Enriched enrollment randomized double-blind placebo-controlled cross-over trial with phenytoin cream in painful chronic idiopathic axonal polyneuropathy (EPHENE): a study protocol

Background

Patients with chronic idiopathic axonal polyneuropathy (CIAP) can have neuropathic pain that significantly impacts quality of life. Oral neuropathic pain medication often has insufficient pain relief and side effects. Topical phenytoin cream could circumvent these limitations.

The primary objectives of this trial are to evaluate (1) efficacy in pain reduction and (2) safety of phenytoin cream in patients with painful CIAP. The main secondary objective is to explore the usefulness of a double-blind placebo-controlled response test (DOBRET) to identify responders to sustained pain relief with phenytoin cream.

Methods

This 6-week, enriched enrollment randomized double-blind, placebo-controlled triple cross-over trial compares phenytoin 20%, 10% and placebo cream in 48 participants with painful CIAP. Enriched enrollment is based on a positive DOBRET in 48 participants who experience within 30 minutes ≥2 points pain reduction on the 11-point numerical rating scale (NRS) in the phenytoin 10% cream applied area and ≥1 point difference in pain reduction on the NRS between phenytoin 10% and placebo cream applied area, in favour of the former. To explore whether DOBRET has predictive value for sustained pain relief, 24 DOBRET-negative participants will be included.

An open-label extension phase is offered with phenytoin 20% cream for up to one year, to study long-term safety.

The main inclusion criteria are a diagnosis of CIAP and symmetrical neuropathic pain with a mean weekly pain score of ≥4 and <10 on the NRS.

The primary outcome is the mean difference between phenytoin 20% versus placebo cream in 7-day average pain intensity, as measured by the NRS, over week 2 in DOBRET positive participants.

Key secondary outcomes include the mean difference in pain intensity between phenytoin 10% and phenytoin 20% cream, and between phenytoin 10% and placebo cream. Furthermore, differences between the 3 interventions will be evaluated on the Neuropathic Pain Symptom Inventory, EuroQol EQ5-5D-5L, and evaluation of adverse events.

Discussion

This study will provide evidence on the efficacy and safety of phenytoin cream in patients with painful CIAP and will give insight into the usefulness of DOBRET as a way of personalized medicine to identify responders to sustained pain relief with phenytoin cream.

Trial registration

ClinicalTrials.gov NCT04647877. Registered on 1 December 2020.

No Detectable Phenytoin Plasma Levels After Topical Phenytoin Cream Application in Chronic Pain: Inferences for Mechanisms of Action

Purpose

Topical phenytoin can act as an analgesic in chronic pain, but it is unclear if topical phenytoin gives rise to systemic side effects. Therefore, the aim of this study is: 1) to evaluate safety in chronic pain patients who used topical phenytoin up to 30% applied daily on intact skin and mucous membrane, through determining phenytoin plasma levels; and 2) to elaborate on the analgesic mechanism of action.

Patients and Methods

In this retrospective study, we collected demographic and clinical data from 33 chronic pain patients who used 10% to 30% phenytoin cream, and in whom blood samples were drawn for phenytoin concentration measurement between January 2017 until September 2020. The instruction was to withdraw blood 1 to 4 hours after the last topical phenytoin application. The primary outcome was the detectability of plasma phenytoin after daily use of topical phenytoin.

Results

Blood withdrawal was carried out after on average 14 treatment days with topical phenytoin and on average 2.5 hours after topical phenytoin application. The median daily applied amount of phenytoin cream was 1.2 grams, resulting in a median daily amount of 120 mg phenytoin on the skin. Phenytoin levels were below the limit of detection in all patients and no side effects were reported.

Conclusion

Plasma phenytoin levels were below the limit of detection after topical use of phenytoin cream formulations up to 30% on intact skin and mucous membrane for the treatment of chronic pain, without side effects emerging. This finding suggests that the mechanism of analgesic action resides in the skin.

Usefulness of a Double-Blind Placebo-Controlled Response Test to Demonstrate Rapid Onset Analgesia with Phenytoin 10% Cream in Polyneuropathy

Purpose

Topical analgesics are an upcoming treatment option for neuropathic pain. In this observational study, we performed a double-blind placebo-controlled response test (DOBRET) in patients with polyneuropathy to determine the personalized analgesic effect of phenytoin 10% cream.

