Bioavailability of pseudoephedrine and triprolidine from combination and single-ingredient products

The bioavailability of pseudoephedrine and triprolidine from combination and single-ingredient products was evaluated in a randomized, four-way crossover study. Healthy men volunteers received single doses of a tablet containing triprolidine hydrochloride and pseudoephedrine hydrochloride, a syrup containing the same two drugs, and single-ingredient tablets of each drug. Blood samples were collected before each dose and at 13 sampling times over 24 hours for determination of drug concentrations by radioimmunoassay. Observed peak concentration (Cmax), corresponding observed peak time (tmax), area under the plasma drug concentration-time curve from dosing to time infinity (AUC), and the ratio between plasma clearance and extent of bioavailability (CL/F) were determined. Nonlinear regression analysis was used to obtain estimates of lag time for absorption, first-order rate constant for absorption, first-order rate constant for elimination, and ratio between volume of distribution and extent of bioavailability. Data were analyzed for 19 of 20 men entering the study; data were complete for 16 of these. Pseudoephedrine concentrations were significantly different for the combination tablet and the syrup at four sampling times; no significant differences were found between pseudoephedrine concentrations for the combination tablet and single-ingredient tablet. Cmax, tmax, AUC, and CL/F for pseudoephedrine were not significantly different for the three formulations. Triprolidine concentrations at 8 hours were significantly higher for the combination tablet than for the single-ingredient tablet, and tmax for triprolidine was significantly higher for the combination tablet than for the syrup. For both pseudoephedrine and triprolidine, the combination tablet was bioequivalent to the syrup and to the single-drug tablets.