Committed to trials of Low Dose Naltrexone as a treatment for autoimmune diseases

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LDN and Pain

Trials and Studies of LDN for Pain.

Dr Pradeep Chopra Link Link


  • Chopra P1,  Cooper MS. , Treatment of Complex Regional Pain Syndrome (CRPS) using low dose naltrexone (LDN)., J Neuroimmune Pharmacol. 2013 Jun;8(3):470-6. doi: 10.1007/s11481-013-9451-y. Epub 2013 Apr 2.


Complex Regional Pain Syndrome (CRPS) is a neuropathic pain syndrome, which involves glial activation and central sensitization in the central nervous system. Here, we describe positive outcomes of two CRPS patients, after they were treated with low-dose naltrexone (a glial attenuator), in combination with other CRPS therapies. Prominent CRPS symptoms remitted in these two patients, including dystonic spasms and fixed dystonia (respectively), following treatment with low-dose naltrexone (LDN). LDN, which is known to antagonize the Toll-like Receptor 4 pathway and attenuate activated microglia, was utilized in these patients after conventional CRPS pharmacotherapy failed to suppress their recalcitrant CRPS symptoms.


  • Santos CM1,  Francischi JN,  Lima-Paiva P,  Sluka KA,  Resende MA. , Effect of transcutaneous electrical stimulation on nociception and edema induced by peripheral serotonin., Int J Neurosci. 2013 Jul;123(7):507-15. doi: 10.3109/00207454.2013.768244. Epub 2013 Mar 15.


Transcutaneous electrical nerve stimulation (TENS) is defined as the application of an electrical current to the skin through surface electrodes for pain relief. Various theories have been proposed in order to explain the analgesic mechanism of TENS. Recent studies have demonstrated that part of this analgesia is mediated through neurotransmitters acting at peripheral sites. The aim of this study was to investigate the effects of low frequency (LF: 10 HZ) TENS and high frequency (HF: 130 HZ) TENS on hyperalgesia and edema when applied before the serotonin (5-HT) administered into the rat paw. LF and HF TENS were applied to the right paw for 20 min, and 5-HT was administered immediately after TENS. The Hargreaves method was used to measure nociception, while the hydroplethysmometer (Ugo Basile®) was used to measure edema. Neither HF nor LF TENS inhibited 5-HT-induced edema. However, LF TENS, but not HF TENS, completely reduced 5-HT-induced hyperalgesia. Pre-treatment of the paw with naltrexone, prior to application of TENS, (Nx: 50 μg; showed a complete blockade of the analgesic effect induced by low frequency TENS. Thus, our results confirmed the lack of an anti-inflammatory effect through the use of TENS as well as the participation of peripheral endogenous opioid receptors in LF TENS analgesia in addition to its central action.


  • Frech T1,  Novak K,  Revelo MP,  Murtaugh M,  Markewitz B,  Hatton N,  Scholand MB,  Frech E,  Markewitz D,  Sawitzke AD. , Low-dose naltrexone for pruritus in systemic sclerosis., Int J Rheumatol. 2011;2011:804296. doi: 10.1155/2011/804296. Epub 2011 Sep 12.


Pruritus is a common symptom in systemic sclerosis (SSc), an autoimmune disease which causes fibrosis and vasculopathy in skin, lung, and gastrointestinal tract (GIT). Unfortunately, pruritus has limited treatment options in this disease. Pilot trials of low-dose naltrexone hydrochloride (LDN) for pruritus, pain, and quality of life (QOL) in other GIT diseases have been successful. In this case series we report three patients that had significant improvement in pruritus and total GIT symptoms as measured by the 10-point faces scale and the University of California Los Angeles Scleroderma Clinical Trials Consortium Gastrointestinal Tract 2.0 (UCLA SCTC GIT 2.0) questionnaire. This small case series suggests LDN may be an effective, highly tolerable, and inexpensive treatment for pruritus and GIT symptoms in Ssc.



To find appropriate and effective treatment options for chronic pain syndromes is a challenging task. Multimodal treatment approach has been gaining acceptance for chronic pain. However, combining treatments, such as acupuncture, with rational pharmacology is still in its infancy. Acupuncture influences the opioid and cannabinoid system through releasing endogenous receptor ligands. Low dose naltrexone also acts on both these systems, and upregulates the opioid and cannabinoid receptors. The authors hypothesise that low dose naltrexone could enhance the pain-relieving effect of acupuncture.


  • Hay JL1,  La Vincente SF,  Somogyi AA,  Chapleo CB,  White JM. , Potentiation of buprenorphine antinociception with ultra-low dose naltrexone in healthy subjects, Eur J Pain. 2011 Mar;15(3):293-8. doi: 10.1016/j.ejpain.2010.07.009. Epub 2010 Aug 21.


