Desipramine enhances opiate postoperative analgesia

Combined antiallodynic effects of Neurotropin®-tramadol and Neurotropin®-mirogabalin in rats with L5-spinal nerve ligation

We aimed to examine the efficacy of combination therapies of Neurotropin® with tramadol and Neurotropin with mirogabalin for neuropathic pain management. A neuropathic pain model (L5 spinal nerve ligation model: L5-SNL) using male Wistar rats was generated through tight ligation of the left fifth lumbar nerve using silk sutures. Mechanical allodynia was assessed using the 50% paw withdrawal threshold. The combined antiallodynic effects were evaluated using isobolographic analyses. Small intestinal transit was evaluated using the charcoal meal test, and motor coordination using the rota-rod test. Neurotropin (50-200 NU/kg, p.o.), tramadol (7.5-60 mg/kg, p.o.), and mirogabalin (3-30 mg/kg, p.o.) showed a dose-dependent antiallodynic effect in L5-SNL rats. The combined antiallodynic effects of Neurotropin and tramadol were additive or synergistic, whereas those of Neurotropin and mirogabalin were additive. Neurotropin (100-400 NU/kg, p.o.) did not affect the small intestinal transit, whereas tramadol (30-100 mg/kg, p.o.) significantly inhibited it. Neurotropin (100-400 NU/kg, p.o.) did not affect the walking time, whereas mirogabalin (10-100 mg/kg, p.o.) significantly decreased it. Neurotropin dose-dependently ameliorated mechanical allodynia in rats, and combination therapy with Neurotropin-tramadol or Neurotropin-mirogabalin may alleviate neuropathic pain without aggravating the adverse effects of tramadol and mirogabalin.

Tricyclic Antidepressants in Nociceptive and Neuropathic Pain: A Review of Their Analgesic Properties in Combination With Opioids

Objectives: To determine the efficacy and safety of commonly prescribed tricyclic antidepressants (TCAs) as analgesics for nociceptive and neuropathic pain in combination with opioids. Data Sources: A comprehensive literature review was conducted with the assistance of a medical reference librarian on PubMed, MEDLINE, Scopus, and Web of Science using the following search terminology: "Amitriptyline" OR "Doxepin" OR "Desipramine" OR "Imipramine" OR "Nortriptyline" OR "Clomipramine" OR "Trimipramine" AND "Analgesia." Reports of adult patients who received any TCA as an adjunctive analgesic to opioids were included. Study Selection and Data Extraction: A total of 293 results were obtained from the initial database inquiries, following which exclusion criteria were applied and 6 articles were included in this review. Three of the reports detailed the use of TCAs in the perioperative setting, whereas the remaining 3 evaluated their effect on different etiologies of neuropathic pain. Data Synthesis: Tricyclic antidepressants were found to have modest, yet not insignificant, independent analgesic properties, although the ability to provide pain relief was relegated to a select few agents. Desipramine has the most data available for use in nociceptive, postoperative pain through its ability to potentiate and prolong the analgesic effects of opioids and was not associated with adverse drug effects. Conclusions: The efficacy of TCAs for neuropathic pain was not corroborated by this review, and the anticholinergic adverse effects associated with this drug class were found to be significant. Further research is needed to quantify the efficacy of TCAs in the management of nociceptive pain.

LP1 and LP2: Dual-Target MOPr/DOPr Ligands as Drug Candidates for Persistent Pain Relief

Although persistent pain is estimated to affect about 20% of the adult population, current treatments have poor results. Polypharmacology, which is the administration of more than one drug targeting on two or more different sites of action, represents a prominent therapeutic approach for the clinical management of persistent pain. Thus, in the drug discovery process the "one-molecule-multiple targets" strategy nowadays is highly recognized. Indeed, multitarget ligands displaying a better antinociceptive activity with fewer side effects, combined with favorable pharmacokinetic and pharmacodynamic characteristics, have already been shown. Multitarget ligands possessing non-opioid/opioid and opioid/opioid mechanisms of action are considered as potential drug candidates for the management of various pain conditions. In particular, dual-target MOPr (mu opioid peptide receptor)/DOPr (delta opioid peptide receptor) ligands exhibit an improved antinociceptive profile associated with a reduced tolerance-inducing capability. The benzomorphan-based compounds LP1 and LP2 belong to this class of dual-target MOPr/DOPr ligands. In the present manuscript, the structure-activity relationships and the pharmacological fingerprint of LP1 and LP2 compounds as suitable drug candidates for persistent pain relief is described.