Patients and Methods

In a double-blind fashion, 12 consecutive adult patients with symmetrical painful polyneuropathy and equal pain intensity of ≥4 on the 11-point numerical rating scale (NRS) applied phenytoin10% cream on one painful area and a placebo cream on the corresponding contralateral area. We defined responders as patients who experienced a pain reduction ≥2 NRS points from baseline and ≥1 NRS point difference in pain reduction in favour of phenytoin 10% cream compared with placebo cream within 30 minutes after application. We also evaluated the percentage of pain reduction and frequency of 30% and 50% pain relief from baseline.

Results

Six patients (50%) were responders. Compared with placebo cream, pain reduction was higher in phenytoin 10% cream-applied areas with mean difference in pain reduction of 1.3 (95% CI: 1.1 to 1.8; p<0.001) on the NRS and mean percentage difference in pain reduction of 22% (95% CI: 13% to 32%; p =0.03). All responders had at least 30% pain reduction, and 4 out of 6 had at least 50% pain reduction in the phenytoin 10% cream applied area. All non-responders had less than 30% pain reduction. No side effects were reported.

Conclusion

A DOBRET is easy to perform, quickly identifies an analgesic effect in responders and could be a useful tool to personalize neuropathic pain treatment with topical formulations.

Phenytoin Cream for the Treatment of Sciatic Pain: Clinical Effects and Theoretical Considerations: Case Report

Chronic sciatic pain is difficult to treat. Patients often suffer from considerable pain and are severely hampered in their everyday activities. Most pharmacologic analgesic treatments have disappointing effects, and often are limited due to adverse events. New treatments are therefore needed. Surprisingly we found fast pain reduction after applying topical phenytoin cream at the painful dermatome in a 55-year-old patient suffering from sciatic pain due to pathology of a disc. This patient was treatment resistant for 13 years. Prescribing topical analgesic cream seemed to us at first sight quite counter-intuitive. The clear response in a treatment-resistant patient however provoked us to look deeper in the pathophysiology of sciatic nerve impingement. Recently it has been documented that proximal nerve lesions are followed by small fiber pathology in the skin. This might be a responsible peripheral wind-up generator for the chronification of pain in sciatic nerve compression. Topical application of the broad-acting voltage-gated sodium channel blocker phenytoin could reduce neuropathic pain in our case completely, supporting a peripheral mechanism of action for phenytoin cream in sciatic pain.

Rediscovery of Ceruletide, a CCK Agonist, as an Analgesic Drug

Ceruletide (CRL) is a decapeptide, originating from the skin of a tropical frog, and is many times more potent that cholecystokinin (CCK) in a number of assays. The compound was first isolated and characterized around 50 years ago, and its analgesic properties were subsequently identified. Since the 1980s it has been available in the clinic as a parenteral solution and is used as a diagnostic tool to characterize pancreas and gall bladder malfunctions. Its analgesic properties were evaluated in a number of indications: cancer pain, burns, colic pains and migraine. Preclinically, CRL reduces pain in low microgram dose range and promotes clear and long-lasting analgesic activity in nanograms when applied centrally. CCK is amongst the most widely expressed neuropeptides in the brain. CCK-induced analgesic effects in response to persistent and inflammatory pain have recently been associated with CCK2 receptor signaling. CRL, a potent CCK agonist, might be worthwhile to rediscover as a putative analgesic drug and could represent a potential analgesic intrathecal strategy to patients with cancer-related pain.

Ethical justification of single-blind and double-blind placebo-controlled response tests in neuropathic pain and N-of-1 treatment paradigm in clinical settings

At our center in the Netherlands, patients, who very often are treatment resistant to the analgesics recommended in the guidelines, suffering from symmetrical peripheral neuropathic pain are treated exclusively. We have developed a number of compounded topical formulations containing classical co-analgesics such as ketamine, baclofen, amitriptyline, and phenytoin for the treatment of neuropathic pain in treatment-resistant patients. In order to identify putative responders and exclude an (initial) placebo-response, we developed single-blind and double-blind placebo-controlled response tests. The test can be performed when the patient has a symmetrical polyneuropathy with a pain score difference of not more than 1 point on the 11-point numerical rating scale (NRS) between bilateral pain areas. On one area (eg, left foot) the placebo cream and on the other area (eg, right foot) the active cream will be applied. Within a time frame of 30 minutes, patients are considered responders if they rate a pain difference of at least 2 points on the NRS between the bilateral areas on which the active cream and placebo cream are applied. Response tests can be easily conducted during the first consultation. In this paper, we explore the ethical context of using a placebo in clinical practice in a single-blind and double-blind fashion to improve and individualize treatment of neuropathic pain outside a context of a formal clinical trial.

