Evidence-based data from animal and human experimental studies on pain relief with antidepressants: a structured review

Fibromyalgia Animal Models Using Intermittent Cold and Psychological Stress

Fibromyalgia (FM) is a chronic pain condition characterized by widespread musculoskeletal pain and other frequent symptoms such as fatigue, sleep disturbance, cognitive impairment, and mood disorder. Based on the view that intermittent stress would be the most probable etiology for FM, intermittent cold- and intermittent psychological stress-induced generalized pain (ICGP and IPGP) models in mice have been developed and validated as FM-like pain models in terms of the patho-physiological and pharmacotherapeutic features that are shared with clinical versions. Both models show long-lasting and generalized pain and female-predominant sex differences after gonadectomy. Like many other neuropathic pain models, ICGP and IPGP were abolished in lysophosphatidic acid receptor 1 (LPAR1) knock-out mice or by LPAR1 antagonist treatments, although deciding the clinical importance of this mechanism depends on waiting for the development of a clinically available LPAR1 antagonist. On the other hand, the nonsteroidal anti-inflammatory drug diclofenac with morphine did not suppress hyperalgesia in these models, and this is consistent with the clinical findings. Pharmacological studies suggest that the lack of morphine analgesia is associated with opioid tolerance upon the stress-induced release of endorphins and subsequent counterbalance through anti-opioid NMDA receptor mechanisms. Regarding pharmacotherapy, hyperalgesia in both models was suppressed by pregabalin and duloxetine, which have been approved for FM treatment in clinic. Notably, repeated treatments with mirtazapine, an α2 adrenergic receptor antagonist-type antidepressant, and donepezil, a drug for treating Alzheimer's disease, showed potent therapeutic actions in these models. However, the pharmacotherapeutic treatment should be carried out 3 months after stress, which is stated in the FM guideline, and many preclinical studies, such as those analyzing molecular and cellular mechanisms, as well as additional evidence using different animal models, are required. Thus, the ICGP and IPGP models have the potential to help discover and characterize new therapeutic medicines that might be used for the radical treatment of FM, although there are several limitations to be overcome.

Early-life exposure to selective serotonin reuptake inhibitors: Long-term effects on pain and affective comorbidities

A growing body of evidence indicates that early‐life exposure to selective serotonin reuptake inhibitor has long‐term consequences on the offspring's pain in addition to affective disorders like anxiety disorder and major depression. Serotonin, besides its role in regulating pain and emotions, promotes neuronal network formation. The prefrontal cortex and the amygdala are two key brain regions involved in the modulation of pain and its affective comorbidities. Thus, the aim of this review is to understand how early‐life selective serotonin reuptake inhibitor exposure alters the developing prefrontal cortex and amygdala and thereby underlies the long‐term changes in pain and its affective comorbidities in later life. While there is still limited data on the effects of early‐life selective serotonin reuptake inhibitor exposure on pain, there is a substantial body of evidence on its affective comorbidities. From this perspective paper, four conclusions emerged. First, early‐life selective serotonin reuptake inhibitor exposure results in long‐term nociceptive effects, which needs to be consistently studied to clarify. Second, it results in enhanced depressive‐like behaviour and diminished exploratory behaviour in adult rodents. Third, early‐life selective serotonin reuptake inhibitor exposure alters serotonergic levels, transcription factors expression, and brain‐derived neurotrophic factor levels, resulting in hyperconnectivity within the amygdala and the prefrontal cortex. Finally, it affects antinociceptive inputs of the prefrontal cortex and the amygdala in the spinal cord. We conclude that early‐life selective serotonin reuptake inhibitor exposure affects the maturation of prefrontal cortex and amygdala circuits and thereby enhances their antinociceptive inputs in the spinal cord.

The Clinical Difference between Gabapentin and Pregabalin: Data from a Pilot Comparative Trial

BACKGROUND

Similar anticonvulsants, such as gabapentin and pregabalin are recommended in neuropathic pain management, however little is known about their clinical differences in cases of low back pain. This paper aims to highlight some of the possible clinical differences between gabapentin and pregabalin in low back pain.

METHODS

Patients with moderate to severe low back pain were recruited. Eligible patients were randomised to receive either pregabalin (300 mg/day)or gabapentin (800 mg/day) for six weeks. The primary outcome measure was pain intensity according to the Visual Analogue Score (VAS) at baseline and at six weeks. The secondary outcome measures were: anxiety, insomnia, fatigue and the self-rated (GCI), measured at baseline, second, fourth, and the sixth week.

RESULTS

A total of 64 patients, pregabalin group (n=28), gabapentin group (n=36) completed the study. While pregabalin group showed a significantly lower pain score (p=0.039). The gabapentin group showed significant improvement in anxiety (p=0.001), insomnia (p=0.001), general fatigue (p=0.009), physical fatigue (p=0.001), reduce activity (p=0.001), and mental fatigue (p=0.014) higher than that of pregabalin. No difference in (GCI) was seen at six weeks.

CONCLUSION

This is the first trial aimed at comparing gabapentin with pregabalin in NLBP. Although the results are preliminary, in our pilot study pregabalin was found to be superior in pain reduction, gabapentin demonstrated better effect on anxiety, insomnia and fatigue symptoms. The results are preliminary and studies with a larger sample size are still required.

The Effects of Posttraumatic Stress and Trauma-Focused Disclosure on Experimental Pain Sensitivity Among Trauma-Exposed Women

Previous studies evaluating the impact of trauma history and posttraumatic stress disorder (PTSD) on pain sensitivity have yielded inconsistent findings. The presence of trauma-related negative affective states may account for these discrepancies. The current study aimed to evaluate the effect of PTSD and trauma-related negative affect on sensory, affective, physiological, and neuroendocrine responses to an experimental pain task. Trauma-exposed adult women (N = 87) with or without probable PTSD underwent an emotional disclosure paradigm during which they wrote about a traumatic event or a neutral topic. Participants then completed a pain induction procedure. Sensory and affective reports of pain, as well as physiological and neuroendocrine reactivity, were assessed. Compared to women without PTSD, those with PTSD demonstrated decreased sensory pain responses, η_p ² = .11, including increased time to pain detection (i.e., threshold) and ability to withstand the pain stimuli (i.e., tolerance) after accounting for relevant covariates. Women with PTSD also demonstrated increased cortisol reactivity following the pain stimulus, η_p ² = .06. The main and interactive effects of PTSD group and writing condition did not significantly predict alterations in affective reports of pain or heart rate reactivity. The results suggest that PTSD symptoms may contribute to alterations in pain sensitivity in trauma-exposed women, but this association is complex and requires further exploration.

