The second study involved patients undergoing
breast resection, or mastectomy with or without axillary
resection, with a 1-g dose 20 minutes before the end of
surgery and pain followed for 24 hours (reference 13 in
Table 1). Although no difference in total morphine use
was detected, 42% of IV acetaminophen patients did
not receive any morphine, compared with 4% in
placebo group. The authors also found that 2 of the 13
patients with more extensive surgical procedures (eg,
axillary dissection) that received IV acetaminophen did
not request morphine in the first 24 hours postoperatively,
whereas all placebo patients did. IV acetaminophen
patients did have significantly less pain only at
the 1-hour measurement when compared with placebo,
but from 2 to 24 hours postoperatively, average pain
ratings were below 2.5 in both groups and did not differ