Opioid Use in the Postoperative Arena: Global Reduction in Opioids After Surgery Through Enhanced Recovery and Gynecologic Surgery

Enhanced recovery programs aim to reduce surgical stress to improve the patient perioperative experience. Through a combination of multimodal analgesia and maintaining a physiological state, postoperative recovery is improved. Many analgesic adjuncts are available that improve postoperative pain control and limit opioid analgesia requirements. Adjuncts are often used in combination, but different interventions may be incorporated for patient-specific and procedure-specific needs. Postoperative pain control can be optimized by continuing nonopioid adjuncts, and prescribing opioid analgesia to address breakthrough pain. Prescribing practices should balance optimizing pain relief, minimizing the risk of chronic pain, while limiting the potential for opioid misuse.

Antidepressant Drugs for Postsurgical Pain: Current Status and Future Directions

Current treatments for postsurgical pain are often inadequate and adverse effects are substantial such that residual pain and/or side effects impair recovery. The recognition of analgesic efficacy with antidepressant drugs for chronic pain suggests the potential for efficacy in acute postsurgical pain. As reviewed here, current evidence suggests that approximately half of previous trials suggest efficacy of various antidepressants for acute postoperative pain. However, most trials are older with deficiencies including: lack of designation of a primary outcome, no assessment of movement-evoked pain, small size and limited safety assessment. Only one of three trials addressing prevention of chronic postsurgical pain suggested any efficacy; however, the evidence base for this indication is limited. Thus, current evidence does not yet support routine use of any one specific antidepressant for treatment of acute, or prevention of chronic, postsurgical pain. However, limitations in available trials are such that one cannot yet rule out the possibility that one or more antidepressant drugs may provide benefit in specific populations. Therefore, future larger trials should explore optimal dosing and duration of antidepressant treatment, procedure specificity, safety evaluation, and assessment of movement-evoked pain.

Antidepressant drugs for prevention of acute and chronic postsurgical pain: early evidence and recommended future directions

BACKGROUND

This review evaluates trials of antidepressants for acute and chronic postsurgical pain.

METHODS

Trials were systematically identified using predefined inclusion and exclusion criteria. Extracted data included the following: pain at rest and with movement, adverse effects, and other outcomes.

RESULTS

Fifteen studies (985 participants) of early postoperative pain evaluated amitriptyline (three trials), bicifadine (two trials), desipramine (three trials), duloxetine (one trial), fluoxetine (one trial), fluradoline (one trial), tryptophan (four trials), and venlafaxine (one trial). Three studies (565 participants) of chronic postoperative pain prevention evaluated duloxetine (one trial), escitalopram (one trial), and venlafaxine (one trial). Heterogeneity because of differences in drug, dosing regimen, outcomes, and/or surgical procedure precluded any meta-analyses. Superiority to placebo was reported in 8 of 15 trials for early pain reduction and 1 of 3 trials for chronic pain reduction. The majority of positive trials did not report sufficient data to estimate treatment effect sizes. Many studies had inadequate size, safety evaluation/reporting, procedure specificity, and movement-evoked pain assessment.

CONCLUSIONS

There is currently insufficient evidence to support the clinical use of antidepressants-beyond controlled investigations-for treatment of acute, or prevention of chronic, postoperative pain. Multiple positive trials suggest the therapeutic potential of antidepressants, which need to be replicated. Other nontrial evidence suggests potential safety concerns of perioperative antidepressant use. Future studies are needed to better define the risk-benefit ratio of antidepressants in postoperative pain management. Higher-quality trials should optimize dosing, timing and duration of antidepressant treatment, trial size, patient selection, safety evaluation and reporting, procedure specificity, and assessment of movement-evoked pain relevant to postoperative functional recovery.

Relative contributions of norepinephrine and serotonin transporters to antinociceptive synergy between monoamine reuptake inhibitors and morphine in the rat formalin model

