Bioavailability of dyphylline and dyphylline-guaifenesin tablets in humans

A six-way-crossover bioavailability study was conducted with twelve healthy male volunteers to evaluate the relative bioavailability of three tablet formulations containing dyphylline and three tablet formulations containing dyphylline-guaifenesin. Each subject was administered two tablets of each product with greater than or equal to 3 d separating each dose. Blood samples were obtained just prior to each dose and at 0.25, 0.5, 0.75, 1.0, 1.5, 2.0, 3.0, 4.0, 6.0, 8.0, and 10.0 h following each dose. An HPLC method was used to assay dyphylline in the serum. The mean tmax ranged from 0.6 to 1.0 h for the six products. The mean values for Cmax differed by 29%, and the AUC values differed by less than 8%. It was noted that the dyphylline-guaifenesin products exhibited a lower bioavailability than the products which only contained dyphylline. It was concluded that the three combination products were bioequivalent, as were the three dyphylline products.