Although the therapeutic range for acetaminophen is not well established, plasma concentrations of 10-20 mcg/ml are associated with antipyretic activity, and previous work has assumed that antipyretic and analgesic doses will be similar. (3-4). However, another study developed two compartmental pharmacokinetic/pharmacodynamic models to relate plasma concentration to pain score relationship in children who received oral acetaminophen 30 minutes before outpatient tonsillectomy. The model demonstrated only a one point decrease in pain score when the concentration increased from 10 μg/mL to 20 μg/mL and a steep loss of pain protection when the concentration fell below 6 - 7 μg/mL. Therefore, this study indicates a saturation of the analgesic effect of acetaminophen at a threshold plasma concentration of as low as 7 μg/mL.