Absorption study with a dissolution independent drug - acetaminophen

Absorption of acetaminophen has been shown to be dissolution independent in human. Both extent and rate of absorption are important variables in the treatment of pain. The absorption of acetaminophen was studied by using two different acetaminophen tablets Depyretin® manufactured by Veterans Pharmaceutical Plant, Taiwan, and Scanol®, manufactured by Scanpharm, Denmark. Both Scanol and Depyretin, each of 500 mg single dose, were administered orally to sixteen healthy young Chinese males with an one-week washout period in a randomized crossover design. Plasma samples used for acetaminophen measurement were taken prior to drug administration and at various times up to 12 hr subsequent to administration. The plasma samples were measured for acetaminophen concentration by an HPLC method. Values for areas under plasma concentration-time curve (extent of absorption), peak plasma concentration, time to peak concentration (rate of absorption), elimination rate constant, elimination half-life and oral clearance were compared for each preparation. Statistical analyses including ANOVA, power analysis and 90% confidence intervals after logarithmic transformation, showed no significant difference in the rate and extent of acetaminophen absorption between Scanol and Depyretin. Furthermore, in vivo absorption did not significantly correlate with in vitro dissolution performance in water. However, differences between these two formulations both in in vitro dissolution and in vivo absorption were not seen.