Targeting tumor necrosis factor in the brain relieves neuropathic pain

Neuropathic pain is a chronic syndrome caused by direct damage to or disease of the somatosensory nervous system. The lack of safe, adequate and sustained pain relief offered by present analgesic treatments is most alarming. While many treatment options are available to manage chronic pain, such as antidepressants, non-steroidal anti-inflammatory agents, opioids, and anticonvulsants, chronic neuropathic pain remains largely unmanaged. Compounding the dilemma of ineffective chronic pain treatments is the need to provide relief from suffering and yet not contribute to the scourge of drug abuse. A recent epidemic of addiction and accidental drug prescription overdoses parallel the increased use of opioid treatment, even though opioids are rarely an effective treatment of relieving chronic pain. To make matters worse, opioids may contribute to exacerbating pain, and side-effects such as cognitive impairment, nausea, constipation, development of tolerance, as well as their potential for addiction and overdose deaths exist. Clearly, there is an urgent need for alternative, non-opiate treatment of chronic pain. Innovative discoveries of pertinent brain mechanisms and functions are key to developing effective, safe treatments. Pioneering work has revealed the essential effects of the pleiotropic mediator tumor necrosis factor (TNF) on brain functioning. These studies establish that TNF inhibits norepinephrine release from hippocampal neurons, and show that excess TNF production within the hippocampus occurs during neuropathic pain, which mobilizes additional mechanisms that further inhibit norepinephrine release. Significantly, it has been verified that elevated levels of TNF in the brain are actually required for neuropathic pain development. Since TNF decreases norepinephrine release in the brain, enhanced TNF levels would prevent engagement of the norepinephrine descending inhibitory neuronal pain pathways. Increased levels of TNF in the brain are therefore critical to the development of neuropathic pain. Therefore, strategies that decrease this enhanced TNF expression in the brain will have superior analgesic efficacy. We propose this novel approach of targeting the pathologically high levels of brain TNF as an effective strategy in the treatment of the devastating syndrome of chronic pain.

Multi-biomarker investigation to assess toxicity induced by two antidepressants on Dreissena polymorpha

Antidepressants are one of the main pharmaceutical classes detected in the aquatic environment. Nevertheless, there is a dearth of information regarding their potential adverse effects on non-target organisms. Thus, the aim of this study was the evaluation of sub-lethal effects on the freshwater mussel Dreissena polymorpha of two antidepressants commonly found in the aquatic environment, namely Fluoxetine (FLX) and Citalopram (CT). D. polymorpha specimens were exposed to FLX and CT alone and to their mixture (MIX) at the environmental concentration of 500ng/L for 14days. We evaluated the sub-lethal effects in the mussel soft tissues by means of a biomarker suite: the activity of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) and the activity of the phase II detoxifying enzyme glutathione-S-transferase (GST). The oxidative damage was evaluated by lipid peroxidation (LPO) and protein carbonylation (PCC), while genetic damage was tested on D. polymorpha hemocytes by Single Cell Gel Electrophoresis (SCGE) assay, DNA diffusion assay and micronucleus test (MN test). Finally, the functionality of the ABC transporter P-glycoprotein (P-gp) was measured in D. polymorpha gills. Our results highlight that CT, MIX and to a lesser extent FLX, caused a significant alteration of the oxidative status of bivalves, accompanied by a significant reduction of P-gp efflux activity. However, only FLX induced a slight, but significant, increase in apoptotic and necrotic cell frequencies. Considering the variability in biomarker response and to perform a toxicity comparison of tested molecules, we integrated each endpoint into the Biomarker Response Index (BRI). The data integration showed that 500ng/L of FLX, CT and their MIX have the same toxicity on bivalves.

Central Sensitization and Neuropathic Features of Ongoing Pain in a Rat Model of Advanced Osteoarthritis

Osteoarthritis (OA) pain is most commonly characterized by movement-triggered joint pain. However, in advanced disease, OA pain becomes persistent, ongoing and resistant to treatment with nonsteroidal anti-inflammatory drugs (NSAIDs). The mechanisms underlying ongoing pain in advanced OA are poorly understood. We recently showed that intra-articular (i.a.) injection of monosodium iodoacetate (MIA) into the rat knee joint produces concentration-dependent outcomes. Thus, a low dose of i.a. MIA produces NSAID-sensitive weight asymmetry without evidence of ongoing pain and a high i.a. MIA dose produces weight asymmetry and NSAID-resistant ongoing pain. In the present study, palpation of the ipsilateral hind limb of rats treated 14 days previously with high, but not low, doses of i.a. MIA produced expression of the early oncogene, FOS, in the spinal dorsal horn. Inactivation of descending pain facilitatory pathways using a microinjection of lidocaine within the rostral ventromedial medulla induced conditioned place preference selectively in rats treated with the high dose of MIA. Conditioned place preference to intra-articular lidocaine was blocked by pretreatment with duloxetine (30 mg/kg, intraperitoneally at -30 minutes). These observations are consistent with the likelihood of a neuropathic component of OA that elicits ongoing, NSAID-resistant pain and central sensitization that is mediated, in part, by descending modulatory mechanisms. This model provides a basis for exploration of underlying mechanisms promoting neuropathic components of OA pain and for the identification of mechanisms that might guide drug discovery for treatment of advanced OA pain without the need for joint replacement.

PERSPECTIVE

Difficulty in managing advanced OA pain often results in joint replacement therapy in these patients. Improved understanding of mechanisms driving NSAID-resistant ongoing OA pain might facilitate development of alternatives to joint replacement therapy. Our findings suggest that central sensitization and neuropathic features contribute to NSAID-resistant ongoing OA joint pain.

Pharmacologic basis for the use of selective norepinephrine reuptake inhibitors for the treatment of neuropathic pain conditions

Introduction

This article will review the pharmacologic and clinical evidence supporting the use of selective norepinephrine reuptake inhibitors, most notably atomoxetine, for the treatment of neuropathic pain states. Many medications initially marketed for psychiatric indications have gained widespread use for their analgesic properties after additional research.

Methods

In search of alternative treatments for neuropathic pain, current guidelines, published reviews, and primary literature, including both rodent and human trials, were reviewed.

Results and Discussion

The first group of medications to gain widespread use in pain management was the tricyclic antidepressants. As further research was completed and serotonin norepinephrine reuptake inhibitors began to be utilized for their analgesic properties, a growing body of evidence began to indicate that the analgesic properties of these medications were primarily due to the blockade of norepinephrine reuptake with serotonin playing only a minimal role.

Pharmacogenetics and analgesic effects of antidepressants in chronic pain management

Antidepressants are widely administered to chronic pain patients, but there is large interindividual variability in their efficacy and adverse effect rates that may be attributed to genetic factors. Studies have attempted to determine the impact of genetic polymorphisms in enzymes and transporters that are involved in antidepressant pharmacokinetics, for example, cytochrome P450 and P-gp. The impacts of genetic polymorphisms in the targets of antidepressants, such as the serotonin receptor or transporter, the noradrenaline transporter and the COMT and monoamine oxydase enzymes, have also been described. This manuscript discusses the current knowledge of the influence of genetic factors on the plasma concentrations, efficacy and adverse effects of the major antidepressants used in pain management.

Preclinical to clinical translation of CNS transporter occupancy of TD-9855, a novel norepinephrine and serotonin reuptake inhibitor

BACKGROUND

Monoamine reuptake inhibitors exhibit unique clinical profiles that reflect distinct engagement of the central nervous system (CNS) transporters.

METHODS

We used a translational strategy, including rodent pharmacokinetic/pharmacodynamic modeling and positron emission tomography (PET) imaging in humans, to establish the transporter profile of TD-9855, a novel norepinephrine and serotonin reuptake inhibitor.

RESULTS

TD-9855 was a potent inhibitor of norepinephrine (NE) and serotonin 5-HT uptake in vitro with an inhibitory selectivity of 4- to 10-fold for NE at human and rat transporters. TD-9855 engaged norepinephrine transporters (NET) and serotonin transporters (SERT) in rat spinal cord, with a plasma EC50 of 11.7 ng/mL and 50.8 ng/mL, respectively, consistent with modest selectivity for NET in vivo. Accounting for species differences in protein binding, the projected human NET and SERT plasma EC50 values were 5.5 ng/mL and 23.9 ng/mL, respectively. A single-dose, open-label PET study (4-20mg TD-9855, oral) was conducted in eight healthy males using the radiotracers [(11)C]-3-amino-4- [2-[(di(methyl)amino)methyl]phenyl]sulfanylbenzonitrile for SERT and [(11)C]-(S,S)-methylreboxetine for NET. The long pharmacokinetic half-life (30-40 h) of TD-9855 allowed for sequential assessment of SERT and NET occupancy in the same subject. The plasma EC50 for NET was estimated to be 1.21 ng/mL, and at doses of greater than 4 mg the projected steady-state NET occupancy is high (>75%). After a single oral dose of 20mg, SERT occupancy was 25 (±8)% at a plasma level of 6.35 ng/mL.

