Acetaminophen as an adjunct to morphine by patient-controlled analgesia in the management of acute postoperative pain

Anesth Analg. 1998 Aug;87(2):368-72. doi: 10.1097/00000539-199808000-00024.


Opioids play a fundamental role in the management of postoperative pain, but their use is associated with a number of side effects, including nausea and vomiting, sedation, and respiratory depression. Co-administration of a nonopioid has been proposed as a method of reducing opioid intake and minimizing side effects. Sixty-one ASA physical status I and II patients were enrolled in a double-blind, randomized, placebo-controlled, parallel study to investigate the effect of a combination of acetaminophen and morphine after open reduction and internal fixation of acute limb fractures. Patients were randomized to receive either oral acetaminophen (1 g every 4 h) or placebo as an adjuvant to morphine by patient-controlled analgesia (PCA) postoperatively. They were assessed daily for 72 h or until the PCA was discontinued according to standardized guidelines. The outcome variables collected were pain scores (11-point scale), amount of morphine self-administered, duration of PCA use, compliance with study design, incidence of nausea and sedation, and overall patient satisfaction. The acetaminophen group had lower pain scores on Day 1 (2.1 vs 3.3; P = 0.03) and a shorter average duration of PCA use (35.8 vs 45.5 h; P = 0.03). Overall patient satisfaction was also significantly greater in the acetaminophen group (8.7 vs 7.9; P = 0.04). These data suggest that acetaminophen is a useful adjunct to morphine PCA.

Implications: This study assesses the benefit of combining two analgesics for the treatment of postoperative pain. Such a combination improves the quality of pain relief and patient satisfaction.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial

MeSH terms

  • Acetaminophen / administration & dosage*
  • Acetaminophen / adverse effects
  • Acute Disease
  • Administration, Oral
  • Adolescent
  • Adult
  • Aged
  • Analgesia, Patient-Controlled*
  • Analgesics, Non-Narcotic / administration & dosage*
  • Analgesics, Non-Narcotic / adverse effects
  • Analgesics, Opioid / administration & dosage*
  • Analgesics, Opioid / adverse effects
  • Double-Blind Method
  • Female
  • Humans
  • Male
  • Middle Aged
  • Morphine / administration & dosage*
  • Morphine / adverse effects
  • Nausea / chemically induced
  • Pain Measurement
  • Pain, Postoperative / therapy*
  • Patient Satisfaction
  • Postoperative Complications


  • Analgesics, Non-Narcotic
  • Analgesics, Opioid
  • Acetaminophen
  • Morphine