Rediscovery of old drugs: the forgotten case of dermorphin for postoperative pain and palliation

The repurposing of old drugs for new indications is becoming more accepted as a cost-efficient solution for complicated health problems. However, older drugs are often forgotten when they are not repositioned. This analysis makes a case for re-exploration of dermorphin for intrathecal use in postoperative pain and in a palliative context, with the goal of re-establishing this compound. Dermorphin was isolated from the skin of an Amazonian frog, characterized and identified as a bioactive heptapeptide by Vittorio Erspamer’s research group in the early 1980s. It was traditionally called “Kambo” or “Sapo” by Amazon tribes and was used to improve their physical and psychic skills as hunters. Its structure is rather enigmatic, containing a D-amino acid, and its pharmacological activity in a number of assays was found to be quite impressive and superior to morphine. Moreover, it has been established as more selective and potent with long-lasting analgesia compared to morphine after intracerebroventricular administration in animal models. In 1985, the first clinical trial results of a randomized, placebo-controlled study in postoperative pain were reported, and dermorphin administered via the intrathecal route was again impressively superior over the placebo and the reference compound morphine. This milestone study was apparently minimally read by clinicians, as the study has never been referenced; only 15 pharmacological and review papers after 1985 mentioned the results, with not one being a clinical paper. The interest in dermorphin decreased after 1985, and the compound was never again introduced in the clinical setting. Considering the enormous pressure to find superior acting opioids, this is quite puzzling. We suggest new clinical studies to further evaluate the safety and efficacy of dermorphin, especially administered via the intrathecal route in postoperative pain or for palliative use in terminal patients.

Single-Blind Placebo-Controlled Response Test with Phenytoin 10% Cream in Neuropathic Pain Patients

Background: Phenytoin cream applied topically has been explored in neuropathic pain conditions. In several case series, phenytoin 5% and 10% cream could reduce pain in a clinically relevant way with a fast onset of action within 30 min, and with positive effects on sleep. Objective: To evaluate a single-blind placebo-controlled response test (SIBRET) for use in clinical practice. Materials and Methods: Patients with localized neuropathic pain, having an equal pain intensity in at least 2 areas (e.g., both feet), and a pain intensity of at least 4 on the 11-point numerical rating scale (NRS), were selected to perform the SIBRET. In one area, placebo cream consisting of the base cream was applied, and on the other area, phenytoin 10% cream was applied with separate hands to avoid contamination. Responders were defined as patients who experienced within 30 min at least 2-points difference as scored on the NRS, between the phenytoin 10% and the placebo cream applied areas, in favor of the former. Responders were subsequently prescribed phenytoin 10% cream. Results: Of the 21 patients, 15 patients (71.45%) were classified as responders. The mean pain reduction after 30 min as measured with the NRS in the phenytoin 10% cream area was 3.3 (SD: 1.3) and in the placebo cream area 1.2 (SD: 1.1). The difference of the mean percentage pain reduction between phenytoin 10% cream and placebo cream was 33.2% (SD: 17.6, p < 0.001). Using a 50% reduction on the NRS as a full response criterion, we could identify 57.1% of responders on phenytoin 10% cream and only 9.5% responders on placebo cream. Conclusions: The SIBRET helps patients and clinicians to quickly identify the appropriate treatment and can thus be seen as an important contributor to the domain of personalized medicine in pain. These results can also be regarded as a proof of principle for the analgesic activity of 10% phenytoin cream.

