Route of Analgesia and Pain Perception

Source: Schwartz NA, et al. Acad Emerg Med 1999;6:505.

The purpose of this prospective, randomized, double-blind study was to compare the analgesic effects of IM vs. PO placebo. A convenience sample of 77 patients with acute musculoskeletal pain was given 800 mg of ibuprofen in an orange flavored drink. Thirty-nine of the subjects then received a physiologically inactive tablet resembling ibuprofen and the remaining thirty-eight subjects received a physiologically inactive IM injection resembling ketorolac 60 mg. Subjects then rated the intensity of their pain on a 100 mm visual analog scale (VAS) at baseline and 30, 60, 90, and 120 minutes after treatment.

A total of 64 patients completed the study, giving the authors the ability to detect a 20% difference in VAS score between the two groups with 90% power. After two hours, the mean VAS score had decreased from 60 to 26 for the IM group and from 59 to 27 in the PO group. There were no significant differences in the VAS scores at baseline or at each subsequent interval.

Comment by Stephanie Abbuhl, MD, FACEP

I suspect that all of us have thought, at one time or another, that at least some of the benefit from a parenteral analgesic was due to the placebo effect of the perception of a "stronger medication." The authors of this clever, but small, study have provided some initial evidence to refute this commonly held belief. Instinctively, I like this study because it reminds us of our tendency as physicians to think that pain management is more of a subjective game of manipulation than part of objective disease management. We may have again underestimated our patients.

Admittedly, it is possible that larger studies will expose some placebo effect from parenteral analgesia. In addition, there may also be clinically important differences in patient-assigned VAS scores at less than a 20% difference.1 Finally, it is also possible that certain subgroups of patients will gain a significant placebo effect from parenteral analgesics.

Dr. Abbuhl is Medical Director, Department of Emergency Medicine, The Hospital of the University of Pennsylvania; Associate Professor of Emergency Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA.


1. Todd KH, et al. Ann Emerg Med 1996;27:485-489.