Trial Information

Phase 4: A Comparison of Intravenous Administration of Morphine vs. Oxycodone for Postoperative Pain Management Following Laparoscopic Hysterectomy or Myomectomy

Traditionally, a 1:1 ratio in analgesic potency between intravenous morphine and oxycodone
has been presumed (1-2), but one study demonstrated a 3:2 ratio between those drugs (3).
During the last years, several studies indicate that oxycodone has the potential of
mediating pain relief through the kappa-opioid receptor (4-6), and not only on the my-opioid
receptor like most other opioids used in the clinic. Kappa-opioid receptors are widely
distributed in visceral organs, and this may explain why Kalso (3) found less need for
oxycodone compared to morphine in patients undergoing abdominal surgery.

The aim of this study is to investigate whether patients with visceral postoperative pain
need less oxycodone compared to morphine, and whether patients receiving oxycodone
experience better pain relief and less adverse effects compared to patients receiving
morphine.

Before start of surgery, the patients will be tested with PainMatcher, an instrument testing
electrical pain threshold in the skin (7-10), to ensure that both groups have the same pain
threshold before surgery.

References

1. Kalso E. Oxycodone. Journal of Pain & Symptom Management 2005; 29: S47-S56.

2. Silvasti M, Rosenberg P, Seppala T, Svartling N, Pitkanen M. Comparison of analgesic
efficacy of oxycodone and morphine in postoperative intravenous patient-controlled
analgesia. Acta Anaesthesiol Scand 1998; 42: 576-80.

3. Kalso E, Poyhia R, Onnela P, Linko K, Tigerstedt I, Tammisto T. Intravenous morphine
and oxycodone for pain after abdominal surgery. Acta Anaesthesiol Scand 1991; 35:
642-6.

4. Staahl C, Christrup LL, Andersen SD, Arendt-Nielsen L, Drewes AM. A comparative study
of oxycodone and morphine in a multi-modal, tissue-differentiated experimental pain
model. Pain 2006; 123: 28-36.

5. Ross FB, Smith MT. The intrinsic antinociceptive effects of oxycodone appear to be
kappa-opioid receptor mediated. Pain 1997; 73: 151-7.

6. Sandner-Kiesling A, Pan HL, Chen SR, James RL, Haven-Hudkins DL, Dewan DM, Eisenach JC.
Effect of kappa opioid agonists on visceral nociception induced by uterine cervical
distension in rats. Pain 2002; 96: 13-22.

7. Alstergren P, Forstrom J, Alstergren P, Forstrom J. Acute oral pain intensity and pain
threshold assessed by intensity matching to pain induced by electrical stimuli. Journal
of Orofacial Pain 2003; 17: 151-9.

8. Lundeberg T, Lund I, Dahlin L, Borg E, Gustafsson C, Sandin L, Rosen A, Kowalski J,
Eriksson SV. Reliability and responsiveness of three different pain assessments.
Journal of Rehabilitation Medicine 2001; 33: 279-83.

9. Nielsen PR. Prediction of post-operative pain by an electrical pain stimulus. Acta
Anaesthesiol Scand 2007; 51: 582-6.

10. Stener-Victorin E, Kowalski J, Lundeberg T. A new highly reliable instrument for the
assessment of pre- and postoperative gynecological pain. Anesth & Analg 95: 151-7.