Comparative bioavailability of three commercial acetaminophen tablets.

Four different acetaminophen products (three tablets and one liquid) were evaluated for their in vitro properties and in vivo comparative bioavailability. The in vivo properties included assay, hardness, thickness, friability, weight variation, content uniformity, disintegration, and dissolution. A statistically significant variation was observed in friability, disintegration, and dissolution. The dissolution rates were determined in 0.1 N HCl under sink conditions, and the T50% value for Brand A was 50 min while the values for Brands B and C were 1 min. The in vivo evaluation was completed in four subjects with a urinary excretion experiment using a crossover design. The calculated elimination half-lives were 4.12, 2.77, 3.14. amd 2 h for Brands A, B, and C and the standard, respectively. The relative bioavailabilities (with respect to solution) were 82, 87, and 92% for Brands A, B, and C, respectively. The mean amount excreted with Brand A was less than the reference at all time points, although it was not significant. Comparison of the in vitro and in vivo data for the three tablets indicated that the rate and amount of acetaminophen excreted may be related to the dissolution rate.