Multimodal analgesia is designed to optimize pain relief by coadministering drugs with distinct mechanisms of action or by combining multiple pharmacologies within a single molecule. In clinical settings, combinations of monoamine reuptake inhibitors and opioid receptor agonists have been explored and one currently available analgesic, tapentadol, functions as both a µ-opioid receptor agonist and a norepinephrine transporter inhibitor. However, it is unclear whether the combination of selective norepinephrine reuptake inhibition and µ-receptor agonism achieves an optimal antinociceptive synergy. In this study, we assessed the pharmacodynamic interactions between morphine and monoamine reuptake inhibitors that possess different affinities and selectivities for norepinephrine and serotonin transporters. Using the rat formalin model, in conjunction with measurements of ex vivo transporter occupancy, we show that neither the norepinephrine-selective inhibitor, esreboxetine, nor the serotonin-selective reuptake inhibitor, fluoxetine, produce antinociceptive synergy with morphine. Atomoxetine, a monoamine reuptake inhibitor that achieves higher levels of norepinephrine than serotonin transporter occupancy, exhibited robust antinociceptive synergy with morphine. Similarly, a fixed-dose combination of esreboxetine and fluoxetine which achieves comparable levels of transporter occupancy potentiated the antinociceptive response to morphine. By contrast, duloxetine, a monoamine reuptake inhibitor that achieves higher serotonin than norepinephrine transporter occupancy, failed to potentiate the antinociceptive response to morphine. However, when duloxetine was coadministered with the 5-HT₃ receptor antagonist, ondansetron, potentiation of the antinociceptive response to morphine was revealed. These results support the notion that inhibition of both serotonin and norepinephrine transporters is required for monoamine reuptake inhibitor and opioid-mediated antinociceptive synergy; yet, excess serotonin, acting via 5-HT₃ receptors, may reduce the potential for synergistic interactions. Thus, in the rat formalin model, the balance between norepinephrine and serotonin transporter inhibition influences the degree of antinociceptive synergy observed between monoamine reuptake inhibitors and morphine.

Catechol-O-methyltransferase gene polymorphism and chronic human pain: a systematic review and meta-analysis

In human studies, low COMT (catechol-O-methyltransferase) activity has been associated with increased sensitivity to acute clinical preoperative or postoperative pain. We explored the association between the COMT genotype and three chronic pain conditions: migrainous headache, fibromyalgia, or chronic widespread pain and chronic musculoskeletal pain. Furthermore, we evaluated whether COMT genotype affects the efficacy of opioids in chronic pain. After a systematic literature review, we carried out meta-analyses on the three chronic pain conditions. The efficacy of opioids was evaluated using a systematic review only. The meta-analyses showed that fibromyalgia or chronic widespread pain is the only type of chronic pain that could be associated with the COMT single nucleotide polymorphism rs4680 (Val158Met). Met158, which results in the low-activity variant of COMT, is the risk allele. In chronic clinical pain, the effect of the COMT polymorphism depends on the pain condition. Low COMT activity is not associated with migrainous headache or chronic musculoskeletal pain conditions, but it may increase the risk for fibromyalgia or chronic widespread pain. Low COMT activity increases opioid receptors and enhances opioid analgesia and adverse effects in some cancer pains. Findings from animal studies that have utilized COMT inhibitors elucidate the mechanism behind these findings. In rodent pain models, COMT inhibitors are pronociceptive, except for neuropathic pain models, where nitecapone was found to be antiallodynic. The complex interplay between enhanced adrenergic and dopaminergic activity in different parts of the nociceptive system probably explains the complicated actions of low COMT activity.

Perioperative interventions to reduce chronic postsurgical pain

Approximately 10% of patients following a variety of surgeries develop chronic postsurgical pain. Reducing chronic postoperative pain is especially important to reconstructive surgeons because common operations such as breast and limb reconstruction have even higher risk for developing chronic postsurgical pain. Animal studies of posttraumatic nerve injury pain demonstrate that there is a critical time frame before and immediately after nerve injury in which specific interventions can reduce the incidence and intensity of chronic neuropathic pain behaviors-so called "preventative analgesia." In animal models, perineural local anesthetic, systemic intravenous local anesthetic, perineural clonidine, systemic gabapentin, systemic tricyclic antidepressants, and minocycline have each been shown to reduce pain behaviors days to weeks after treatment. The translation of this work to humans also suggests that brief perioperative interventions may protect patients from developing new chronic postsurgical pain. Recent clinical trial data show that there is an opportunity during the perioperative period to dramatically reduce the incidence and severity of chronic postsurgical pain. The surgeon, working with the anesthesiologist, has the ability to modify both early and chronic postoperative pain by implementing an evidence-based preventative analgesia plan.

[Perioperative adverse events related to antidepressive agents use]

OBJECTIVE

Depression is the most common psychiatric disease, which is treated by the use of antidepressive agents possessing various mechanisms of action. Thus, the use in preoperative period of antidepressive agents is frequent (7% of patients scheduled for surgery). The objective of this review was to update the knowledge on the drug interactions between antidepressive agents and drugs used in perioperative period.