The retinoprotective role of phenytoin

Phenytoin is a non-sedative barbiturate derivate and has been recently rediscovered as a neuroprotective and retinoprotective compound in patients affected by optic neuritis secondary to multiple sclerosis. However, currently there are still no neuroprotective compounds registered and available in the clinic. We reviewed the literature supporting the retinoprotective properties of phenytoin and analyzed the various approaches and definitions from the first research periods onwards. The retinoprotective role of phenytoin was already known in the 1970s, but only recently has this effect been rediscovered, confirming that it could indeed provide structural protection of the retinal cells.

Phenytoin Cream for the Treatment for Neuropathic Pain: Case Series

BACKGROUND: Neuropathic pain can be disabling, and is often difficult to treat. Within a year, over half of all patients stop taking their prescribed neuropathic pain medication, which is most probably due to side effects or disappointing analgesic results. Therefore, new therapies are needed to alleviate neuropathic pain. As such, topical analgesics could be a new inroad in the treatment of neuropathic pain. In 2014, we developed a new topical formulation containing either phenytoin or sodium phenytoin. After optimization of the formulation, we were able to reach a 10% concentration and combine phenytoin with other co-analgesics in the same base cream. OBJECTIVE: To describe a series of 70 neuropathic pain patients who were treated with phenytoin cream. MATERIAL AND METHODS: Cases treated with phenytoin 5% or 10% creams were gathered. The mean onset of pain relief, the duration of effect, and reduction in pain intensity measured on the 11-point numerical rating scale (NRS) were all studied. A single-blind response test with phenytoin 10% and placebo creams was conducted on 12 patients in order to select responders prior to prescribing the active cream. Plasma phenytoin concentrations were measured in 16 patients. RESULTS: Nine patients applied phenytoin 5% cream, and 61 patients used phenytoin 10% cream. After grouping the effects of all of the patients, the mean onset of pain relief was 16.3 min (SD: 14.8), the mean duration of analgesia was 8.1 h (SD: 9.1), and the mean pain reduction on the NRS was 61.2% (SD: 25.0). The mean pain reduction on the NRS while using phenytoin cream was statistically significant compared with the baseline, with a reduction of 4.5 (CI: 4.0 to 5.0, p < 0.01). The 12 patients on whom a single-blind response test was performed experienced a statistically significant reduction in pain in the area where the phenytoin 10% cream was applied in comparison to the area where the placebo cream was applied (p < 0.01). Thirty minutes after the test application, the mean pain reduction on the NRS in the areas where the phenytoin 10% cream and the placebo cream were applied was 3.3 (CI: 2.3 to 4.4, p < 0.01) and 1.1 (CI: 0.4 to 1.9, p < 0.05), respectively. In all 16 patients, the phenytoin plasma levels were below the limit of detection. So far, no systemic side effects were reported. Two patients only reported local side effects: a transient burning aggravation and skin rash. CONCLUSION: In this case series, the phenytoin cream had reduced neuropathic pain considerably, with a fast onset of analgesic effect.

Fundamentals of and Critical Issues in Lipid Autacoid Medicine: A Review

The identification of a number of families of lipid signal molecules since the 1990s created new therapeutic possibilities for a great number of disorders characterized by chronic inflammation and pain. These lipid autacoids have been explored in a great variety of animal models related to inflammation, pain, (neuro-)protection, and repair. Based on the data from these models, as well as on a number of proof of principle studies in the clinic in indications such as neuropathic pain, a new chapter in medicine is about to begin. We would like to introduce the term “Autacoid Pain Medicine” for this chapter. There are, however, a number of methodological and strategic issues to overcome in this field. One of the roadblocks is related to patent strategies around families of these molecules. As this is not always recognized we will present a number of examples.

Phenytoin: neuroprotection or neurotoxicity?

Phenytoin is an 80-year young molecule and new indications are still emerging. The neuroprotective potential of phenytoin has been evaluated for decades. Recently, a positive phase II trial supported its further development in the treatment of optic neuritis in multiple sclerosis. In 1942, however, peripheral neuritis was first reported to be an adverse event of phenytoin, and since then a small but steady stream of publications discussed peripheral polyneuropathy as being a possible adverse event of phenytoin. We have reviewed the literature and concluded there is some supportive evidence for a reversible polyneuropathy after the oral use of phenytoin, though with no evidence for clear neurotoxicity on the level of peripheral nerves. This is probably due to the fact that the pharmacological effects of phenytoin, based on the stabilizing effect of the voltage-gated sodium channels, make impairment of nerve conduction in asymptomatic and symptomatic reversible polyneuropathies plausible. Clear toxically-induced phenytoin-related polyneuropathies, however, are extremely rare and are always related to high dose or high plasma levels of phenytoin, mostly developing during many years of therapy. We could only find one case of a probable reversible chronic phenytoin intoxication resulting in a biopsy proven axonal atrophy with secondary demyelination and signs of remyelination. All case series and case reports published are insufficient in detail to prove a clear causal relation between phenytoin intake and the induction of a peripheral polyneuropathy. Phenytoin does not lead to irreversible toxicity of the peripheral nerves and might, on the other hand, have neuroprotective properties.

