Today's blinded crossover study tested the efficacy of oxycodone in ten adults suffering from chronic severe pancreatitis pain. Patients in the study were treated with oxycodone, morphine or placebo and then exposed to various types of painful stimuli on their skin, muscle and oesophagus in order to determine any improvement in their pain tolerance threshold. When skin and muscle were exposed to mechanically-evoked pain, oxycodone was significantly better at increasing the pain tolerance threshold of patients compared with morphine or placebo (skin: F=12.4, P<0.001, muscle: F=11.0, P<0.001), and this was similarly true of thermally-evoked pain compared with placebo (skin: F=8.5, P<0.001). Oxycodone also showed benefits with oesophageal stimulation (F=9.5, P<0.001), whereas morphine showed no better efficacy than placebo.
Lead pain researcher, Prof. Dr Arendt-Nielsen, Aalborg University, Denmark commented on the significance of this data; "Treatment of visceral pain, such as that caused by conditions like irritable bowel syndrome, dyspepsia or pancreatitis, is not based on scientific rationale as the studies performed so far have not really looked into the basic pain mechanisms involved in those pain syndromes."
"Management of visceral pain should be based on a fundamental understanding of the unique mechanisms involved, and this evidence suggests opioids such as oxycodone may act differently from morphine, and more efficiently, and hence may be a better treatment option for patients with chronic pancreatitis pain."
The findings from this clinical practice study confirm results of an experimental comparative study of oxycodone and morphine in healthy adults, which suggested for the first time that oxycodone may provide greater analgesic effects for the treatment of severe visceral pain compared with morphine, which provided similar analgesia to placebo. The study concluded that the better analgesic profile of oxycodone in visceral pain was due to its distinct pharmacological profile compared with morphine.
Visceral pain can be very difficult to treat because it appears to cause a rapid sensitisation to stimulation all over the body³. This frequently leads to a condition called allodynia, where normal sensation is perceived by the patient as painful4. By this point, opioids like morphine have traditionally been of little use. The constant irritation of viscera leads to an up-regulation of pain receptors and an associated increase in the -opioid receptor. This accounts for the increased sensitivity to touch and can lead to the inefficacy of morphine, which almost exclusively binds the μ-opioid receptor. It further raises the suggestion that alternative opioid receptor binding profiles may show very different efficacy in these conditions.
Professor Dr Arendt-Nielsen concluded: "Since oxycodone may interact with more and different opioid receptors than morphine receptors, it is vital to examine the efficacy of oxycodone in patients suffering with visceral pain and associated symptoms such as hyperalgesia. These data suggest that opioid actions, such as those activated by oxycodone, are more efficient for treatment of patients with chronic severe visceral pain."
What are Opioids?
For more information on what opioids are, and opioid-induced constipation (OIC), please see:All About Opioids and Opioid-Induced Constipation (OIC)
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About oxycodone
Oxycodone is a full opioid agonist with affinity for mu (µ) and kappa (k) receptors. Its opioid agonist actions are similar to those of other opioid analgesics, primarily affecting the central nervous system and smooth muscle. It is used, in both prolonged-release and immediate-release formulations, across a broad spectrum of moderate to severe cancer and severe non-cancer related pain types such as somatic (e.g. osteoarthritis), neuropathic (e.g. diabetic neuropathy) and visceral (e.g. pancreatitis) pain. As with all pure opioid agonists, there is no ceiling effect to the analgesia seen with oxycodone.
References:
1 - Staahl C et al. Differential effect of opioids in patients with chronic pancreatitis: An experimental pain study. Scandinavian Journal of Gastroenterology 2007;42; (3).
2 - Staahl C et al. A comparative study of oxycodone and morphine in a multi-modal, tissue-differentiated experimental pain model. Pain 2006; 123:28-36.
3 - Cervero F. Visceral pain: mechanisms of peripheral and central sensitization. Annals of Medicine 1995; 27(2):235-9.
4 - Cousins M J. Advances in the long-term management of chronic pain: recent evidence with OROS® hydromorphone, a novel, once-daily, long-acting opioid analgesic. Persistent pain: a disease entity. Journal of Pain Symptom Management 2007; 33 (2 Suppl 1):S4-S10.