CONCLUSIONS

These data establish the CNS penetration and transporter profile of TD-9855 and inform the selection of potential doses for future clinical evaluation.

Does pain interfere with antidepressant depression treatment response and remission in patients with depression and pain? An evidence-based structured review

OBJECTIVE

The objective of this evidence-based structured review was to determine if there is consistent evidence that pain interferes with achieving antidepressant treatment response/remission of depression in patients with depression and pain.

METHODS

After exclusion criteria were applied, of 2,801 studies/reports, 17 studies addressed this question. They were sorted into the four hypotheses outlined herein after. The percentage of studies supporting/not supporting each hypothesis was calculated. The strength and consistency of the evidence for each hypothesis were rated according to the Agency for Health Care Research and Quality (AHRQ) guidelines.

RESULTS

For the first hypothesis (pretreatment pain levels will predict antidepressant depression response), nine out of 10 (90%) studies supported it. For the second hypothesis (treatment decreases in pain will be associated with antidepressant depression response), two out of two (100%) studies supported it. For the third hypothesis (pretreatment pain levels will predict antidepressant depression remission), six out of six (100%) studies supported it. For the fourth hypothesis (treatment decreases in pain will be associated with antidepressant depression remission), five out of five (100%) supported it. Utilizing these percentages and AHRQ guidelines, hypotheses 1, 3, and 4 received an A rating for consistency of studies in supporting them. A consistency rating for hypothesis 2 could not be generated because of too few studies in that group.

CONCLUSIONS

Consistent evidence was found that antidepressant treatment of depression in patients with depression and pain can be negatively impacted by pain for achieving depression response/remission. However, the overall number of studies supporting each hypothesis was small. In addition, several potential confounders of the results of this study were identified.

Uliginosin B, a natural phloroglucinol derivative, presents a multimediated antinociceptive effect in mice

Objective

Investigate the involvement of monoaminergic and glutamatergic systems on the antinociceptive and ataxic effects of uliginosin B, which we have already demonstrated to be a promising molecular scaffold to develop new analgesic drugs.

Methods

Uliginosin B was obtained from hexane extract of aerial parts of Hypericum polyanthemum by chromatographic methods. Uliginosin B antinociceptive and motor coordination effects were evaluated in mice by using hot-plate (15 and 90 mg/kg, i.p.) and rotarod (90 mg/kg, i.p.) tests, respectively. The mechanism of action was investigated through pretreatments with prazosin 1 mg/kg intraperitoneal (α1 receptor antagonist), yohimbine 5 mg/kg intraperitoneal (α2 receptor antagonist), pCPA 300 mg/kg intraperitoneal (serotonin synthesis inhibitor) and MK-801 0.25 mg/kg intraperitoneal (N-methyl-D-aspartic acid receptor antagonist).

Key findings

The antinociceptive effect of uliginosin B (15 and 90 mg/kg, i.p.) was reduced significantly by pCPA and MK-801. Prazosin and yohimbine improved the antinociceptive effect of the highest dose (90 mg/kg, i.p.) of uliginosin B only. The ataxic effect of uliginosin B (90 mg/kg, i.p.) was completely prevented by pretreatment with pCPA or MK-801, but it was unaffected by pretreatment with prazosin or yohimbine.

Conclusion

These data confirm the contribution of monoaminergic neurotransmission as well as provide the first evidence of glutamatergic neurotransmission contribution to the uliginosin B effects.

Antinociceptive Effects of the Serotonin and Noradrenaline Reuptake Inhibitors Milnacipran and Duloxetine on Vincristine-Induced Neuropathic Pain Model in Mice

Vincristine is an anticancer drug used to treat a variety of cancer types, but it frequently causes peripheral neuropathy. Neuropathic pain is often associated with the appearance of abnormal sensory signs, such as allodynia. Milnacipran and duloxetine, serotonin/noradrenaline reuptake inhibitors, have shown efficacy against several chronic pain syndromes. In this study, we investigated the attenuation of vincristine-induced mechanical allodynia in mice by milnacipran and duloxetine. To induce peripheral neuropathy, vincristine was administered once per day (0.1 mg/kg, intraperitoneally (i.p.)) for 7 days. Mechanical allodynia was evaluated by measuring the withdrawal response to stimulation with a von Frey filament. In vincristine-treated mice, mechanical allodynia was observed on days 3-28 of vincristine administration. A single administration of milnacipran (40 mg/kg, i.p.) or duloxetine (20 mg/kg, i.p.) had no effect on vincristine-induced mechanical allodynia. However, repeated administration of milnacipran (20 or 40 mg/kg, once per day, i.p.) or duloxetine (5, 10, or 20 mg/kg, once per day, i.p.) for 7 days significantly reduced vincristine-induced mechanical allodynia. These results suggest that chronic vincristine administration induces mechanical allodynia, and that repeated milnacipran and duloxetine administration may be an effective approach for the treatment of neuropathic pain caused by vincristine treatment for cancer.

Disruption of 5-HT2A receptor-PDZ protein interactions alleviates mechanical hypersensitivity in carrageenan-induced inflammation in rats

Despite common pathophysiological mechanisms, inflammatory and neuropathic pain do not respond equally to the analgesic effect of antidepressants, except for selective serotonin reuptake inhibitors (SSRIs), which show a limited efficacy in both conditions. We previously demonstrated that an interfering peptide (TAT-2ASCV) disrupting the interaction between 5-HT2A receptors and its associated PDZ proteins (e.g. PSD-95) reveals a 5-HT2A receptor-mediated anti-hyperalgesic effect and enhances the efficacy of fluoxetine (a SSRI) in diabetic neuropathic pain conditions in rats. Here, we have examined whether the same strategy would be useful to treat inflammatory pain. Sub-chronic inflammatory pain was induced by injecting λ-carrageenan (100 µl, 2%) into the left hind paw of the rat. Mechanical hyperalgesia was assessed after acute treatment with TAT-2ASCV or/and fluoxetine (SSRI) 2.5 h after λ-carrageenan injection. Possible changes in the level of 5-HT2A receptors and its associated PDZ protein PSD-95 upon inflammation induction were quantified by Western blotting in dorsal horn spinal cord. Administration of TAT-2ASCV peptide (100 ng/rat, intrathecally) but not fluoxetine (10 mg/kg, intraperitoneally) relieves mechanical hyperalgesia (paw pressure test) in inflamed rats. This anti-hyperalgesic effect involves spinal 5-HT2A receptors and GABAergic interneurons as it is abolished by a 5-HT2A antagonist (M100907, 150 ng/rat, intrathecally) and a GABAA antagonist, (bicuculline, 3 µg/rat, intrathecally). We also found a decreased expression of 5-HT2A receptors in the dorsal spinal cord of inflamed animals which could not be rescued by TAT-2ASCV injection, while the amount of PSD-95 was not affected by inflammatory pain. Finally, the coadministration of fluoxetine does not further enhance the anti-hyperalgesic effect of TAT-2ASCV peptide. This study reveals a role of the interactions between 5-HT2A receptors and PDZ proteins in the pathophysiological pathways of inflammatory pain and opens new perspectives in its control thanks to molecules disrupting 5-HT2A receptor/PDZ protein interactions.

