Overall, 12 of 14 placebo-controlled studies found that patientsreceivingIVacetaminophenhadimprovedanalgesia.WhencomparedwithIVparecoxib,IVmetamizol, or oral ibuprofen, IV acetaminophen was found to have similar analgesic outcomes as the active comparator in 7 of the 8 studies. Parecoxib is a cyclo-oxygenase (COX)2-specific anti-inflammatory agent not approved in the U.S.A. Metamizol is a nonsteroidal anti-inflammatory drug removed from the U.S. market in the 1970 sbecause of its side effect profile, particularly agranulocytosis.
In aggregate, the data from 1,464 patients (780 received IV acetaminophen) included in the 16 RCTs indicate that IV acetaminophen is an effective analgesic in a variety of inpatient and ambulatory surgical procedures. The RCTs were of generally high methodological quality, consistent with a recent analysis showing that acute pain studies are not published unless they contain specific statements describing the primary end points, power analysis, and statistical treatment of data from withdrawals, dropouts, and protocol violations.6 However, the heterogeneity in methods and, in particular, the definitions of the primary end points, as well as the variability in IV acetaminophen dosing regimens did not permit a formal meta-analysis with pooling of results. IV acetaminophen use was not associated with increased adverse events compared with placebo within the limited median follow-up duration for the placebo studies analyzed being no longer than 3 days and usually just 1 day. When prescribing IV acetaminophen for surgical pain, attention must be paid to patients at risk for hepatotoxicity.7