Acetaminophen has proven to be an important analgesic in the perioperative setting. It is frequently combined with opiates to allow for synergism, or it can be used as a sole analgesic to provide up to 4 hours of relief for moderate pain. While acetaminophen's main role as a multimodal analgesic regimen has been in tablet form as an opioid/acetaminophen combination in the post- anesthesia care unit (PACU), acetaminophen has emerged as an important perioperative analgesic due to FDA approval of an intravenous (IV) formulation (Ofirmev®) in the United States in 2010. While the new intravenous formulation was approved based upon its postoperative effectiveness and safety, there is also an interest in its preoperative use. [12, 13] The benefit IV acetaminophen claims over the oral modality is a 70% higher blood concentration than a single similar dose (1 gram) of oral acetaminophen and a rapid onset with peak blood concentration within 15 minutes of infusion while similar oral doses may take 90 minutes to reach peak plasma concentrations. Many studies have compared the IV formulation of acetaminophen (Ofirmev®) with the oral formulation at the same dose of 1 gram. However, this does not take into account the difference in pharmacokinetics of oral and intravenous formulations. A 15-minute constant infusion of 1 gram acetaminophen resulted in an average plasma concentration of 25.02 μg/ml at the end of the infusion with subsequent decline to approximately 11 μg/ml at 1 hour and 7 μg/ml at 3 hour after the start of infusion. Pain scores were lowest at one hour but remained significantly low for at least three hours. [FDA med review] Moreover, the pharmacokinetics of the immediate release oral formulation of acetaminophen are well-known. The absorption half life for acetaminophen in healthy subjects ranges from 0.06-0.7 hours (8). The relative bioavailability ranges from 85% to 98%. Moreover, it has a low first pass metabolism with a hepatic extraction ratio of 0.11 to 0.37 (9). After oral administration of 1 gram acetaminophen in the immediate release formulation (IR), peak concentrations of acetaminophen in adults ranged from 7.7 to 17.6 μg/mL within 1 hour.