Safety and efficacy of esreboxetine in patients with fibromyalgia: a fourteen-week, randomized, double-blind, placebo-controlled, multicenter clinical trial

OBJECTIVE

To evaluate the efficacy, tolerability, and safety of multiple fixed dosages of esreboxetine for the treatment of fibromyalgia.

METHODS

Patients meeting the American College of Rheumatology criteria for fibromyalgia were randomized to receive esreboxetine at dosages of 4 mg/day (n=277), 8 mg/day (n=284), or 10 mg/day (n=283) or matching placebo (n=278) for 14 weeks. The primary efficacy outcomes were the weekly mean pain score and the Fibromyalgia Impact Questionnaire (FIQ) total score at week 14. Secondary efficacy measures included scores for the Patient's Global Impression of Change (PGIC) scale, the Global Fatigue Index (GFI), and the 36-item Short-Form health survey (SF-36; physical function scale only) at week 14. The safety profile of esreboxetine was evaluated based on adverse events and other safety measures.

RESULTS

Patients receiving all dosages of esreboxetine demonstrated statistically significant improvements in the pain score (P≤0.025), the FIQ score (P≤0.023), and the PGIC score (P≤0.007) compared with patients in the placebo group. Additionally, patients receiving esreboxetine at dosages of 4 mg/day and 8 mg/day showed statistically significant improvements in the GFI score compared with those receiving placebo (P=0.001). No significant differences in SF-36 physical function scores were observed between patients receiving esreboxetine (any dosage) and those receiving placebo. Adverse events were mostly mild to moderate in severity; insomnia, constipation, dry mouth, nausea, dizziness, hot flush, headache, hyperhidrosis, and palpitations were reported most frequently.

CONCLUSION

Esreboxetine was generally well tolerated and was associated with significant improvements in pain, FIQ, PGIC, and fatigue scores compared with placebo. The lack of a dose-response relationship in both the efficacy and safety analyses suggests that esreboxetine at a dosage of 4 mg/day would offer clinical benefit with the least risk of drug exposure.

The association between non-medical prescription drug use, depressive symptoms, and suicidality among college students

PURPOSE

Studies have substantiated a relationship between drug use, depression, and suicidality. However, little research has examined this relationship with prescription drugs. Given the prevalence of non-medical prescription drug use (NMPDU) among college students, this study explored the association between general and specific NMPDU, depressive symptoms, and suicidality.

METHODS

Data from the Fall 2008 National College Health Assessment (NCHA) was utilized (N=22,783). Five separate logistic regression models were employed, with the first combining any NMPDU (antidepressants, painkillers, sedatives, and stimulants) followed by four additional regressions for each drug, and then separated by gender. Models were estimated before and after control for key covariates.

RESULTS

Approximately 13% of participants reported NMPDU. After covariate adjustment, those who reported feeling hopeless, sad, depressed, or considered suicide were 1.22-1.31 times more likely to report NMPDU (p<.05). Those who reported feeling hopeless, sad, or depressed were 1.18-1.43 times more likely to report opioid painkiller use; those who reported feeling sad, depressed, or considered suicide were 1.22-1.38 times more likely to report stimulant use; those who reported being depressed were 1.36 times more likely to report sedative use; and those who reported feeling hopeless or depressed were 1.44 and 1.91 times more likely to report antidepressant use (p<.05). When the adjusted models were repeated separately by gender, results were more pronounced for females, especially for females who reported painkiller use.

CONCLUSIONS

Depressive symptoms and suicidality were significantly associated with greater odds of any NMPDU, with painkiller use (especially for females) representing the greatest correlate among college students. Results suggest that students may be inappropriately self-medicating psychological distress with prescription medications.

Population analyses of efficacy and safety of ABT-594 in subjects with diabetic peripheral neuropathic pain

ABT-594, a neuronal nicotinic acetylcholine receptor ligand, is 30- to 100-fold more potent than morphine in animal models of nociceptive and neuropathic pain. Efficacy and safety of ABT-594 in subjects with painful diabetic polyneuropathy was evaluated in a phase 2 study. The objective of this work was to use a nonlinear mixed effects model-based approach for characterizing the relationship between dose and response (efficacy and safety) of ABT-594. Subjects (N = 266) were randomized into four groups in a double-blind, placebo-controlled, 7-week study to receive twice daily regimens of placebo or 150, 225, and 300 μg of ABT-594. The primary efficacy variable, pain score (11-point Likert scale), was assessed on five occasions. The probability of change from baseline pain score of ≥1, ≥2, and ≥3 was modeled using cumulative logistic regression with dose and days of treatment as explanatory variables. The incidence of five most frequently occurring adverse events (AEs) was modeled using linear logistic regression. ABT-594 ED(50) values (improvement in 50% of subjects) for improvement in pain scores of ≥1, ≥2, and ≥3 were 50, 215, and 340 μg, respectively, for the average number of days (33) on treatment. The rank order of ED(50) values for AEs was nausea, vomiting, dizziness, headache, and abnormal dreams; nicotine users were less sensitive to AEs. Population pharmacodynamic models developed to characterize the improvement in pain score and incidence of adverse events indicate an approximately twofold separation between the ED(50) values for efficacy and AEs.

The antinociceptive effects of intravenous tianeptine in colorectal distension-induced visceral pain in rats: the role of 5-HT₃ receptors

Tianeptine is an unusual tricyclic antidepressant drug. In this study, we aimed to investigate the antinociceptive effect of tianeptine on visceral pain in rats and to determine whether possible antinociceptive effect of tianeptine is mediated by serotonergic (5-HT(2,3)) and noradrenergic (α(1,2)) receptor subtypes. Male Sprague Dawley rats (250-300 g) were supplied with a venous catheter, for drug administrations, and enameled nichrome electrodes, for electromyography, at external oblique musculature. Colorectal distension (CRD) was employed as the noxious visceral stimulus and the visceromotor response (VMR) to CRD was quantified electromyographically before and 5, 15, 30, 60, 90 and 120 min after tianeptine administration. Antagonists were administered 10 min before tianeptine for their ability to change tianeptine antinociception. Intravenous administration of tianeptine (2.5-20 mg/kg) produced a dose-dependent reduction in VMR. Administration of 5-HT(3) receptor antagonist ondansetron (0.5, 1 and 2 mg/kg), but not 5-HT(2) receptor antagonist ketanserine (0.5, 1 and 2 mg/kg), reduced the antinociceptive effect of tianeptine (10mg/kg). In addition, administration of α(1)-adrenoceptor antagonist prazosin (1 mg/kg) or α(2)-adrenoceptor antagonist yohimbine (1 mg/kg) did not cause any significant effect on the tianeptine-induced antinociception. Our data indicate that intravenous tianeptine exerts a pronounced antinociception against CRD-induced visceral pain in rats, and suggests that the antinociceptive effect of tianeptine appears to be mediated in part by 5-HT(3) receptors, but does not involve 5-HT(2) receptors or α-adrenoceptors.

