Multimodal analgesia for postoperative pain may help to reduce opioid use and decrease opioid-associated adverse effects, but is there an opioid-sparing effect with use of intravenous (IV) acetaminophen? A single-center, retrospective, case-control study in Pharmacotherapy assessed 100 patients ≥18 years who underwent knee arthroplasty between January 2012 and March 2013 on the effect of acetaminophen on total opioid use in postoperative patients (primary objective) and the effect of IV acetaminophen on hospital length of stay (secondary objective).

Each dose of IV acetaminophen was administered as a 15-minute infusion either in the operating room or at any time during the perioperative period. Patients in the treatment arm received a mean of three IV acetaminophen doses, with the most common dosing regimens of 1000mg IV once, 1000mg IV every six hours, and 1000mg IV every eight hours. Forty percent of patients in the IV acetaminophen group received only one IV dose.

No statistical significance was observed in total postoperative opioid use between the IV acetaminophen group and the control group, with a total of 135mg oral morphine equivalents in the IV group vs. 112.5mg in the control group. As well, there was no significant difference in daily oral morphine equivalents between the two groups (45mg for IV, vs. 37.5mg for control). Median length of hospital stay for both groups was three days.

While IV acetaminophen did not significantly decrease postoperative opioid use in patients who underwent surgical knee procedures in this study, future research with larger patient populations covering other orthopedic procedures with varying lengths of hospital stays are needed to confirm these results.

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