Intravenous acetaminophen does not reduce morphine use for pain relief in emergency department patients: A multicenter, randomized, double-blind, placebo-controlled trial

BACKGROUND
Pain is one of the main reasons to present to Emergency Departments (EDs). Opioids are indispensable for acute pain management but are associated with side effects, misuse and dependence. The aim of this study was to test whether a single dose of intravenous acetaminophen (paracetamol) can reduce the use of morphine for pain relief and/or morphine-related adverse events.

METHODS
ED patients >18 years with acute pain (i.e. Numerical Rating Scale [NRS] > 4) were screened for eligibility. Patients with analgesia in the last 6 hours, chronic pain or clinical instability were excluded. Patients were randomized in a 1:1 ratio to receive either morphine 0.1 mg/kg and 1 g acetaminophen IV, or morphine 0.1 mg/kg and placebo IV. The intervention was double-blinded. Additional morphine 0.05 mg/kg IV was administered every 15 minutes until pain relief (defined as NRS <4), and if the pain recurred. The primary outcome was the mean morphine dose for pain relief. Secondary outcomes were the total amount of morphine given, time to achieve pain relief and adverse events.

RESULTS
220 patients were randomized and 202 evaluated for the primary outcome. The mean morphine dose for pain relief was similar in both groups (acetaminophen 0.15 mg ± 0.07 mg/kg, placebo 0.16 ± 0.07). There were no differences in the total amount of morphine given (acetaminophen 0.19 ± 0.09 mg/kg, placebo 0.19 ± 0.1 mg/kg) and the time to achieve pain relief (acetaminophen 30 min. [95% CI 17-31], placebo 30 min. [95% CI 30-35]), and the frequency of adverse events (overall 27.4%). Time to pain recurrence did not differ significantly between the groups (HR 1.23 [0.76-1.98], p=0.40).