Sertraline inhibits formalin-induced nociception and cardiovascular responses

The objective of the present study was to determine the antihyperalgesic effect of sertraline, measured indirectly by the changes of sciatic afferent nerve activity, and its effects on cardiorespiratory parameters, using the model of formalin-induced inflammatory nociception in anesthetized rats. Serum serotonin (5-HT) levels were measured in order to test their correlation with the analgesic effect. Male Wistar rats (250-300 g) were divided into 4 groups (N = 8/per group): sertraline-treated group (Sert + Saline (Sal) and Sert + Formalin (Form); 3 mg·kg-1·day-1, ip, for 7 days) and saline-treated group (Sal + Sal and Sal + Form). The rats were injected with 5% (50 µL) formalin or saline into the right hind paw. Sciatic nerve activity was recorded using a silver electrode connected to a NeuroLog apparatus, and cardiopulmonary parameters (mean arterial pressure, heart rate and respiratory frequency), assessed after arterial cannulation and tracheotomy, were monitored using a Data Acquisition System. Blood samples were collected from the animals and serum 5-HT levels were determined by ELISA. Formalin injection induced the following changes: sciatic afferent nerve activity (+50.8 ± 14.7%), mean arterial pressure (+1.4 ± 3 mmHg), heart rate (+13 ± 6.8 bpm), respiratory frequency (+4.6 ± 5 cpm) and serum 5-HT increased to 1162 ± 124.6 ng/mL. Treatment with sertraline significantly reduced all these parameters (respectively: +19.8 ± 6.9%, -3.3 ± 2 mmHg, -13.1 ± 10.8 bpm, -9.8 ± 5.7 cpm) and serum 5-HT level dropped to 634 ± 69 ng/mL (P < 0.05). These results suggest that sertraline plays an analgesic role in formalin-induced nociception probably through a serotonergic mechanism.

Duloxetine in the acute and continuation treatment of major depressive disorder

Duloxetine is a serotonin-noradrenaline reuptake inhibitor with indications for use in the short term, continuation and maintenance treatment of major depression. Although clinicians currently have access to a range of medications for the treatment of depression, a significant number of patients fail to respond or remit from their illness despite adequate trials of treatment with multiple agents. A developing concept is that antidepressant strategies that combine multiple mechanisms of action may have advantages over agents with single mechanisms (i.e., selective serotonin reuptake inhibitors). As a dual-acting agent, duloxetine offers the promise of advantages in terms of efficacy over selective serotonin reuptake inhibitors while retaining a favorable safety and tolerability profile in comparison to older agents. Likewise, duloxetine is of interest in the treatment of certain conditions commonly seen in conjunction with major depression, particularly anxiety and pain, both of which may respond more favorably to agents that act on both serotonin and noradrenaline neurotransmitter systems.

Permanent relief from intermittent cold stress-induced fibromyalgia-like abnormal pain by repeated intrathecal administration of antidepressants

BACKGROUND

Fibromyalgia (FM) is characterized by chronic widespread pain, which is often refractory to conventional painkillers. Numerous clinical studies have demonstrated that antidepressants are effective in treating FM pain. We previously established a mouse model of FM-like pain, induced by intermittent cold stress (ICS).

RESULTS

In this study, we find that ICS exposure causes a transient increase in plasma corticosterone concentration, but not in anxiety or depression-like behaviors. A single intrathecal injection of an antidepressant, such as milnacipran, amitriptyline, mianserin or paroxetine, had an acute analgesic effect on ICS-induced thermal hyperalgesia at post-stress day 1 in a dose-dependent manner. In addition, repeated daily antidepressant treatments during post-stress days 1-5 gradually reversed the reduction in thermal pain threshold, and this recovery was maintained for at least 7 days after the final treatment. In addition, relief from mechanical allodynia, induced by ICS exposure, was also observed at day 9 after the cessation of antidepressant treatment. In contrast, the intravenous administration of these antidepressants at conventional doses failed to provide relief.

CONCLUSIONS

These results suggest that the repetitive intrathecal administration of antidepressants permanently cures ICS-induced FM pain in mice.

Pharmacotherapy for fibromyalgia

Fibromyalgia (FM) is a chronic disorder characterized by multifocal pain and other associated somatic symptoms including fatigue, insomnia, cognitive/memory problems, and even psychological distress. It appears that 2–4% of the general population suffers from FM. FM negatively impacts the physical functioning of its patients, as evidenced by difficulties with multiple daily activities, as well as affecting emotional health, social functioning, and health related quality of life. This review will discuss the potential theories that possibly contribute to the pathogenesis of FM, although the precise mechanism is unknown. The evolution of the assessment of FM will also be examined, with the waning use of tender point examinations and the appearance of new simple, practical diagnostic criteria. Although non-pharmacologic therapeutic options (exercise, education, cognitive–behavioral therapy) have been shown to be extremely effective in FM, the focus of this article will be on pharmacologic strategies. Non-Food and Drug Administration (FDA) approved as well as FDA approved agents will be presented. Each agent's therapeutic “niche” in FM management will be discussed based on its pharmacologic profile, patient responsiveness, and tolerability. Finally a clinical algorithm will be presented for the step-wise management of pain and other associated symptoms of FM.

Safety and efficacy of esreboxetine in patients with fibromyalgia: An 8-week, multicenter, randomized, double-blind, placebo-controlled study

BACKGROUND

Esreboxetine is an investigational, highly selective norepinephrine reuptake inhibitor that has been reported to have antinociceptive effects in preclinical pain models.

OBJECTIVE

This study assessed the efficacy and safety profile of esreboxetine in the management of fibromyalgia.

METHODS

This was a multicenter, randomized, double-blind, placebo-controlled trial in patients aged ≥18 years who met American College of Rheumatology criteria for fibromyalgia. Eligible patients were required to have a score ≥40 mm on the 100-mm visual analog scale of the Short-Form McGill Pain Questionnaire at screening and randomization, and a mean score ≥4 on an 11-point pain rating scale (from 0 = no pain to 10 = worst possible pain) based on the weekly mean pain score in the week before randomization. After a 1-week baseline period and a 2-week, single-blind, placebo run-in period, patients were randomized to receive esreboxetine or placebo for 8 weeks, followed by a 1-week follow-up period. Esreboxetine dosing was started at 2 mg/d and was escalated by 2 mg/d every 2 weeks until attainment of a dose of 8 mg/d or the maximum tolerated dose. The primary efficacy outcome was the change from baseline to week 8 in weekly mean pain scores, as derived from patients' daily pain ratings on the 11-point scale. Additional primary efficacy outcomes included changes in the Fibromyalgia Impact Questionnaire (FIQ) total score and the Patient Global Impression of Change (PGIC). The safety profile was evaluated based on observed and spontaneously reported adverse events, laboratory tests, and other safety measures.

