Bioavailability of pseudoephedrine from controlled release formulations in the presence of guaifenesin in human volunteers.

A multiple-dose bioequivalence study with six healthy human volunteers was conducted. The bioavailability of an experimental controlled release tablet containing pseudoephedrine was compared with a marketed controlled release pseudoephedrine capsule in a three-way crossover study. Plasma samples, collected serially after oral drug administration, were analyzed for pseudoephedrine content using a specific HPLC method with UV detection. The bioavailability parameters, area under the concentration-time curve (AUC), maximum plasma concentration Cmax, and time to peak (Tmax) were obtained from the plasma concentration-time data. Additionally, model independent pharmacokinetic parameters were estimated. Analysis of variance of the data revealed no statistically significant differences between the test and the reference formulation. The presence of guaifenesin in the sustained release tablet did not influence pseudoephedrine bioavailability. The relative bioavailability of the tablet dosage form with respect to the capsule was found to be 100.8%. Classical and Westlake 95% confidence limits as well as the two one-sided t test, proposed by Schuirmann, and the Anderson-Hauck power analysis supported the inference that the two formulations demonstrated comparable bioavailabilty, even in the presence of guaifenesin. Using a non-linear regression program, it was found that the pharmacokinetics of pseudoephedrine followed a simple one-compartment disposition model with no lag time. Additionally, an in vitro-in vivo correlation, based on the estimation of cumulative relative fraction absorbed, was developed between the absorption of pseudoephedrine in humans and the in vitro dissolution time.