STUDY QUALITY
The RCTs were of generally high methodological quality as measured by the Jadad Scale, with median score = 5 (range 2 to 5). Fifteen of the 22 studies had the highest quality score of 5. All studies except one reported an a priori power analysis.
RCTs WITH AN ACTIVE COMPARATOR
Overall, in 7 of the 8 studies with an active comparator arm (IV parecoxib [n = 3 studies], IV metamizol [n = 4], oral ibuprofen [n = 1]), IV acetaminophen was found to have similar analgesic outcomes as the active comparator. Three of these 8 studies also reported that IV acetaminophen patients had a significant reduction in mean opioid consumption, a lower percentage of patients rescuing (defined as the fraction needing any rescue), or a longer time to first rescue with IV acetaminophen compared with the active comparator patients.
RCTs WITH A PLACEBO CONTROL
Twelve of the 14 placebo-controlled studies found that IV acetaminophen patients had improved analgesia. Ten of the 14 placebo-controlled studies found either a significant reduction in mean opioid consumption or a lower percentage of patients rescuing with IV acetaminophen. One study that had no observed pain difference found that IV acetaminophen patients did need less rescue compared with placebo patients.