METHODS

(i) Medline and Ovid databases using combination of antidepressive agent and perioperative period as keywords; (ii) national and European epidemiologic database; (iii) expert recommendation and official French health agency; (iv) reference book chapters.

RESULTS

The clinical practice showed a limited risk of adverse event related to antidepressant agents interaction with perioperative used drugs. In the two past decades, few relevant observations of adverse event related with imipramine and monoamine oxidase inhibitors use was reported. The most recent antidepressive agents had no serious adverse interaction. Nevertheless, the serotonin syndrome has to be known as far as it is more and more reported. In case of hypotension, the use of vasopressive agent has to be careful because of excessive response.

Mechanisms of pain transmission and pharmacologic management

BACKGROUND

Pain sensation involves multiple signaling and modulatory pathways, employing a variety of neurotransmitters and other mediators. Inhibitory and facilitatory mechanisms affect the perception of stimuli as painful or non-painful, and in addition may affect the perceived intensity of pain. Endogenous opioids are key mediators in the descending pain suppression pathways. Additionally, monoaminergic neurotransmitters such as norepinephrine, serotonin and dopamine positively or negatively modulate pain signaling, depending on receptor type and location. The various mediators involved in pain signaling provide potential targets for pharmacological interventions. Single analgesic therapies may be limited in their ability to comprehensively target these complex pain signaling pathways. Therapeutic approaches acting on multiple pain transmission pathways through different mechanisms of action provide an opportunity to maximize efficacy and tolerability in the treatment of pain.

SCOPE

This article discusses the various physiologic processes involved in pain signaling and modulation, describes the mechanisms by which various classes of analgesic agents are believed to produce their clinical effects, and explores the potential benefits of a multiple-mechanism approach to analgesia. Published articles describing the physiologic processes involved in pain signaling and modulation and the mechanisms of analgesia for different drug classes were reviewed. MEDLINE searches were conducted to identify relevant studies published through August 2009 that evaluated the efficacy and tolerability of multiple-mechanism analgesic regimens. English language-only randomized controlled trials and meta-analyses of randomized controlled trials were considered.

FINDINGS/CONCLUSION

Multiple neurotransmitters and other mediators are involved in the endogenous modulation of pain signaling, providing numerous opportunities for intervention with different classes of analgesics. Data from numerous clinical trials indicate that multiple-mechanism approaches to analgesia provide comparable or superior analgesic efficacy with lower doses of the individual agents and reduced incidence of side effects. These data support current guidelines which endorse multiple-mechanism strategies for both acute and chronic pain management.

Synergistic interaction between the two mechanisms of action of tapentadol in analgesia

The novel centrally acting analgesic tapentadol [(-)-(1R,2R)-3-(3-dimethylamino-1-ethyl-2-methyl-propyl)-phenol hydrochloride] combines two mechanisms of action, μ-opioid receptor (MOR) agonism and noradrenaline reuptake inhibition (NRI), in a single molecule. Pharmacological antagonism studies have demonstrated that both mechanisms of action contribute to the analgesic effects of tapentadol. This study was designed to investigate the nature of the interaction of the two mechanisms. Dose-response curves were generated in rats for tapentadol alone or in combination with the opioid antagonist naloxone or the α(2)-adrenoceptor antagonist yohimbine. Two different pain models were used: 1) low-intensity tail-flick and 2) spinal nerve ligation. In each model, we obtained dose-effect relations to reveal the effect of tapentadol based on MOR agonism, NRI, and unblocked tapentadol. Receptor fractional occupation was determined from tapentadol's brain concentration and its dissociation constant for each binding site. Tapentadol produced dose-dependent analgesic effects in both pain models, and its dose-effect curves were shifted to the right by both antagonists, thereby providing data to distinguish between MOR agonism and NRI. Both isobolographic analysis of occupation-effect data and a theoretically equivalent methodology determining interactions from the effect scale demonstrated very pronounced synergistic interaction between the two mechanisms of action of tapentadol. This may explain why tapentadol is only 2- to 3-fold less potent than morphine across a variety of preclinical pain models despite its 50-fold lower affinity for the MOR. This is probably the first demonstration of a synergistic interaction between the occupied receptors for a single compound with two mechanisms of action.

