix tablets for acidic drugs.

The rate and extent of drug release from most controlled release systems are influenced by the pH of the dissolution medium for drugs with pH-dependent solubility. This dependency of drug release on pH may lead to additional inter- and intra-subject variability in drug absorption. In the present study, a pH-independent controlled release matrix system for acidic drugs was designed by incorporating release-modifiers in the formulation. Controlled release matrix tablets were prepared by compression of divalproex sodium, Methocel K4M and Eudragit E 100 or Fujicalin as the release-modifier. For formulations without any release-modifier, the extent and rate of drug release at pH 6.8 was much higher than that at pH 1.0. Formulations containing Eudragit E 100 provided drug release that was essentially independent of pH. This was achieved because Eudragit E 100 significantly increased the drug release in acidic medium and slightly decreased the release rate at higher pH. The increased release in the acidic medium can be attributed to the elevation of the micro-environmental pH in the swollen polymer gel layer. Formulations containing Fujicalin were less effective than those containing Eudragit E 100. This was attributed to the relative inability to elevate the pH and shorter residence time of Fujicalin in the matrix relative to Eudragit E 100.