RESULTS

One hundred thirty-four patients were randomized to each study group, but 1 patient in the placebo group did not receive treatment. Thus, the study population consisted of 267 patients (89.5% female; 88.4% white; mean age, ∼50 years [range, 20-84 years]). Twenty-seven patients in each group discontinued the study. Adverse events were the most common reason for discontinuation in the esreboxetine group (11 patients), compared with 3 discontinuing due to adverse events in the placebo group. Patient default (withdrawal of consent and loss to follow-up) was the most common reason for discontinuation in the placebo group (13 patients), compared with 10 in the esreboxetine group. The esreboxetine group had significantly greater improvement in the weekly mean pain score compared with the placebo group (mean [SE] change from baseline: -1.55 [0.16] vs -0.99 [0.16], respectively; P = 0.006). A significantly greater percentage of patients in the esreboxetine group reported a ≥30% reduction in pain scores compared with the placebo group (37.6% [50/133] vs 22.6% [30/133]; P = 0.004). Esreboxetine was associated with significant improvement compared with placebo in the FIQ total score (mean change from baseline: -15.63 [1.56] vs -8.07 [1.54]; P < 0.001). On the PGIC, significantly more patients in the esreboxetine group than in the placebo group reported their condition much or very much improved (odds ratio = 2.42; 90% CI, 1.549-3.786; P < 0.001). Esreboxetine also was associated with significant improvements in secondary outcomes compared with placebo. These included fatigue, as reflected in scores on the Multidimensional Assessment of Fatigue (mean [SE] change from baseline: -6.39 [0.75] vs -2.82 [0.75], respectively; P < 0.001), and scores on measures of patient function and health-related quality of life, including the 36-item Short Form Health Survey (SF-36) Physical Component Summary (mean change from baseline: 4.36 [0.59] vs 1.86 [0.59]; P = 0.002), the SF-36 Mental Component Summary (mean change from baseline: 4.25 [0.83] vs 1.81 [0.83]; P = 0.019), and the Sheehan Disability Scale total score (mean change from baseline: -6.50 [0.64] vs -2.79 [0.61]; P < 0.001). Numerically more patients in the esreboxetine group than in the placebo group reported at least one adverse event (71.6% vs 57.1%), most commonly constipation (17.2% vs 5.3%), insomnia (15.7% vs 3.0%), dry mouth (15.7% vs 2.3%), and headache (10.4% vs 2.3%).

CONCLUSIONS

In this 8-week trial in patients with fibromyalgia, esreboxetine was associated with significant reductions in pain scores compared with placebo. It was also associated with improvements in outcomes relevant to fibromyalgia, including the PGIC, function, and fatigue. ClinicalTrials.gov identifier: NCT00357825.

Fentanyl-trazodone-paracetamol triple drug combination: multimodal analgesia in a mouse model of visceral pain

Multimodal or balanced analgesia is commonly used in the management of acute and chronic pain in humans, in order to achieve the best analgesic/safety profile. Here, by using a model of visceral acute tonic pain, the acetic acid-induced writhing test of mice, we show a synergistic interaction between fentanyl, trazodone and paracetamol on the inhibition of nociception. First of all, once assessed that all drugs induced dose-related antinociceptive effects, they were mixed in fixed ratio (1:1) combinations and a synergistic drug-drug interaction was obtained in all circumstances. Thereafter, we assayed the effects of the triple combination of fentanyl-trazodone-paracetamol and it was demonstrated that they displayed a potent synergistic interaction on the inhibition of acetic acid-mediated nociception. Interestingly, drug dosage reduction permitted to reduce the incidence of possible adverse effects, namely exploratory activity and motor coordination, thus it was demonstrated that it improved the benefit/risk profile of such treatment. Afterwards, we attempted to elucidate the mechanism of action of such interaction, by means of the non-selective opioid receptor antagonist naloxone. Interestingly, naloxone completely antagonized the antinociceptive effects of fentanyl, and it also partially reversed paracetamol and trazodone mediated analgesia. Furthermore, when naloxone was co-administered with the triple-drug treatment it blocked the previously observed enhanced antinociceptive effects of the combination. Thus, these results indicated that the endogenous opioid system played a main role in the present drug-drug interaction. Overall, the triple combination of fentanyl-trazodone-paracetamol induced a potent synergistic antinociceptive effect, which could be of interest for optimal multimodal clinical analgesia.

Monoaminergic Antidepressants in the Relief of Pain: Potential Therapeutic Utility of Triple Reuptake Inhibitors (TRIs)

Over 75% of depressed patients suffer from painful symptoms predicting a greater severity and a less favorable outcome of depression. Imaging, anatomical and functional studies have demonstrated the existence of common brain structures, neuronal pathways and neurotransmitters in depression and pain. In particular, the ascending serotonergic and noradrenergic pathways originating from the raphe nuclei and the locus coeruleus; respectively, send projections to the limbic system. Such pathways control many of the psychological functions that are disturbed in depression and in the perception of pain. On the other hand, the descending pathways, from monoaminergic nuclei to the spinal cord, are specifically implicated in the inhibition of nociception providing rationale for the use of serotonin (5-HT) and/or norepinephrine (NE) reuptake inhibitors (SSRIs, NRIs, SNRIs), in the relief of pain. Compelling evidence suggests that dopamine (DA) is also involved in the pathophysiology and treatment of depression. Indeed, recent insights have demonstrated a central role for DA in analgesia through an action at both the spinal and suprasinal levels including brain regions such as the periaqueductal grey (PAG), the thalamus, the basal ganglia and the limbic system. In this context, dopaminergic antidepressants (i.e., containing dopaminergic activity), such as bupropion, nomifensine and more recently triple reuptake inhibitors (TRIs), might represent new promising therapeutic tools in the treatment of painful symptoms with depression. Nevertheless, whether the addition of the dopaminergic component produces more robust effects than single- or dual-acting agents, has yet to be demonstrated. This article reviews the main pathways regulating pain transmission in relation with the monoaminergic systems. It then focuses on the current knowledge regarding the in vivo pharmacological properties and mechanism of action of monoaminergic antidepressants including SSRIs, NRIs, SNRIs and TRIs. Finally, a synthesis of the preclinical studies supporting the efficacy of these antidepressants in analgesia is also addressed in order to highlight the relative contribution of 5-HT, NE and DA to nociception.

A review of SSRIs and SNRIs in neuropathic pain

IMPORTANCE OF THE FIELD

Selective serotonin reuptake inhibitors (SSRIs) and serotonin noradrenaline reuptake inhibitors (SNRIs) are becoming increasingly used in the treatment of neuropathic pain and fibromyalgia. However, they are not without adverse effects and their efficacy has not been clear because of conflicting evidence.

AREAS COVERED IN THIS REVIEW

We have examined the current evidence on the efficacy of SSRIs and SNRIs in the treatment of neuropathic pain and fibromyalgia. Relevant randomized, placebo-controlled studies were identified through a MEDLINE search of English-language literature from January 1990 to December 2009.

WHAT THE READER WILL GAIN

The evidence for efficacy of SSRIs in the treatment neuropathic pain is moderate at best. However, SNRIs, venlafaxine and duloxetine have been shown to be effective in the treatment of painful diabetic neuropathy and polyneuropathy. With fibromyalgia, both SSRIs (fluoxetine and paroxetine) and SNRIs (duloxetine and milnacipran) have been shown to improve pain relief, function and quality of life.

TAKE HOME MESSAGE

SSRIs and SNRIs may be considered in the treatment of neuropathic pain if treatment with tricyclic antidepressants and anticonvulsants fails, or if there are contraindications to these drugs. There is also sufficient evidence to indicate that SNRIs are effective in the treatment of fibromyalgia and may be considered early in the treatment of fibromyalgia.

WAY-318068: a novel, potent and selective noradrenaline re-uptake inhibitor with activity in rodent models of pain and depression

BACKGROUND AND PURPOSE

Antidepressants, which raise the CNS concentrations of 5-HT and noradrenaline, are frequently used in the treatment of chronic pain; however, it is not known if increasing CNS noradrenaline levels alone is sufficient for efficacy, in part resulting from a lack of small molecules with sufficient selectivity.

EXPERIMENTAL APPROACH

In this report, we present the in vitro pharmacological and in vivo pharmacokinetic and pharmacological properties of the novel, orally available and CNS penetrant inhibitor of the noradrenaline transporter (NET), WAY-318068 (1-[(1S,2R)-1-(3,5-difluorophenyl)-2-hydroxy-3-(methylamino)propyl]-7-fluoro-3,3-dimethyl-1,3-dihydro-2H-indol-2-one).