A greater role for the norepinephrine transporter than the serotonin transporter in murine nociception

Norepinephrine and serotonin involvement in nociceptive functions is supported by observations of analgesic effects of norepinephrine transporter (NET) and serotonin transporter (SERT) inhibitors such as amitriptyline. However, the relative contribution of NET and SERT to baseline nociception, as well as amitriptyline analgesia, is unclear. Amitriptyline and morphine analgesia in wild-type (WT) mice and littermates with gene knockout (KO) of SERT, NET or both transporters was conducted using the hotplate and tail-flick tests. Hypoalgesia was observed in NET KO mice, and to a lesser extent in SERT KO mice. The magnitude of this hypoalgesia in NET KO mice was so profound that it limited the assessment of drug-induced analgesia. Nonetheless, the necessary exclusion of these subjects because of profound baseline hypoalgesia strongly supports the role of norepinephrine and NET in basal nociceptive behavior while indicating a much smaller role for serotonin and SERT. To further clarify the role of NET and SERT in basal nociceptive sensitivity further experiments were conducted in SERT KO and NET KO mice across a range of temperatures. NET KO mice were again found to have pronounced thermal hypoalgesia compared to WT mice in both the hotplate and tail-flick tests, while only limited effects were observed in SERT KO mice. Furthermore, in the acetic acid writhing test of visceral nociception pronounced hypoalgesia was again found in NET KO mice, but no change in SERT KO mice. As some of these effects may have resulted from developmental consequences of NET KO, the effects of the selective NET blocker nisoxetine and the selective SERT blocker fluoxetine were also examined in WT mice: only nisoxetine produced analgesia in these mice. Collectively these data suggest that NET has a far greater role in determining baseline analgesia, and perhaps other analgesic effects, than SERT in mice.

(–)-(1R,2R)-3-(3-Dimethylamino-1-ethyl-2-methyl-propyl)-phenol Hydrochloride (Tapentadol HCl): a Novel μ-Opioid Receptor Agonist/Norepinephrine Reuptake Inhibitor with Broad-Spectrum Analgesic Properties

(-)-(1R,2R)-3-(3-dimethylamino-1-ethyl-2-methyl-propyl)-phenol hydrochloride (tapentadol HCl) is a novel micro-opioid receptor (MOR) agonist (Ki = 0.1 microM; relative efficacy compared with morphine 88% in a [35S]guanosine 5'-3-O-(thio)triphosphate binding assay) and NE reuptake inhibitor (Ki = 0.5 microM for synaptosomal reuptake inhibition). In vivo intracerebral microdialysis showed that tapentadol, in contrast to morphine, produces large increases in extracellular levels of NE (+450% at 10 mg/kg i.p.). Tapentadol exhibited analgesic effects in a wide range of animal models of acute and chronic pain [hot plate, tail-flick, writhing, Randall-Selitto, mustard oil colitis, chronic constriction injury (CCI), and spinal nerve ligation (SNL)], with ED50 values ranging from 8.2 to 13 mg/kg after i.p. administration in rats. Despite a 50-fold lower binding affinity to MOR, the analgesic potency of tapentadol was only two to three times lower than that of morphine, suggesting that the dual mode of action of tapentadol may result in an opiate-sparing effect. A role of NE in the analgesic efficacy of tapentadol was directly demonstrated in the SNL model, where the analgesic effect of tapentadol was strongly reduced by the alpha2-adrenoceptor antagonist yohimbine but only moderately attenuated by the MOR antagonist naloxone, whereas the opposite was seen for morphine. Tolerance development to the analgesic effect of tapentadol in the CCI model was twice as slow as that of morphine. It is suggested that the broad analgesic profile of tapentadol and its relative resistance to tolerance development may be due to a dual mode of action consisting of both MOR activation and NE reuptake inhibition.

Phase 1A safety assessment of intravenous amitriptyline

The antidepressant amitriptyline is used as an adjuvant in the treatment of chronic pain. Among its many actions, amitriptyline blocks Na+ channels and nerves in several animal and human models. As perioperative intravenous lidocaine has been suggested to decrease postoperative pain, amitriptyline, because of its longer half-life time, might be more useful than lidocaine. However, the use of intravenous amitriptyline is not approved by the US Food and Drug Administration. We therefore investigated the adverse effects of preoperative intravenous amitriptyline in a typical phase 1A trial. After obtaining written Food and Drug Administration and institutional review board approval, we obtained written consent for preoperative infusion of amitriptyline in an open-label, dose-escalating design (25, 50, and 100 mg, n=5 per group). Plasma levels of amitriptyline/nortriptyline were determined, and adverse effects were recorded in a predetermined symptom list. Infusion of 25 and 50 mg amitriptyline appears to be well tolerated; however, the study was terminated when 1 subject in the 100-mg group developed severe bradycardia. Intravenous infusion of amitriptyline (25 to 50 mg over 1 hour) did not create side effects beyond dry mouth and drowsiness, or dizziness, in 2 of our 10 otherwise healthy participants receiving the 25- to 50-mg dose. An appropriately powered future trial is necessary to determine a potential role of amitriptyline in decreasing postoperative pain.

