The effect of guaiphenesin on absorption and bioavailability of paracetamol from composite analgesic preparations.

Using a one compartment pharmacokinetic model with constant rate of availability for absorption, the disposition of paracetamol was compared after administration of Paralen (paracetamol 500 mg in one tablet) with data obtained after administration of two composite analgesic preparations: Guajanal (paracetamol 500 mg, guaiphenesin 200 mg) and Ataralgin (paracetamol 500 mg, guaiphenesin 130 mg, caffeine 70 mg). The combination of paracetamol with guaiphenesin significantly increased the rate of paracetamol absorption availability, most probably by accelerating its transfer from the stomach to the small intestine. The combination with guaiphenesin and caffeine slightly reduced the rate of paracetamol absorption availability but the difference was not statistically significant. The relative bioavailability of paracetamol from the composite analgesic preparations, however, did not show a statistically significant difference as compared to the preparation where paracetamol was present as a single component.