Formulation and pharmacokinetic evaluation of once-daily sustained-released system of nifedipine with solid dispersion and coating techniques.

A novel sustained-release system was developed for poorly water-soluble drugs by applying solid dispersion (SD) technique to improve the solubility. The SD systems composed of polyvinyl pyrrolidone and stearic acid could not control the release of nifedipine. When the above SD granules were coated with ethylcellolulose (EC10, 45 and 100cp), the dissolution rate extended from 16 to 20 h. When the concentration of EC100cp was increased to 4-6 %, the sustained-release formulation F7 and F8 prepared with 4 % EC100cp and 6 % EC100cp, respectively, could control the drug release in a better manner, namely, they could control drug release in the initial hours with a high cumulative amount of drug at 24 h. The mechanism of drug release from F7 and F8 was diffusion coupled with erosion. When immediate-release capsules was orally administered to rabbits, its absorption was very rapid with a short elimination half-life, while a prolonged maintenance of the plasma drug level up to 24 h was obtained for F7 and F8. Furthermore, the oral bioavailability of F7 and F8 was significantly improved. The results suggested that this novel sustained-release system would be a promising system to improve the solubility and sustain the absorption of poorly water-soluble drugs.