PERSPECTIVE

Amitriptyline potently blocks the persistently open Na+ channels, which are known to be instrumental in various pain states. As this occurs at very low plasma concentrations, a single preoperative intravenous infusion of amitriptyline could provide long-lasting pain relief and decrease the incidence of chronic pain.

Intrathecal administration of doxepin attenuated development of formalin-induced pain in rats

The aim of the present research was to assess the influence of a tricyclic antidepressant doxepin administered intrathecally (i.t.) on the pain behavior in the formalin test (100 microl of 12% formalin was injected into the dorsal part of the hind paw under halotane anesthesia) in male Wistar rats. The influence of doxepin (62.5 microg i.t.) on the pain threshold and number of formalin-induced pain behaviors, as well as antinociceptive effect of morphine was studied. Doxepin significantly increased the nociceptive threshold in the paw pressure test, reduced formalin-induced pain behavior and potentiated morphine antinociceptive effect in formalin test. The obtained results indicate that analgesic effect of doxepin used before the injury is observable at the spinal level after intrathecal treatment, but not only after peripheral administration, which was shown in our previous study. The results of the present research demonstrated a possibility to modify the spinal nociceptive process by administration of doxepin before the formalin injection.

The effect of chronic oral desipramine on capsaicin-induced allodynia and hyperalgesia: a double-blinded, placebo-controlled, crossover study

The tricyclic antidepressants are often used for the treatment of neuropathic pain. In this study, we evaluated one of these drugs on human cutaneous experimental pain. A randomized, double-blinded, placebo-controlled, crossover design methodology was conducted. Subjects participated in 2 14-day study sessions separated by a 7-day washout period. One session was with desipramine and one with placebo. At baseline, Day 7, and Day 15, quantitative sensory testing was performed to thermal and mechanical stimuli. On Day 15 only, intradermal capsaicin was injected on the volar aspect of the forearm followed by an assessment of pain and hyperalgesia. Oral desipramine had no significant effect on acute sensory thresholds, pain, secondary hyperalgesia, or flare response induced by intradermal capsaicin. Mean peak plasma levels of desipramine were within the therapeutic range for the treatment of depression. This study further supports a lack of effect of the tricyclic antidepressants on acute nociception and experimentally-induced secondary hyperalgesia.

IMPLICATIONS

Human experimental pain models have recently been developed; however, the efficacy of the tricyclic antidepressants (TCA) in these models has not been systematically studied. This investigation provides further validation of human experimental pain models and demonstrates that the chronic delivery of a TCA has no effect on human experimental pain.

The psychopharmacologic treatment of depression and anxiety in the context of chronic pain

Chronic pain afflicts millions of people, commonly causing depression and anxiety. These conditions must be treated to achieve a good functional outcome from pain treatment. Selective serotonin reuptake inhibitors, tricyclics, and newer antidepressants effectively treat both depression and selected anxiety disorders. Antidepressants with noradrenergic and serotinergic activity, and anticonvulsants, which may also stabilize mood, are effective in neuropathic pain. Other medications have limited but important pharmacotherapeutic roles.

Evidence-based data on pain relief with antidepressants

This structured review addresses the issue of whether antidepressants have an antinociceptive (analgesic) effect for chronic pain independent of their antidepressant effect. In order to answer this question, human acute pain studies, individual placebo-controlled studies for the treatment of specific chronic pain syndromes, and metaanalytic studies were reviewed and placed into table format. Analysis of this evidence led to the following conclusions: The evidence was consistent in indicating that overall antidepressants may have an antinociceptive effect in chronic pain, and that these drugs were effective for neuropathic pain. There was also some evidence that these drugs could be effective for psychogenic or somatoform disorder-associated pain. This evidence also strongly suggested that serotonergic-noradrenergic antidepressants may have a more consistent antinociceptive effect than the serotonergic antidepressants. Finally, this evidence indicated that antidepressants could be effective for pain associated with some specific pain syndromes, such as chronic low back pain, osteoarthritis or rheumatoid arthritis, fibrositis or fibromyalgia, and ulcer healing. Possible reasons for the conflicting results of studies in this area are presented, and problems that could limit the validity of the conclusions of this review are discussed.