Bottlenecks in the development of topical analgesics: molecule, formulation, dose-finding, and phase III design

Topical analgesics can be defined as topical formulations containing analgesics or co-analgesics. Since 2000, interest in such formulations has been on the rise. There are, however, four critical issues in the research and development phases of topical analgesics: 1) The selection of the active pharmaceutical ingredient. Analgesics and co-analgesics differ greatly in their mechanism of action, and it is required to find the most optimal fit between such mechanisms of action and the pathogenesis of the targeted (neuropathic) pain. 2) Issues concerning the optimized formulation. For relevant clinical efficacy, specific characteristics for the selected vehicle (eg, cream base or gel base) are required, depending on the physicochemical characteristics of the active pharmaceutical ingredient(s) to be delivered. 3) Well-designed phase II dose-finding studies are required, and, unfortunately, such trials are missing. In fact, we will demonstrate that underdosing is one of the major hurdles to detect meaningful and statistically relevant clinical effects of topical analgesics. 4) Selection of clinical end points and innovatively designed phase III trials. End point selection can make or break a trial. For instance, to include numbness together with tingling as a composite end point for neuropathic pain seems stretching the therapeutic impact of an analgesic too far. Given the fast onset of action of topical analgesics (usually within 30 minutes), enrichment designs might enhance the chances for success, as the placebo response might decrease. Topical analgesics may become promising inroads for the treatment of neuropathic pain, once sufficient attention is given to these four key aspects.

Topical phenytoin for the treatment of neuropathic pain

We developed and tested a new putative analgesic cream, based on the anticonvulsant phenytoin in patients suffering from treatment refractory neuropathic pain. The use of commercial topical analgesics is not widespread due to the facts that capsaicin creams or patches can give rise to side effects, such as burning, and analgesic patches (e.g., lidocaine 5% patches) have complex handling, especially for geriatric patients. Only in a few countries, compounded creams based on tricyclic antidepressants or other (co-)analgesics are available. Such topical analgesic creams, however, are easy to administer and have a low propensity for inducing side effects. We, therefore, developed a new topical cream based on 5% and 10% phenytoin and described three successfully treated patients suffering from neuropathic pain. All patients were refractory to a number of other analgesics. In all patients, phenytoin cream was effective in reducing pain completely, without any side effects, and the tolerability was excellent. The onset of action of the phenytoin creams was within 30 minutes. Phenytoin cream might become a new treatment modality of the treatment of neuropathic pain.

EMA401: an old antagonist of the AT2R for a new indication in neuropathic pain

EMA401 is an old molecule, synthesized by Parke-Davis in the last century and characterized at that time as an AT2R antagonist. Professor Maree Smith and her group from the University of Queensland (Australia) patented the drug and many related derivatives and other compounds with high affinity for the AT2R for the indication neuropathic pain in 2004, an example of drug repositioning. After some years of university work, the Australian biotech company Spinifex Pharmaceuticals took over further research and development and characterized the S-enantiomer, code name EMA401, and related compounds in a variety of animal models for neuropathic and cancer pain. EMA401 was selected as the lead compound, based on high selectivity for the AT2R and good oral bioavailability (33%). EMA401, however, was only administered once in a chronic neuropathic pain model, and no data have been published in other pain models, or during steady state, although such data were available for the racemate EMA400 and some related compounds (EMA200, EMA400). A pilot phase IIa study demonstrated the efficacy and safety of the drug taken twice daily as two capsules of 50 mg (400 mg/day). In 2015, Novartis took over the clinical development. Two phase IIb studies designed by Spinifex Pharmaceuticals were put on hold, probably because Novartis wanted to improve the clinical design or collect additional preclinical data. Further data are eagerly awaited, especially since EMA401 is first-in-class in neuropathic pain.

