No problem. What I was saying is that it's the narcotic that shuts down the GI trak via opioid receptors in the bowel. The trick is to give just enough of an opoioid antagonist to keep the opiod-receptors in the bowel from shutting down while not allowing enough of the opioid receptor to enter the blood stream and counteract the analgesic effect of the narcotic. See, e.g. "Fixed-ratio combination oxycodone/naloxone compared with oxycodone alone for the relief of opioid-induced constipation in moderate-to-severe noncancer pain," Simpson K, Leyendecker P, Hopp M, Müller-Lissner S, Löwenstein O, De Andrés J, Troy Ferrarons J, Bosse B, Krain B, Nichols T, Kremers W, Reimer K, Curr Med Res Opin, 2008 Dec;24(12):3503-12.

Leeds Teaching Hospitals, Leeds, UK.

OBJECTIVE: Opioid therapy is frequently associated with treatment-limiting constipation. Naloxone is an opioid antagonist with low oral systemic bioavailability. This Phase III clinical trial assessed the safety and efficacy of an oral fixed-ratio combination of oxycodone prolonged-release (PR) and naloxone PR compared with oxycodone PR in relieving opioid-induced constipation.

STUDY DESIGN: This double-blind, multicenter trial was conducted in specialist and primary care centers in four European countries in an out-patients setting. The study included 322 adult patients with moderate-to-severe, noncancer pain requiring opioid therapy in a range of >or=20 mg/day and <or=50 mg/day oxycodone. Following a run-in phase patients were randomized to receive oxycodone PR/naloxone PR or oxycodone PR for 12 weeks. The primary outcome was improvement in constipation as measured using the Bowel Function Index (BFI). Secondary/exploratory assessments focused on pain intensity and additional bowel parameters. Trial registration: NCT00412152.

RESULTS: A significant improvement in BFI scores occurred with oxycodone PR/naloxone PR compared with oxycodone PR after 4 weeks of double-blind treatment (-26.9 vs. -9.4, respectively; p < 0.0001), observed after only 1 week of treatment and continued until study end. A significant increase in the number of complete spontaneous bowel movements and decrease in laxative use were also reported. This improvement in bowel function was achieved without compromising the analgesic efficacy of the oxycodone component; pain intensity remained constant throughout the study. The incidence of adverse events was comparable in both groups and consistent with those expected of opioid analgesics. As the study was limited to a dose range of up to 50 mg oxycodone equivalent per day, further research on higher doses would be recommended.

CONCLUSION: The fixed-ratio combination of oxycodone PR/naloxone PR is superior to oxycodone PR alone, offering patients effective analgesia while significantly improving opioid-induced constipation.

PMID: 19032132 [PubMed - indexed for MEDLINE]
http://www.ncbi.nlm.nih.gov/pubmed/1...ubmed_RVDocSum

And for a free full-text online (and quite readable) article on the subject, check out "Patient assessment of a novel therapeutic approach for the treatment of severe, chronic pain," Nadstawek J, Leyendecker P, Hopp M, Ruckes C, Wirz S, Fleischer W, Reimer K, Int J Clin Pract 2008 Aug;62(8):1159-67, at http://www.pubmedcentral.nih.gov/art...medid=18705820

There is another drug out there, Methylnaltrexone (Relistor), which is even better than naloxone where, in any dose, it apparently doesn't effect the analgesic properties of the opioid in question. The problem is that it's currently available only for use via subcutaneous injection, although I've heard that an oral version may be available as early as 2010. See,

"Methylnaltrexone: the answer to opioid-induced constipation?" Cannom RR, Mason RJ, Expert Opin Pharmacother, 2009 Apr;10(6):1039-45:

Opioid-induced constipation is a significant problem particularly for end stage cancer patients, methadone users, patients suffering from chronic pain as well as surgical patients. Until recently, there were few efficacious treatment options that did not have significant side effects. Methylnaltrexone is a promising drug for the treatment of opioid-induced constipation. It is an opioid-receptor antagonist that blocks the peripheral gastrointestinal opioid receptors responsible for opioid-induced bowel dysfunction. Due to the drug's polarity, it does not cross the blood-brain barrier; therefore, it does not block the central opioid receptors, thus, retaining effective analgesia. Methylnaltrexone has been recently approved by the FDA in the subcutaneous form for the treatment of opioid-induced bowel dysfunction, whereas the intravenous and oral forms remain under investigation.

PMID: 19364251 [PubMed - in process]
http://www.ncbi.nlm.nih.gov/pubmed/1...ubmed_RVDocSum

Please note, however, this is a totally separate concept from giving "micro-doses" of an opioid antagonist (1) without the opioid, in order to stimulate the production of endogenous opioids by the body or (2) with smaller amounts of the opioid, the analgesic effect of which is increased or "potentiated" without triggering any side-effect on the GI track, due to the lower opioid dose.

Hope this is helpful.

Mike