Enhancement of morphine analgesia by the alpha 2-adrenergic antagonist yohimbine

Although interactions between opioids and adrenergic agonists in the treatment of pain have been demonstrated in humans, the contribution of specific adrenergic receptors in this interaction remains to be clarified. In a double-blind, placebo-controlled study in male patients with postoperative dental pain, we investigated the effect of preoperative administration of the alpha 2-adrenergic antagonist, yohimbine, on analgesia produced by postoperative intravenous morphine. Although yohimbine by itself did not affect the pain, the overall analgesic effect of morphine was significantly enhanced in the presence of yohimbine. This report is the first to demonstrate that an alpha 2-adrenergic antagonist enhances opiate analgesia in humans.

Pain responsivity in major depression and bipolar disorder

Signal detection theory measures of thermal pain responsivity were examined in patients with major depression and bipolar disorder and in control subjects. Patients with major depression had significantly poorer sensory discrimination of painful thermal stimuli than control subjects, but they did not differ from the control subjects in their sensory discrimination of warm thermal stimuli of lower intensity. Patients with bipolar disorder did not differ significantly in sensory discrimination from either the patients with major depression or the control subjects. Patients with major depression had significantly higher (i.e., more stoical) response criteria than the control subjects for the painful thermal stimuli and also for the lower intensity stimuli; patients with bipolar disorder had significantly higher criteria than control subjects for only the lower intensity stimuli. The results suggest that reduced responsivity to pain in major depression may reflect sensory as well as affective abnormalities. Complaints of pain are very common in mood disorders, and continued examination of experimental pain in individuals with these disorders has the potential to enhance our understanding of this phenomenon.

Antidepressant drugs as adjuvant analgesics

This article reviews the history of the use of antidepressants in painful states and traces the evolution of thinking from initially considering them as antidepressants to the current concept that they have an analgesic action. The greatest part of this paper considers chronic, nonmalignant, painful states and the evidence with each for the efficacy of some of these drugs. The mechanism of action, pharmacokinetics and adverse effects are discussed. Practical suggestions are made regarding their usage. Although antidepressants are imperfect analgesics because of limited efficacy and untoward effects, they may be the only avenue of relief for a painful condition. The correct choice of agent and proper administration are critical.

Interactions between fluoxetine and opiate analgesia for postoperative dental pain

In a double-blind placebo-controlled study we investigated the analgesic efficacy of combinations of the serotonergic tricyclic antidepressant fluoxetine with either the mu-opiate morphine or the kappa-opiate pentazocine. Administration of oral fluoxetine (10 mg p.o. daily for 7 days pre-operatively) had no effect on the immediate postoperative pain level. However, pre-operative administration of fluoxetine was found, compared to placebo, to antagonize analgesia seen after administration of morphine (6 mg, i.v.) in the immediate postoperative period. Attenuation of morphine analgesia consisted essentially of a shortening of the duration of action of the dose of morphine administered. Similar administration of fluoxetine had no effect on the analgesia produced by the kappa-opiate pentazocine (45 mg, i.v.). This effect probably results from alteration in the known serotonergic circuits in endogenous pain-modulating systems.

Behavioral and neurochemical mechanisms of opioid-antidepressant interactions

Twelve pigeons key-pecked under a multiple variable interval 15-s, 150-s schedule of food reinforcement. The effects of methadone were studied alone and in combination with chronic daily administration of either imipramine (IMI) or desipramine (DMI). Chronic IMI was also given following reductions in response rates by unsignaled delay-to-reinforcement (UDR). Acute administration of methadone produced dose-dependent reductions in response rates under both schedules of reinforcement. Chronic daily administration of IMI or DMI alone did not result in lasting changes in baseline responding. When administered in combination, chronic daily IMI significantly attenuated the rate-reducing effects of methadone, whereas neither a low nor a high dose of chronic daily DMI was effective. The same dose of chronic daily IMI failed to ameliorate response rate reductions under delayed reinforcement. The behavioral and neurochemical specificity of the antidepressant effect is discussed.

Nonopioid agents for treatment of acute and subacute pain

OBJECTIVE

To review the available nonopioid options for alleviating pain.

DESIGN

The various categories of adjuvant agents and their mechanisms of action in the treatment of pain are summarized.

MATERIAL AND METHODS

Adjuvant therapies that directly diminish acute and subacute pain, those that counteract the side effects of opioids, and those that help manage concurrent psychiatric symptoms are discussed, and their recommended doses and adverse effects are outlined.

