Sodiums channels are important in central and peripheral neuropathic pains. Morphine has no effect but Fentanyl (in Duragesic), Tramadol (in Tramacet), and Sufentanil (10 more potent fentanyl) do. This highlights there is a rationale for switching to a different opioid.
Pain. 2006 Aug 31; [Epub ahead of print]
Tramadol, fentanyl and sufentanil but not morphine block voltage-operated sodium channels.
Haeseler G, Foadi N, Ahrens J, Dengler R, Hecker H, Leuwer M.
Comment – The classic sodium channel blocker is IV lidocaine which has a popularity for central neuropathic pains. Now it is more clear others have some of this effect. If I switch to Fentanyl patches, I gradually add the patches and cut the dose of Morphine. Surprisingly, I have found many prefer a combination of both – an observation Dr. Ramon Jovey mentioned can happen in one of his talks.
I have also found access to Fentanyl patches almost obligatory should the patient have episodes of vomiting (with bad headaches for example). If the patient cannot keep the opioids down, the vomiting worsens – these people need to put a patch on as soon as they start getting nauseated as the patch can take a day to kick in. Getting the drug plan to cover that is another matter…