Time of Intravenous Acetaminophen Administration

The purpose of the study is to examine the effects of timing of administration of
intravenous (IV) acetaminophen and how timing relates to analgesic efficacy as measured by
postoperative pain scores. A maximum of 138 patients meeting inclusion criteria who present
for a scheduled total hip replacement under general anesthesia will be randomized into one
of two arms: 1) the closure group will receive the first dose of one gram of intravenous
acetaminophen administered upon onset of skin closure, 2) the preemptive group will receive
the first dose of one gram of intravenous acetaminophen administered within 60 minutes prior
to incision. Both groups will receive subsequent doses of one gram of intravenous
acetaminophen every 6 hours x 24 hours. The maximum dose in a 24 hour period will not exceed
4 grams according to FDA recommendations.

Inclusion Criteria:

- Patients 30-75 years of age weighing ≥55 kg scheduled for elective total hip
arthroplasty performed under general anesthesia will be included. As determined by
the anesthesia team assigned to the case, eligible patients will also be assigned ASA
physical status of I, II, or III and deemed capable of reporting their perceived pain
using numeric pain scales and capable of operating a patient controlled anesthesia
(PCA) device.

Exclusion Criteria:

- Exclusion criteria include known allergy, hypersensitivity, or contraindication to
acetaminophen, history of alcohol or drug abuse, prisoners, emergency THAs, patients
with chronic malnutrition or a body mass index (BMI) < 18 kg/m2 and non-English
speaking patients. Additional exclusion criteria include impaired liver function
defined as AST and ALT each ≥ twice normal limits and renal dysfunction (creatinine
>2.0 mg/dl).