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P T. 2016;41(6): 361, 387
Letter to the Editor

Intravenous Acetaminophen —an Ineffective Analgesic?

Kangwon Song PharmD

To the Editor:

Wang et al. reported in the December 2015 issue of P&T 1 that patients after bariatric surgery administered intravenous (IV) acetaminophen required higher doses of opioids in the postoperative period than patients on opioids alone. We would like to comment on two points necessitating a discussion.

First, the findings of the presented, small, retrospective study (N = 96) are in conflict with several large meta-analyses, including many prospective randomized trials with thousands of patients.24 Possible explanations could include: 1) different bariatric surgical procedures; 2) unchanged opioid prescribing practices after IV acetaminophen was added to the hospital’s formulary; and 3) noncompliance to American Society of Anesthesiologists practice guidelines to schedule acetaminophen and nonsteroidal anti-inflammatory drugs around the clock unless contraindicated.5

Second, Wang et al. did not summarize the four retrospective studies presenting data on a similar patient population (morbidly obese patients undergoing bariatric surgery), including approximately 900 patients, all showing a reduction of opioid consumption in the postoperative period with the addition of IV acetaminophen.69

We believe that it would be more relevant to try to interpret the study results in light of overwhelming high-quality research. We are interested as to why the results of this small study differ from the results of the prior studies. A possible explanation could be bias and methodological deficiencies that are inevitable in a retrospective analysis.


  1. Wang S, Saha R, Shah N, et al. Effect of intravenous acetaminophen on postoperative opioid use in bariatric surgery patients. P T 2015;40;(12):847–850.
  2. Tzortzopoulou A, McNicol ED, Cepeda MS, et al. Single dose intravenous propacetamol or intravenous paracetamol for postoperative pain. Cochrane Database Syst Rev 2011;10CD00712610.1002/14651858.CD007126.pub2
  3. Toms L, Derry S, Moore RA, McQuay HJ. Single dose oral paracetamol (acetaminophen) with codeine for postoperative pain in adults. Cochrane Database Syst Rev 2009;1CD00154710.1002/14651858.CD001547.pub2
  4. McDaid C, Maund E, Rice S, et al. Paracetamol and selective and non-selective non-steroidal anti-inflammatory drugs (NSAIDs) for the reduction of morphine-related side effects after major surgery: a systematic review. Health Technol Assess Winch Engl 2010;14;(17):1–153.iii–iv.10.3310/hta14170
  5. American Society of Anesthesiologists. Standards & guidelines. Available at: Accessed January 20, 2016.
  6. Gonzalez AM, Romero RJ, Ojeda-Vaz MM, Rabaza JR. Intravenous acetaminophen in bariatric surgery: effects on opioid requirements. J Surg Res 2015;195;(1):99–104.10.1016/j.jss.2015.01.004
  7. Saurabh S, Smith JK, Pedersen M, et al. Scheduled intravenous acetaminophen reduces postoperative narcotic analgesic demand and requirement after laparoscopic Roux-en-Y gastric bypass. Surg Obes Relat Dis 2015;11;(2):424–430.10.1016/j.soard.2014.09.017
  8. Song K, Melroy MJ, Whipple OC. Optimizing multimodal analgesia with intravenous acetaminophen and opioids in postoperative bariatric patients. Pharmacother J Hum Pharmacol Drug Ther 2014;34;(suppl 1):S14–S21.10.1002/phar.1517
  9. Ziemann-Gimmel P, Hensel P, Koppman J, Marema R. Multimodal analgesia reduces narcotic requirements and antiemetic rescue medication in laparoscopic Roux-en-Y gastric bypass surgery. Surg Obes Relat Dis Off J Am Soc Bariatr Surg 2013;9;(6):975–980.10.1016/j.soard.2013.02.003