Previous reports have demonstrated greater antinociception following administration of a buprenorphine/naloxone combination compared to buprenorphine alone among healthy volunteers. The aim of the current investigation was to determine whether buprenorphine antinociception could be enhanced with the addition of ultra-low dose naltrexone, using a range of dose ratios. A repeated-measures, double-blind, cross-over trial was undertaken with 10 healthy participants. The effects of each buprenorphine:naltrexone ratio (100:1, 133:1, 166:1, and 200:1) on cold pressor tolerance time and respiration were compared to the effects of buprenorphine only. The 166:1 ratio was associated with significantly greater tolerance time to cold pressor pain than buprenorphine alone. Minimal respiratory depression and few adverse events were observed in all conditions. These findings suggest that, as previously described with naloxone, the addition of ultra-low dose naltrexone can enhance the antinociceptive effect of buprenorphine in humans. This potentiation is dose-ratio dependent and occurs without a concomitant increase in adverse effects.


Copyright © 2010 European Federation of International Association for the Study of Pain Chapters. Published by Elsevier Ltd. All rights reserved.


  • Largent-Milnes TM1,  Guo W,  Wang HY,  Burns LH,  Vanderah TW. , Oxycodone plus ultra-low-dose naltrexone attenuates neuropathic pain and associated mu-opioid receptor-Gs coupling., J Pain. 2008 Aug;9(8):700-13. doi: 10.1016/j.jpain.2008.03.005. Epub 2008 May 12.


Both peripheral nerve injury and chronic opioid treatment can result in hyperalgesia associated with enhanced excitatory neurotransmission at the level of the spinal cord. Chronic opioid administration leads to a shift in mu-opioid receptor (MOR)-G protein coupling from G(i/o) to G(s) that can be prevented by cotreatment with an ultra-low-dose opioid antagonist. In this study, using lumbar spinal cord tissue from rats with L(5)/L(6) spinal nerve ligation (SNL), we demonstrated that SNL injury induces MOR linkage to G(s) in the damaged (ipsilateral) spinal dorsal horn. This MOR-G(s) coupling occurred without changing G(i/o) coupling levels and without changing the expression of MOR or Galpha proteins. Repeated administration of oxycodone alone or in combination with ultra-low-dose naltrexone (NTX) was assessed on the SNL-induced MOR-G(s) coupling as well as on neuropathic pain behavior. Repeated spinal oxycodone exacerbated the SNL-induced MOR-G(s) coupling, whereas ultra-low-dose NTX cotreatment slightly but significantly attenuated this G(s) coupling. Either spinal or oral administration of oxycodone plus ultra-low-dose NTX markedly enhanced the reductions in allodynia and thermal hyperalgesia produced by oxycodone alone and minimized tolerance to these effects. The MOR-G(s) coupling observed in response to SNL may in part contribute to the excitatory neurotransmission in spinal dorsal horn in neuropathic pain states. The antihyperalgesic and antiallodynic effects of oxycodone plus ultra-low-dose NTX (Oxytrex, Pain Therapeutics, Inc., San Mateo, CA) suggest a promising new treatment for neuropathic pain. 


The current study investigates whether Oxytrex (oxycodone with an ultra-low dose of naltrexone) alleviates mechanical and thermal hypersensitivities in an animal model of neuropathic pain over a period of 7 days, given locally or systemically. In this report, we first describe an injury-induced shift in mu-opioid receptor coupling from G(i/o) to G(s), suggesting why a mu-opioid agonist may have reduced efficacy in the nerve-injured state. These data present a novel approach to neuropathic pain therapy


  • Hamann S1,  Sloan P. , Oral naltrexone to enhance analgesia in patients receiving continuous intrathecal morphine for chronic pain: a randomized, double-blind, prospective pilot study., J Opioid Manag. 2007 May-Jun;3(3):137-44.



Years' worth of observations suggest that morphine has both inhibitory and excitatory actions, and that selective blockade of excitatory effects by low doses of opioid antagonists (e.g., naltrexone) may paradoxically enhance morphine analgesia. The purpose of this pilot study was to evaluate and compare the analgesic efficacy and safety of two different low doses of oral naltrexone given in addition to chronic intrathecal morphine infusions in patients with chronic nonmalignant pain (CNMP). 