NS1209/SPD 502, A Novel Selective AMPA Antagonist for Stroke, Neuropathic Pain or Epilepsy? Drug Development Lessons Learned

Preclinical Research The selective AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor antagonist, NS1209 (also known as SPD 502) has been explored in several research and development campaigns since its selection as a lead drug candidate in the early 1990s by the Danish biotechnology company, NeuroSearch. The compound was successively tested in animal models of stroke, neuropathic pain and epilepsy. The preclinical data to support development for the treatment of stroke were incomplete, as the compound was administered after the stroke episode, and did not protect subcortical areas of the brain. Preclinical data for neuropathic pain and epilepsy appeared more promising, but the design of the Phase IIa studies in both indications was suboptimal, and an exploratory study in neuropathic pain, like one in refractory epilepsy gave inconclusive results. Preclinical data in pain models were much less convincing than reported by the authors in abstract and discussion sections. Due to a long preclinical sequential testing phase and insufficiently powered clinical trials, NS 1209 disappeared from the CNS development pipeline, while its patent protection exclusivity was markedly reduced due to the unfortunate slow speed in development-a phenomenon far from unusual in CNS drug discovery. NeuroSearch ceased operations as an R&D entity in 2012 and its R & D portfolio was transferred to Teva Pharmaceuticals and to a spin off, Saniona A/S. Based on an in-depth case analysis of the development of NS 1209, a number of recommendations are given to reduce chances of failure during clinical development of neuropathic pain compounds and, more generally, of CNS compounds. Drug Dev Res 78 : 75-80, 2017. © 2017 Wiley Periodicals, Inc.

Phenytoin: 80 years young, from epilepsy to breast cancer, a remarkable molecule with multiple modes of action

In 1908 phenytoin (5,5-diphenylhydantoin) was first synthesized as a barbiturate derivative in Germany by professor Heinrich Biltz (1865-1943) and subsequently resynthesized by an American chemist of the pharmaceutical company Parke-Davis in 1923 in Detroit. Screening phenytoin did not reveal comparable sedative side effects as barbiturates and, thus, Parke-Davis discarded this compound as a useful drug. In 1936, phenytoin's anticonvulsive properties were identified via a new animal model for convulsive disorders, developed by Putnam and Merritt, who also evaluated its clinical value in a number of patients in the period 1937-1940. For many diseases, mechanism of action of phenytoin remains obscure. The voltage-gated sodium channel was and is generally regarded as the main target to explain phenytoin's activity as an anticonvulsant and an anti-arrhythmic drug. This target, however, does not explain many of the other clinical properties of phenytoin. We will explore a number of original articles on phenytoin published in its 80 years history and give extra attention to the various hypothesis and experiments done to elucidate its mechanisms of action. Phenytoin has been explored in over 100 different disorders; the last two promising indications tested in the clinic are breast cancer and optic neuritis. Most probably, there are multiple targets active for these various disorders, and the insight into which targets are relevant is still very incomplete. It is remarkable that many pharmacological studies tested one dose only, mostly 50 or 100 μM, doses which most probably are higher than the non-plasma bound phenytoin plasma levels obtained during treatment.

Skin matters! The role of keratinocytes in nociception: a rational argument for the development of topical analgesics

Treatment of neuropathic pain using topical formulations is still in its infancy. Only few topical analgesic formulations have become available for clinical use, and among these, analgesic creams are still rare. This is unfortunate because analgesic creams offer a number of advantages over patches, such as convenience, ease of adapting the frequency of application, and dose, and “rubbing cream where it hurts” involves the patient much more in the therapeutic process compared to patches and other localized treatment modalities. Although the literature supporting the efficacy and safety of analgesic creams (mostly compounded) is growing since the last decade, most pain physicians have not yet noticed and appreciated the therapeutic potential and clinical value of these creams. This is most probably due to a prejudice that topical application should need to act transdermally, more or less as a slow-release formulation, such as in patches delivering opioids. We will discuss this prejudice and show that there are multiple important targets in the skin to be reached by topical analgesic or anti-inflammatory compounds, and that the keratinocyte is one of those targets. By specifically targeting the keratinocyte, analgesia seems possible, effective, and safe, and thus topical analgesic creams may hold promise as a novel treatment modality for neuropathic pain.

