Two of the 14 placebo-controlled studies found no
pain improvement or less opioid use with IV acetaminophen.
One study involved patients undergoing
lumbar discectomy who were administered a single 1-g
dose 45 minutes before the end of surgery and with pain
followed for 2 hours in the post-anesthesia care unit
(PACU) (reference 6 in Table 1). This study also found
no difference between IV acetaminophen and an active
comparator IV parecoxib, whereas IV metamizol
patients had lower pain scores on arrival to PACU with
fewer patients requiring rescue.