After institutional review board approval, 15 patients with CNMP receiving continuous intrathecal morphine were admitted into a prospective, randomized, double-blind, placebo-controlled, seven-day pilot study. Patients were randomized into three treatment groups based on oral naltrexone dose: 100 microg (Group A, n = 3), 10 microg (Group B, n = 7), or placebo (Group C, n = 5). All patients continued with their constant intrathecal morphine infusion, and in addition they received one capsule of study medication every 12 hours for seven days. Other analgesics or coanalgesics were kept at a constant dose level throughout the study. Patients rated pain scores (visual analogue score [VAS]; 0 = no pain, 10 = worst pain imaginable) and side effects three times daily throughout the study period. Efficacy measures included pain intensity difference (PID) scores, constructed so that positive scores indicate a reduction in pain intensity and negative scores indicate a worsening of pain. 


Fifteen patients (six male, nine female) with a mean (SD) age of 55 (10) years and weight of 81 (21) kg completed the study. The mean (SD) baseline VAS pain intensity rating was similar in all three groups (6.8 [1.5]). Baseline pain VAS score minus the lowest daily pain VAS score yielded the peak PID score. The peak PID score from Day 1 was statistically (p < 0.05) highest (median PID score: 5.9) in Group A compared with Group C. There was a trend in PID scores across Days 2 through 7, with median PID scores higher (i.e., greater pain relief p = 0.07) in Group A. In the daily global pain assessments, the pain scores across Days 2 through 7 approached significance (least pain) in Group A compared to Group C (p = 0.07) or B (p = 0.08). Side effects were common (93 percent of patients), minor (headache, nausea, sedation, dry mouth), and similar across treatment groups. No serious adverse events were observed, and no evidence of opioid withdrawal was seen. 


1) Patients with chronic pain who received oral naltrexone 100 microg BID in addition to their chronic intrathecal morphine infusions demonstrated the greatest improvement (p = 0.07) in their daily pain scores. Because of the small sample size, the results did not reach traditional levels of significance. 2) Side effects were common, minor, and similar across treatment groups. 3) No serious adverse events were recorded. 4) No evidence of opioid antagonist toxicity or opioid withdrawal was observed.  



Oxytrex (Pain Therapeutics, Inc.) is an oral opioid that combines a therapeutic amount of oxycodone with an ultra-low dose of the antagonist naltrexone. Animal data indicate that this combination minimizes the development of physical dependence and analgesic tolerance while prolonging analgesia. Oxytrex is in late-stage clinical development by Pain Therapeutics for the treatment of moderate-to-severe chronic pain. To evaluate the safety and efficacy of the oxycodone/naltrexone combination, three clinical studies have been conducted, one in healthy volunteers and the other two in patients with chronic pain. The putative mechanism of ultra-low-dose naltrexone is to prevent an alteration in G-protein coupling by opioid receptors that is associated with opioid tolerance and dependence. Opioid agonists are initially inhibitory but become excitatory through constant opioid receptor activity. The agonist/antagonist combination of Oxytrex may reduce the conversion from an inhibitory to an excitatory receptor, thereby decreasing the development of tolerance and physical dependence.


  • Abul-Husn NS1,  Sutak M,  Milne B,  Jhamandas K. , Augmentation of spinal morphine analgesia and inhibition of tolerance by low doses of mu- and delta-opioid receptor antagonists., Br J Pharmacol. 2007 Jul;151(6):877-87. Epub 2007 May 14.


Ultralow doses of naltrexone, a non-selective opioid antagonist, have previously been found to augment acute morphine analgesia and block the development of tolerance to this effect. Since morphine tolerance is dependent on the activity of micro and delta receptors, the present study investigated the effects of ultralow doses of antagonists selective for these receptor types on morphine analgesia and tolerance in tests of thermal and mechanical nociception. 

EXPERIMENTAL APPROACH:  Effects of intrathecal administration of mu-receptor antagonists, CTOP (0.01 ng) or CTAP (0.001 ng), or a delta-receptor antagonist, naltrindole (0.01 ng), on spinal morphine analgesia and tolerance were evaluated using the tail-flick and paw-pressure tests in rats. 


Both micro and delta antagonists augmented analgesia produced by a sub-maximal (5 microg) or maximal (15 microg) dose of morphine. Administration of the antagonists with morphine (15 microg) for 5 days inhibited the progressive decline of analgesia and prevented the loss of morphine potency. In animals exhibiting tolerance to morphine, administration of the antagonists with morphine produced a recovery of the analgesic response and restored morphine potency. 


Combining ultralow doses of micro- or delta-receptor antagonists with spinal morphine augmented the acute analgesic effects, inhibited the induction of chronic tolerance and reversed established tolerance. The remarkably similar effects of micro- and delta-opioid receptor antagonists on morphine analgesia and tolerance are interpreted in terms of blockade of the latent excitatory effects of the agonist that limit expression of its full activity.