KEY RESULTS

WAY-318068 is a potent and effective inhibitor of the NET with a K(i) of 8.7 nM in a binding assay, and an IC(50) of 6.8 nM in an assay of transporter function, without significant binding to the dopamine transporter. Furthermore, the compound has only weak activity at the 5-HT transporter, leading to a functional selectivity of greater than 2500-fold. It is orally bioavailable with substantial quantities of the compound found in the CNS after oral dosing. As measured by microdialysis in rats, the compound causes a robust and significant increase in cortical noradrenaline levels without affecting 5-HT. WAY-318068 was effective in models of acute, visceral, inflammatory, osteoarthritic, neuropathic, diabetic and bone cancer pain, as well as in traditional models of depression at doses that do not cause motor deficits.

CONCLUSIONS AND IMPLICATIONS

Collectively, the present results support the conclusion that selectively increasing CNS levels of noradrenaline is sufficient for efficacy in models of depression and pain.

The pathophysiology, diagnosis and treatment of fibromyalgia

Research in fibromyalgia has increased understanding of the possible genetic and environmental factors that could be involved in the etiology of fibromyalgia. There is now substantial evidence for augmentation of central pain processing in fibromyalgia. Because the clinical presentation of fibromyalgia is heterogeneous, treatment recommendations must be individualized for each patient. The rapid growth of trials in fibromyalgia in recent years has resulted in new evidence-based approaches to pharmacological and nonpharmacological treatment.

Efficacy of milnacipran in the treatment of chronic pain syndromes

Abstract Eleven outpatients with chronic pain syndromes other than fibromyalgia were treated for 12 weeks with milnacipran, a novel serotonin noradrenaline reuptake inhibitor. The agent was administered at 50-150 mg/day, and the mean ± SD dose at 12 weeks or at the time drug treatment was stopped was 84.1 ± 32.2 mg/day. None of the patients met the DSM-IV criteria for a major depressive disorder. Abdominal, chest, back, arm, leg or glossal pain, or headache was involved. Pain was assessed clinically by means of a visual analog scale (VAS) before and 12 weeks after the start of milnacipran treatment, or at the time drug treatment was stopped. The mean ± SD decrease in VAS scores was 42.3 ± 31.6 (50.8 ± 49.2%). One patient discontinued treatment after 4 weeks because of nausea, whereas others tolerated the agent well. These results suggest that the use of milnacipran in patients with a variety of chronic pain syndromes is beneficial.

The relationship between antidepressant and analgesic responses: findings from six placebo-controlled trials assessing the efficacy of duloxetine in patients with major depressive disorder

OBJECTIVE

Debate continues regarding whether onset of analgesia is faster than antidepressant effect in antidepressants with both properties. Duloxetine hydrochloride (from here on referred to as duloxetine) is effective in both major depressive disorder and diabetic peripheral neuropathic pain. This post-hoc analysis of six placebo-controlled duloxetine trials in patients with major depressive disorder was designed to compare onset of antidepressant activity to pain relief.

RESEARCH DESIGN AND METHODS

Duloxetine was administered at 40-120 mg/day versus placebo for up to 9 weeks in outpatient clinic settings. The primary depression measure was the HAMD(17) and pain severity was measured using visual analog scale (VAS) measuring overall pain, headache, back and shoulder pain, and pain while awake. The time course of improvement was profiled using repeated measures modeling and Kaplan-Meier product limit estimation.

RESULTS

In all but one case, significant reductions in HAMD(17) and VAS scores were seen within 2 weeks of treatment. Median time to VAS response was consistently shorter across all VAS measures than that to HAMD(17) response in both placebo- and duloxetine-treated patients with at least modest levels of pain at study entry. Regression analyses consistently demonstrated little association between analgesic and antidepressant responses. Limitations of these findings include that the studies used in these analyses did not require the patients to enroll with any specific level of pain. Moreover, the type of pain exhibiting at presentation was not routinely identified; therefore, the impact of different pain types on these findings is unknown.

CONCLUSIONS

Duloxetine's analgesic effect is independent of the drug's antidepressant effect. Additionally, faster onset of the analgesic effect appears to be a population-specific phenomenon that is unmodified in the presence of active agents.

Depression in the medically ill: diagnostic and therapeutic implications

Depression and medical comorbidities lead to increased morbidity and mortality and have been associated with higher health care costs. Depressive disorders can adversely impact the course of medical illnesses, whereas medical illnesses can serve as a risk factor for future depressive disorders. This interplay has spurred some interesting exploratory research to understand the common pathophysiology and neurobiologic substrates that may explain the bidirectional relationship between the two disorders. There is a paucity of well-designed, randomized, controlled trials to address some of the treatment-related prognostic issues in this population. However, more recent studies have focused on diagnostic and treatment implications with various available pharmacologic and psychotherapeutic modalities. Early identification and appropriate treatment of depression in the medically ill can positively influence medical outcomes and quality of life. Collaborative care models integrating mental health and primary care providers, combined with patient preference, are found to be cost-effective and may result in better response to depression treatment.

Tianeptine: potential influences on neuroplasticity and novel pharmacological effects

Tianeptine is an atypical antidepressant drug. In contrast to tricyclic antidepressants and selective serotonin reuptake inhibitors (SSRIs), it has been suggested that tianeptine decreases serotonin's activity and amount in serotonergic synapses of the central nervous system by increasing serotonin reuptake. Tianeptine, which has a mechanism of action opposite to that of SSRIs, necessitated a re-evaluation of the biochemical basis of depression and revealed that it cannot be explained by the monoamine hypothesis only. Recent studies by tianeptine have been focused on neuroplasticity. Neuroplasticity hypothesis of depression has the potential to make important contributions to the diagnosis, as well as it may be helpful in the explanation of the drug effects, which cannot be explained by neurochemical mechanisms. In addition, recent interesting results indicating anticonvulsant and analgesic activity of tianeptine and its possible interaction with adenosine A(1) receptors were obtained. In this review, novel central actions of tianeptine and the relationship between stress, neuroplasticity and drug effects were evaluated in the light of the current literature.

Change in Pain Severity With Open Label Venlafaxine Use in Patients With a Depressive Symptomatology: An Observational Study in Primary Care

Purpose.

Venlafaxine has shown benefit in the treatment of depression and pain. Worldwide data are extensively lacking investigating the outcome of chronic pain patients with depressive symptoms treated by venlafaxine in the primary care setting. This observational study aimed to elucidate the efficacy of venlafaxine and its prescription by Swiss primary care physicians and psychiatrists in patients with chronic pain and depressive symptomatology.

Subjects and methods.

We studied 505 patients with depressive symptoms suffering from chronic pain in a prospective naturalistic Swiss community based observational trial with venlafaxine in primary care. These patients have been treated with venlafaxine by 122 physicians, namely psychiatrists, general practitioners, and internists.

Results.

On average, patients were treated with 143 ± 75 mg (0–450 mg) venlafaxine daily for a follow-up of three months. Venlafaxine proved to be beneficial in the treatment of both depressive symptoms and chronic pain.

Discussion.

Although side effects were absent in most patients, physicians might have frequently omitted satisfactory response rate of depression by underdosing venlafaxine. Our results reflect the complexity in the treatment of chronic pain in patients with depressive symptoms in primary care.

Conclusion.

Further randomized dose-finding studies are needed to learn more about the appropriate dosage in treating depression and comorbid pain with venlafaxine.

