本帖最後由 goodcat1111 於 2009-4-20 10:13 編輯
作者：Janis Kelly
出處：WebMD醫學新聞
April 2, 2009 — 澳洲阿德雷德大學的研究者在報告中表示，長期使用鴉片控制疼痛會增加病患對某些疼痛的敏感度，使用美沙東(methadone)治療藥癮者也有類似的痛覺過敏。
共同作者、Andrew A. Somogyi醫師向Medscape Psychiatry表示，使用鴉片持續控制非惡性疼痛者，有較低的頂點劑量。增加劑量可能會引起更多疼痛，而不會減少疼痛，因此要謹慎地使用鴉片。
他指出，使用美沙東治療鴉片藥癮者，若需急性止痛，所需之鴉片劑量較高，因為有耐受性以及痛覺過敏。
Justin L. Hay醫師等人進行的此一觀察研究發表於3月份的疼痛期刊。
【證據日漸增多】
研究者針對服用美沙東(n = 10)或嗎啡(n = 10)之非癌症慢性疼痛病患，以及那些因為鴉片成癮而使用美沙東者(n = 10)、與一組對照組(n = 10)，比較各組間的疼痛敏感度。
結果變項為痛覺過敏(對正常痛覺刺激的痛覺反應增加)以及觸痛(一般不會造成疼痛的刺激而引起的疼痛)；使用冷壓耐受以及痛覺過敏電子刺激測量這些，使用von Frey毛髮刺激檢測觸痛。
結果顯示，冷壓耐受檢測發現美沙東維持組以及兩組慢性疼痛組都有痛覺過敏，但是電子刺激時則沒有。各組都沒有觸痛。
Somogyi醫師推測，我們並未預期使用嗎啡或美沙東的慢性非癌症疼痛病患會有類似冷壓導致的痛覺過敏。或許這會發生在使用任何鴉片類藥劑的所有病患。
作者寫道，這些結果強化了現有的證據，長期曝露於鴉片會增加對某些類型疼痛的敏感度。他們也指出，就人類來說，痛覺過敏與觸痛無關。
【證據「並非全然鼓勵」】
加州Palo Alto VA健康照護體系的David Clark醫師也研究鴉片引起的痛覺過敏。根據Clark醫師表示，本研究的重要發現之一是，不只有成癮者有這種痛覺過敏，慢性疼痛病患也有，所以這不只是藥物濫用者的問題。
Clark醫師表示，長期使用鴉片會讓病患對疼痛敏感的這個發現，將會限制臨床使用鴉片來控制慢性疼痛，對於成癮治療者也會有疼痛方面的問題。
他表示，有關長期使用鴉片於慢性疼痛的經驗並非全然都是正面的，鴉片引起的痛覺過敏是這種治療成功有限的原因之一。
研究者有關觸痛的資料對臨床和研究都有影響。Clark醫師表示，觸痛在動物研究中，或許是鴉片引起痛覺過敏的最常見特徵。
他指出，作者相當有理由結論表示，長期使用鴉片之後，特定類型的疼痛或許比其他因素更會造成變化。問題是，沒有人知道這些疼痛的模式為何，也不知道哪種可以作為臨床疼痛病患的最佳指標。
Somogyi醫師表示，本研究也點出了有關鴉片相關痛覺過敏的新問題；包括：劑量是否相關、多快發生、何以只有冷壓痛會發生，而電子刺激引發的疼痛卻不會，以及有關的非神經元機轉為何？
作者報告沒有利益衝突。
Long-Term Opioid Use May Increase Sensitivity to Pain
By Janis Kelly
Medscape Medical News
April 2, 2009 — Long-term use of opioids to manage chronic pain increases patients' sensitivity to certain types of pain, and similar hyperalgesia develops with methadone-maintained drug abusers, researchers from the University of Adelaide, in Australia, report.
"There is a low ceiling dose for opioids in the treatment of persistent nonmalignant pain. Increasing doses may be causing more pain, not less pain. So use opioids sparingly," coauthor Andrew A. Somogyi, MD, told Medscape Psychiatry.
"If methadone-managed opioid-dependent patients need acute analgesia, the dose of opioid may need to be much higher due to the well-known phenomenon of tolerance and also hyperalgesia," he added.
The observational study by Justin L. Hay, MD, and colleagues is in the March issue of the Journal of Pain.
Growing Body of Evidence
The investigators compared pain sensitivity in patients with noncancer chronic pain taking either methadone (n = 10) or morphine (n = 10) with those maintained on methadone due to opioid dependence (n = 10) and with a control group (n = 10).
The outcome variables were hyperalgesia (enhanced pain in response to a normally painful stimulus) and allodynia (pain due to a stimulus that does not normally cause pain). These were measured using cold-pressor tolerance and electrical stimulation for hyperalgesia and von Frey hairs–stimulation testing for allodynia.
Results showed that the methadone-maintained group and both of the chronic pain groups were hyperalgesic measured by the cold-pressor test but not measured by electrical stimulation. None of the groups had allodynia.
"We did not expect that chronic noncancer pain patients on morphine or methadone would have similar cold-pressor–induced hyperalgesia. Perhaps it will occur in all patients on any opioid," Dr. Somogyi speculated.
"These results add to the growing body of evidence that chronic opioid exposure increases sensitivity to some types of pain. They also demonstrate that in humans, this hyperalgesia is not associated with allodynia," the authors write.
Evidence "Not Terribly Encouraging"
David Clark, MD, from the Palo Alto VA Health Care System, in California, has also studied opioid-induced hyperalgesia. According to Dr. Clark, "[An] important finding in this study was that not only addicts have this type of sensitization. Chronic-pain patients have it as well, so this problem goes beyond the boundaries of what is unique to drug abusers."
Dr. Clark said the finding that long-term use of opioids might sensitize patients to pain itself suggests factors that could both limit the clinical utility of opioids used to control chronic pain and add to pain problems in those being treated for addiction.
"The emerging experience regarding the long-term use of opioids for chronic pain is not terribly encouraging, and opioid-induced hyperalgesia is 1 explanation for why this therapy might have limited success," he said.
The researchers' data on allodynia have both clinical and research implications. "Allodynia is perhaps the most commonly followed feature of opioid-induced hyperalgesia in animal populations," Dr. Clark said.
"The authors very reasonably conclude that particular types of pain might be more altered than others after long-term opioid use. The trouble is that no one knows which of these pain models might be the best index of anything experienced by a human with clinical pain," he added.
Dr. Somogyi said that this study also raises new questions about opioid-related hyperalgesia. "Is it dose related? How quickly might it start? Why does it occur only for cold-pressor pain and not electrical-stimulation–induced pain? What nonneuronal mechanism might be involved?" he said.
The authors report no conflicts of interest.
J Pain. 2009;10:316-322. |
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