Thanks for the appeal, anaesthesiawest is now reactivated.

From the “who would have guessed it” category come the idea of naloxone as an analgesic.

There have been several previous studies (see below) showing that extremely low doses of naloxone appeared to have analgesic properties, but no real explanation of how this might be possible.

The most recent interesting article is this one here, recently published in the journal of pain, showing +(-) naloxone reverses multiple models of chronic neuropathic pain in rats,

http://www.jpain.org/article/S1526-5900(12)00522-6/abstract

Ultra low dose naloxone attenuates morphine tolerance in rats

http://www.sciencedirect.com/science/article/pii/S0091305710001486

Low dose 0.25mcg/kg/hr naloxone reduces opioid consumption, nausea and vomiting in 90 abdominal hysterectomy patients.

The first article showing this was by Gan et al in 1997. They looked at 60 patients who had a PCA along with infusions of varying doses of naloxone or saline. It was designed to look for a reduction in itch and nausea but as well as finding this found the group that got the lowest dose of naloxone also had a reduction in opioid use, with equivalent pain score

http://journals.lww.com/anesthesiology/Abstract/1997/11000/Opioid_sparing_Effects_of_a_Low_dose_Infusion_of.11.aspx