Predictive validity of animal pain models? A comparison of the pharmacokinetic-pharmacodynamic relationship for pain drugs in rats and humans

A number of previous reviews have very eloquently summarized pain models and endpoints in animals. Many of these reviews also discuss how animal models have enhanced our understanding of pain mechanisms and make forward-looking statements as to our proximity to the development of effective mechanism-based treatments. While a number of reports cite failures of animal pain models to predict efficacy in humans, few have actually analyzed where these models have been successful. This review gives a brief overview of those successes, both backward, providing validation of the models, and forward, predicting clinical efficacy. While the largest dataset is presented on treatments for neuropathic pain, this review also discusses acute and inflammatory pain models. Key to prediction of clinical efficacy is a lack of side effects, which may incorrectly suggest efficacy in animals and an understanding of how pharmacokinetic parameters translate from animals to man. As such, this review focuses on a description of the pharmacokinetic-pharmacodynamic relationship for a number of pain treatments that are effective in both animals and humans. Finally we discuss where and why animal pain models have failed and summarize improvements to pain models that should expand and improve their predictive power.

Painful physical symptoms in depression: a clinical challenge

Painful physical symptoms are common elements within mood disorders and provide a therapeutic challenge when such patients attribute their pain to causes other than the mood disorder. These somatic presentations may lead to under-diagnosis and inappropriate treatment of patients with mood disorders. Antidepressant agents that inhibit both serotonin and norepinephrine reuptake effectively remit mood disorders, thereby providing relief of painful physical symptoms often associated with these disorders. They may also provide analgesia for neuropathic pain, such as that caused by diabetic neuropathy, which are associated with mood disorders. Newer generation dual acting antidepressants such as duloxetine and venlafaxine offer a well-tolerated and safe alternative to tricyclics. Concurrent with medication and management, the physician must educate the patient about the nature of both depressed mood and painful physical states that are augmented by and inherent in the depressive disorders. This mini review addresses the problems inherent to the treatment of painful physical symptoms in depression.

No difference in symptoms of irritable bowel syndrome between healthy subjects and patients with recurrent depression in remission

There is bidirectional comorbidity between anxiety/depression and irritable bowel syndrome (IBS). To investigate the prevalence of IBS symptoms, and factors associated with gastrointestinal symptoms in patients with recurrent depressive disorder. Patients (n = 95) with recurrent type of major depression according to DSM-IV criteria and sex- and age-matched controls (n = 190) were sent questionnaires investigating symptoms of IBS [Gastrointestinal Symptom Rating Scale (GSRS)-IBS] and symptoms of anxiety and depression [Hospital Anxiety and Depression Scale (HADS)]. Medical records were checked over a 10-year period for chronic somatic symptoms or diseases. Seventy-three patients with unipolar disorder (mean age 63.6 years SD 13.8; range 23-86 years) and 156 controls (mean age 59.2 years SD 11.6, range 21-85 years) responded. Patients with recurrent depression had higher GSRS-IBS scores and showed a strong correlation between symptoms of IBS and anxiety-depression (r(s) = 0.54; P < 0.001). IBS symptoms were also associated with multiple pain symptoms, higher health-seeking behaviour and selective-serotonin-reuptake inhibitor intake. However, patients with recurrent depression (n = 46) in remission (HADS-Depression score <8) did not have more symptoms of IBS than controls (GSRS-IBS median score 6.0 vs 6.5; P = 0.46). There is a strong association between symptoms of IBS and symptoms of anxiety and depression, whereas depressive patients in remission do not have more IBS symptoms than controls.

Mice lacking central serotonergic neurons show enhanced inflammatory pain and an impaired analgesic response to antidepressant drugs

A large body of literature has implicated serotonin [5-hydroxytryptamine (5-HT)] in descending modulation of nociceptive transmission. Here, we have studied the pain behavior of Lmx1b conditional knock-out mice (Lmx1b(f/f/p)), which lack 5-HT neurons in the CNS. Lmx1b(f/f/p) mutant mice showed normal thermal and visceral pain responses but were less sensitive to mechanical stimuli and exhibited enhanced inflammatory pain compared with their littermate control mice. Importantly, the analgesic effect of several antidepressant drugs, including selective serotonin reuptake inhibitors (SSRIs), serotonin-norepinephrine reuptake inhibitors (SNRIs), and tricyclic antidepressants, was either abolished or greatly attenuated in Lmx1b(f/f/p) mice. Moreover, in the acute versus persistent pain settings, the analgesic actions of the SNRI duloxetine and the SSRI fluoxetine were differentially affected. Together, our results provide in vivo genetic evidence demonstrating that although the predominant role of the central 5-HT system in inflammatory pain is inhibitory, its role in acute mechanical pain is facilitatory. The findings that the analgesic effects of various antidepressant drugs are differentially dependent on the central 5-HT system should help us to understand the mechanism of the analgesic action of different classes of antidepressants in the management of persistent pain.

Duloxetine treatment of pediatric chronic pain and co-morbid major depressive disorder

In the United States, the novel compound duloxetine has been approved for the treatment of major depressive disorder (MDD) and diabetic peripheral neuropathic pain in the adult population. There are currently no published data on the use of duloxetine in children and adolescents. This report describes the successful treatment of 2 adolescent females with chronic pain and co-morbid MDD. Both patients required admission to a tertiary-care pediatric hospital due to the chronicity, severity, and treatment resistance of their pain syndromes. In both cases, duloxetine provided rapid improvement in the experience of pain, as well as mood symptoms, at minimum dosages. Pain symptom reduction and restoration of a euthymic state was maintained at 4- and 3-month follow-up visits, respectively, with minimal to no adverse effects being reported. These cases present preliminary evidence of promising uses for duloxetine in the pediatric population.

Anti-convulsants and anti-depressants

Damage to a nerve should only lead to sensory loss. While this is common, the incidence of spontaneous pain, allodynia and hyperalgesia indicate marked changes in the nervous system that are possible compensations for the loss of normal function that arises from the sensory loss. Neuropathic pain arises from changes in the damaged nerve which then alter function in the spinal cord and the brain and lead to plasticity in areas adjacent to those directly influenced by the neuropathy. The peripheral changes drive central compensations so that the mechanisms involved are multiple and located at a number of sites. Nerve damage increases the excitability of both the damaged and undamaged nerve fibres, neuromas and the cell bodies in the dorsal root ganglion. These peripheral changes are substrates for the ongoing pain and the efficacy of excitability blockers such as carbamazepine, lamotrigine and mexiletine, all anti-convulsants. A better understanding of ion channels at the sites of injury has shown important roles of particular sodium, potassium and calcium channels in the genesis of neuropathic pain. Within the spinal cord, increases in the activity of calcium channels and the receptors for glutamate, especially the N-methyl-D-aspartate (NMDA) receptor, trigger wind-up and central hyperexcitability. Increases in transmitter release, neuronal excitability and receptive field size result from the damage to the peripheral nerves. Ketamine and gabapentin/pregabalin, again with anti-convulsant activity, may interact with these mechanisms. Ketamine acts on central spinal mechanisms of excitability whereas gabapentin acts on a subunit of calcium channels that is responsible for the release of pain transmitters into the spinal cord. In addition to these spinal mechanisms of hyperexcitability, spinal cells participate in a spinal-supraspinal loop that involves parts of the brain involved in affective responses to pain but also engages descending excitatory and inhibitory systems that use the monoamines. These pathways become more active after nerve injury and are the site of action of anti-depressants. This chapter reviews the evidence and mechanisms of drugs, both anti-depressants and anti-convulsants, that are believed to be effective in pain control, with a major emphasis on the neuropathic state.