Comparison of the efficacy and safety of dual-opioid treatment with morphine plus oxycodone versus oxycodone/acetaminophen for moderate to severe acute pain after total knee arthroplasty

44 patients who underwent either TKA or THA (31 of whom completed the study) were randomized to receive either a fixed dose of morphine/oxycodone, a flexible dose of morphine/oxycodone or oxycodone/acetaminophen to compare the efficacy of these analgesic treatments. Results indicated that the morphine/oxycodone flexible dose group experienced a 20% decrease in the time-weighted sum of pain intensity difference from 0 to 48 hours (SPID-48) and 3 times less moderate to severe adverse gastrointestinal events when compared to the oxycodone/acetaminophen group.