Resolvins and aliamides: lipid autacoids in ophthalmology - what promise do they hold?

Resolvins are a novel class of lipid-derived endogenous molecules (autacoids) with potent immunomodulating properties, which regulate the resolution phase of an active immune response. These modulating factors are locally produced, influencing the function of cells and/or tissues, which are produced on demand and subsequently metabolized in the same cells and/or tissues. This review is focused on certain lipid autacoids with putative relevance for ophthalmology in general and for dry eye more specifically. We also briefly investigate the concept of aliamides and the role of palmitoylethanolamide in ophthalmology, and analyze in more detail the putative role and the preclinical and clinical development of resolvins as emerging treatments for dry eye and related disorders, with a focus on one of the lead resolvin derivatives – RX-10045.

Palmitoylethanolamide, a neutraceutical, in nerve compression syndromes: efficacy and safety in sciatic pain and carpal tunnel syndrome

Palmitoylethanolamide (PEA) is an endogenous lipid modulator in animals and humans, and has been evaluated since the 1970s as an anti-inflammatory and analgesic drug in more than 30 clinical trials, in a total of ~6,000 patients. PEA is currently available worldwide as a nutraceutical in different formulations, with and without excipients. Here we describe the results of all clinical trials evaluating PEA’s efficacy and safety in nerve compression syndromes: sciatic pain and pain due to carpal tunnel syndrome, and review preclinical evidence in nerve impingement models. Both the pharmacological studies as well as the clinical trials supported PEA’s action as an analgesic compound. In total, eight clinical trials have been published in such entrapment syndromes, and 1,366 patients have been included in these trials. PEA proved to be effective and safe in nerve compression syndromes. In one pivotal, double blind, placebo controlled trial in 636 sciatic pain patients, the number needed to treat to reach 50% pain reduction compared to baseline was 1.5 after 3 weeks of treatment. Furthermore, no drug interactions or troublesome side effects have been described so far. Physicians are not always aware of PEA as a relevant and safe alternative to opioids and co-analgesics in the treatment of neuropathic pain. Especially since the often prescribed co-analgesic pregabaline has been proven to be ineffective in sciatic pain in a double blind enrichment trial, PEA should be considered as a new and safe treatment option for nerve compression syndromes.

Evolution in pharmacologic thinking around the natural analgesic palmitoylethanolamide: from nonspecific resistance to PPAR-α agonist and effective nutraceutical

The history of development of new concepts in pharmacology is a highly interesting topic. This review discusses scientific insights related to palmitoylethanolamide (PEA) and its progression over a period of six decades, especially in light of the work of the science sociologists, Ludwig Fleck and Thomas Kuhn. The discovery of the cannabis receptors and the nuclear peroxisome proliferator-activated receptors was the beginning of a completely new understanding of many important homeostatic physiologic mechanisms in the human body. These discoveries were necessary for us to understand the analgesic and anti-inflammatory activity of PEA, a body-own fatty amide. PEA is a nutrient known already for more than 50 years. PEA is synthesized and metabolized in animal cells via a number of enzymes and has a multitude of physiologic functions related to metabolic homeostasis. PEA was identified in the 1950s as a therapeutic principle with potent anti-inflammatory properties. Since 1975, its analgesic properties have been noted and explored in a variety of chronic pain states. Since 2008, PEA has been available as a nutraceutical under the brand names Normast® and PeaPure®. A literature search on PEA meanwhile has yielded over 350 papers, all referenced in PubMed, describing the physiologic properties of this endogenous modulator and its pharmacologic and therapeutic profile. This review describes the emergence of concepts related to the pharmacologic profile of PEA, with an emphasis on the search into its mechanism of action and the impact of failing to identify such mechanism in the period 1957–1993, on the acceptance of PEA as an anti-inflammatory and analgesic compound.

