The kinetics of nifedipine release from porous hydrophilic matrices and the pharmacokinetics in man.

Porous hydrophilic tablets of nifedipine were prepared with hydroxypropyl methylcellulose as swellable polymer, as well as with the addition of a solid dispersion of the drug in polyethylene glycol, a water soluble system. The kinetic data conformed with the Higuchi square root equation and first order release for in vitro release from a single planar surface of the tablet, as well as release from the whole tablet. The addition of a soluble fraction to the porous swellable release system increased the nifedipine release rate constant. This shows that the dosage form may be formulated as a drug-polymer system which exhibits constant release at a desired rate. In the bioequivalence study with five volunteers, the pharmacokinetic parameters of a sustained release hydrophilic tablet of nifedipine and of immediate release capsules were determined. Although the bioavailability of the two preparations is similar, the therapeutic effects may differ. The rate of absorption, the maximum concentration levels, the time of the peak and the period of maintenance of the therapeutic serum levels after single oral doses are different after the administration of the two tested formulations. The hydrophilic tablets of nifedipine may be useful as a sustained release formulation for long term treatment of hypertension.