Patients in the combination treatment arm had average pain scores of 12.6 compared with 15.8 for patients receiving morphine plus placebo. However, this reduction was not statistically significant, Dudgeon and colleagues report.
Dextromethorphan plus morphine also resulted in a reduction in the number of episodes of pain breakthrough requiring additional medication, in nine instances compared with eleven for morphine plus placebo. However, these differences were also not statistically significant.
The total morphine consumed was 550.9 milligrams in the treatment group compared with 597.1 in the placebo group, which also was not a significant difference.
"We had hoped that the combination would have been helpful in improving pain control," Dudgeon acknowledged in an interview with Reuters Health. "Previous animal and limited human studies had suggested that dextromethorphan should have been helpful."
The hypothesis was that dextromethorphan's properties would act synergistically with morphine to increase the opioid's analgesic properties while modulating opioid tolerance.
Side effects, primarily dizziness, were more common with combination treatment, although again, the differences were statistically insignificant.
"The usefulness of the addition of dextromethorphan to opioids was limited in part by its toxicity," Dudgeon commented. Based on the study findings, she told Reuters Health, "personally, I would not use it in cases of intractable pain."
"Each situation is different and therefore there is no one 'best' approach" to the treatment of intractable pain in this patient population, Dudgeon concluded. "Depending on the circumstances, I might try ketamine, methadone or intraspinal opioids" for the terminally ill patient with severe pain.
SOURCE: Journal of Pain and Symptom Management, April 2007.
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