Treatment of chronic regional pain syndrome type 1 with palmitoylethanolamide and topical ketamine cream: modulation of nonneuronal cells

Chronic regional pain syndrome (CRPS) can be intractable to treat and patients sometimes suffer for many years. Therefore, new treatment strategies are needed to alleviate symptoms in CRPS patients. This case report describes a patient suffering from intractable CRPS type 1 for 13 years. Due to her swollen painful feet and left knee she is wheelchair-bound. The combination of palmitoylethanolamide and ketamine 10% cream reduced her pain by more than 50% after 1 month of treatment, and a marked reduction in swelling and skin discoloration was noticed. Furthermore, she could walk independently again and she experienced no side effects. Thus, palmitoylethanolamide and topical ketamine could be a combination therapy option for treating CRPS patients.

Therapeutic utility of palmitoylethanolamide in the treatment of neuropathic pain associated with various pathological conditions: a case series

Palmitoylethanolamide (PEA), an endogenous fatty acid amide, has been demonstrated to bind to a receptor in the cell nucleus - the peroxisome proliferator-activated receptor - and performs a great variety of biological functions related to chronic and neuropathic pain and inflammation, as has been demonstrated in clinical trials. These include peripheral neuropathies such as diabetic neuropathy, chemotherapy-induced peripheral neuropathy, carpal tunnel syndrome, sciatic pain, osteoarthritis, low-back pain, failed back surgery syndrome, dental pains, neuropathic pain in stroke and multiple sclerosis, chronic pelvic pain, postherpetic neuralgia, and vaginal pains. Probably due to the fact that PEA is an endogenous modulator as well as a compound in food, such as eggs and milk, no serious side effects have been reported, nor have drug-drug interactions. This article presents a case series describing the application and potential efficacy and safety of PEA in the treatment of various syndromes associated with chronic pain that is poorly responsive to standard therapies.

Multimodal stepped care approach with acupuncture and PPAR-α agonist palmitoylethanolamide in the treatment of a patient with multiple sclerosis and central neuropathic pain

Central neuropathic pain is a common debilitating symptom in patients with multiple sclerosis. Side effects of analgesics often limit reaching therapeutic dosages. In this case report, a 61-year-old woman with chronic central neuropathic pain due to multiple sclerosis is described. Acupuncture could only partly and temporarily reduce the pain. However, after adding the natural compound palmitoylethanolamide, a glial modulator and peroxisome proliferator-activated receptor-α agonist, pain reduction was more pronounced and the interval between acupuncture sessions could be increased. A multimodal stepped care approach is demonstrated, with acupuncture and palmitoylethanolamide both influencing non-neuronal cells, such as activated glial cells, which are key factors in the development and maintenance of neuropathic pain.

Enhancing Acupuncture by Low Dose Naltrexone

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.

Effectiveness of ipsapirone, a 5-HT-1A partial agonist, in major depressive disorder: support for the role of 5-HT-1A receptors in the mechanism of action of serotonergic antidepressants

Desensitisation of serotonin 1A (5-HT-1A) receptors is a leading hypothesis for the mechanism of action of antidepressants which block serotonin reuptake. This hypothesis predicts that direct-acting 5-HT-1A agonists should also exhibit anti-depressant properties. Here we report the results of the first large-scale controlled study of the efficacy and tolerability of a 5-HT-1A agonist in outpatients with major depressive disorder (MDD). Three hundred and seventy-three subjects meeting DSM-III-R criteria for MDD participated in this randomised, double-blind comparison of the 5-HT-1A partial agonist ipsapirone (5 mg, 7.5 mg and 10 mg t.i.d.) to placebo t.i.d. Improvement in depressive symptoms relative to placebo, as measured by the Hamilton Depression Rating Scale, occurred in the ipsapirone (7.5 mg t.i.d.) group with a magnitude of effect (D=-2.53 points) that was statistically significant (p=0.010). Adverse events occurred in 76% of the placebo patients and 92% of the ipsapirone patients. A dose-related increase in the incidence of adverse events led to discontinuation of treatment with the 10 mg t.i.d. Results of this study demonstrate that ipsapirone, at a dose of 7.5 mg t.i.d., is an effective antidepressant agent in the treatment of MDD, supporting the hypothesised role of 5-HT-1A receptors in the mechanism of action of serotonin reuptake inhibitors. However, as a potential therapeutic agent for depression, ipsapirone shows only a modest magnitude of drug-placebo differences as well as a side-effect profile less favorable than many of the newer antidepressants.