The Efficacy of Intravenous Acetaminophen During Perioperative Neurosurgery Period

Inclusion Criteria: * Subject are able to provide informed consent prior to participation in the study * Subjects must be scheduled to undergo elective open craniotomy procedure of \> 2 hour duration * Subjects must be \>18 years old but less than 90 years old * Subjects must have an American Society of Anesthesiologists (ASA) class I-IV * Subjects must have the ability to communicate meaningfully with the investigator staff and read/understand the study procedures and the use of pain scales Exclusion Criteria: * Subjects used opioids or tramadol daily for \>7 days before study medication administration * Subjects had been treated with any of the following within 14 days of surgery: chaparral, comfrey, germander, jin bu huan, kava, pennyroyal, skullcap, St. John's wort, or valerian * Subjects who have a chronic pain condition, significant medical disease or laboratory abnormality that in the investigator's judgment could compromise the subject's welfare * Subjects with known hypersensitivity to opioids, acetaminophen or the inactive ingredients * Subjects with known or suspected history of alcohol or drug abuse or dependence in the previous 2 years prior to the proposed surgery