Relative bioavailability of four controlled‐release nifedipine products

Four controlled‐release nifedipine products were investigated in two clinical studies. In study 1, 22 healthy male volunteers took part in an open, multiple‐dose, randomized, crossover study to determine the relative bioavailablity of two 10 mg controlled‐release nifedipine tablet (Adalat® Retard, Bayer), administered 12 hourly, and one 20 mg controlled‐release nifedipine tablet (Adalat® Retard, Bayer) administered 12 hourly. In study 2, 24 healthy male volunteers took part in an open, multiple‐dose, randomized, three‐period, crossover study to determine the relative bioavailability of (i) two 30 mg nifedipine gastro‐intestinal therapeutic system (GITS) tablets (Adalat® XL, Bayer) administered once daily; (ii) one 60 mg nifedipine GITS tablet (Adalat® XL, Bayer) administered once daily; and (iii) one 20 mg plus one 10 mg nifedipine controlled‐release tablet (Adalat® Retard, Bayer), administered 12 hourly. In both studies detailed pharmacokinetic data, in particular with respect to the controlled‐release characteristics of the different formulations, were collected. Results of both studies indicate that all nifedipine products investigated are bioequivalent with respect to the extent of absorption of nifedipine. The nifedipine GITS products (Adalat® XL) have better controlled‐release properties than the Adalat® Retard product, and are suitable for once‐a‐day administration. Copyright © 1994 John Wiley & Sons, Ltd.