A study in healthy volunteers suggests that the use of Oxycodone ( OxyContin ), a synthetic opioid compound, may be better at treating visceral pain than Morphine.

The results, consistent with clinical experience, show for the first time significant differences between Oxycodone and Morphine in the treatment of visceral pain.

" Visceral pain is one of the most challenging symptoms of gastroenterology," explained Jens Arendt-Nielsen, at Aalborg University, Denmark. " This study is the first time that analgesics have been assessed using a multi-modal, multi-tissue pain assessment approach, providing an opportunity to assess the differentiated effect of new and existing drugs on specific tissues and specific pain modalities."

To collect the study results, visceral stimuli were applied to healthy volunteers in the oesophagus via a probe mounted on a balloon. The unique device was used to apply mechanical, heat pain and electrical pain stimuli. For stimulation in skin and muscles, electrodes, a pressure algometer and a 'thermo tester' were used. 24 subjects ( 12 women and 12 men ) participated in this double blind, randomised experiment.

After a baseline recording of the experimental pain, Oxycodone ( 15 mg ), Morphine ( 30 mg ) or placebo were randomly administered. Participants' pain responses were assessed in relation to the different pain stimuli, tested at baseline, 30, 60 and 90 minutes.

Results from the study showed that both opioids had significantly better analgesic effect than placebo ( all P values<.001 ). Most interesting, the opioids were equally effective in all tissues but the viscera, where Oxycodone was shown to be more effective ( P<.001 ).

Visceral pain, classified as pain affecting 'soft' organs and body tissues, or viscera, is an extremely common condition that can be severely debilitating. Most people will have experienced this form of pain, which can range from mild discomfort ( e.g. that associated with indigestion or mild gastro-oesophageal reflux ) to excruciating agony ( e.g. renal colic, severe irritable bowel syndrome etc ).

For many patients, visceral pain can be part of a complex syndrome involving pain signals from a number of organs and tissues - typical of cancer related pain - making it difficult for patients to identify.
Many forms of visceral pain are particularly prevalent in women and are associated with their reproductive system ( period pains, labour pain or postmenopausal pelvic pain ).

Morphine and similar substances ( belonging to the 'opioid' class of medicines ) are often used for the treatment of visceral pain, with Morphine being previously recognised by many physicians as being the first line therapy for treating this condition.
Oxycodone has a long heritage within pain management, having effectively treated millions of patients suffering moderate to severe pain.

Despite the frequent use of opioids to treat visceral pain, however, their effects can be highly variable, due to a range of factors such as daily fluctuations in the pain level, psychological and social factors. In addition, patients often find it difficult to distinguish the pain from the many other symptoms that accompany a particular disease.

Previous experiments in rodents have shown a peripheral effect of k-opioid agonists in visceral pain.
The hypothesis of this experiment was that Oxycodone -- possessing some effect at the k-opioid receptor -- would have a better effect in visceral pain than Morphine, which probably has lesser effect at the k-opioid receptor.

" The results from this experimental study show a difference exists between different types of opioids with regards to their efficacy in the treatment of visceral pain, which is consistent with clinical observations" explained Asbjorn Drewes, Aalborg Hospital, Denmark.

Source : IASP 11th World Congress on Pain, Sydney, 2005


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