RESULTS

Adjuvant medications such as nonopioid analgesics (including acetaminophen and nonsteroidal anti-inflammatory drugs), corticosteroids, anticonvulsants, antidepressants, muscle relaxants, and antispasmodics can directly decrease pain. The three most common problems associated with opioid therapy are nausea, constipation, and sedation. Adjuvant drugs such as antiemetics, laxatives, and psychostimulants may counteract these side effects of opioids and thereby enable patients to tolerate adequate doses of opioid agents to relieve pain. In addition, adjuvant medications such as antidepressants, anxiolytics, and antipsychotics can be used to treat concomitant psychiatric symptoms that develop and aggravate existing pain. The choice of agents must be individualized to the patient's particular pain condition; once therapy has been initiated, the response must be continually monitored to optimize control of pain.

CONCLUSION

Nonopioid adjuvant agents should be considered an integral part of the management of acute and subacute pain.

Site- and test-dependent antinociceptive efficacy of amitriptyline in rats

The antinociceptive efficacy of systemic- (IV), spinal- (IT), and global supraspinal (ICV)-administered amitriptyline (AMIT) was compared in three different tests for nociception: the hot-plate test, the tail-flick test, and the withdrawal reflex test. Systemic AMIT inhibited the responses in each of the three tests, with distinct dose-effect relationships. Spinal AMIT reduced in a dose-dependent fashion the force of withdrawal to noxious electrical stimulation but was ineffective in the hot-plate test and facilitated the responses in the tail-flick test. Supraspinal AMIT inhibited in dose-dependent fashion the response to the stimulus of the hot plate, reduced the force of withdrawal after a dose that was effective by the IV route, and again facilitated the responses in the tail-flick test. The results suggest that spinal sites mediate the inhibition of the withdrawal reflex and the supraspinal site the inhibition of the hot-plate test. Two conclusion are drawn: First, AMIT's site of action varies among the pain modalities; and, second, augmentation of the reactions can occur. The complex interaction accords with the clinical experience that the benefits of AMIT in pain treatment are hard to predict.

Temporal factors in the enhancement of morphine analgesia by desipramine

Administration of desipramine, the tricyclic noradrenergic agent, for 7 days pre-operatively, had been found to potentiate postoperative morphine analgesia. In this study we investigated the necessary timing of administration of desipramine in its action to potentiate morphine analgesia. We report that the administration of desipramine for only 3 days, starting 7 days before surgery, also potentiated postoperative morphine analgesia and that the analgesia observed was not different from that in patients receiving a full 7 days of desipramine pre-operatively. The potentiation of morphine analgesia observed was most evident as a prolongation of the analgesic response. Patients who also received desipramine for only 3 days, but starting 3 days pre-operatively had an analgesic response to postoperative morphine that was the same as that in patients receiving placebo. The ability of the administration of desipramine early in the pre-operative week to interact with postoperative morphine and the lack of response when desipramine was given late in the week does not have an explanation at present. However, it may reflect the known latency in humans to the onset of the central effects of tricyclic antidepressants (TCAs).

Low-dose amitriptyline as an adjunct to opioids for postoperative orthopedic pain: a placebo-controlled trial

Tricyclic antidepressants (TCAs) have been found to be useful in the management of a variety of chronic pain conditions, although there is little published regarding the potential efficacy of this class of drug as an adjunct for the control of acute postoperative pain and related symptoms. Twenty-eight patients undergoing total hip or knee arthroplasty completed a randomized, placebo-controlled, double-blinded trial of 50 mg of amitriptyline p.o. HS on postoperative days 1, 2 and 3 while using patient-controlled morphine or meperidine analgesia (PCA). Visual analog (VAS) and numerical verbal (NVS) pain ratings, sedation scores, sleep quantity/quality scores, and sense of well-being scores were assessed twice daily on each of the days succeeding amitriptyline/placebo use. Hourly opioid use was recorded and transcribed from the memory of the PCA devices in use. Mean scores in the amitriptyline group for pain NVS were greater (P < 0.05) (higher score = greater pain) on day 1 and greater on day 2 for the pain VAS. Mean scores for sense of well-being were greater (P < 0.05) (higher score = better sense of well-being) for the placebo group on days 1 and 2. On days 2 and 3, sleep scale variable mean scores were worse in the placebo group (P < 0.025). There were no other statistically significant differences between the control and active drug groups for any of the outcome variables measured. We conclude that amitriptyline at the dose prescribed is no different than placebo in altering the majority of postoperative symptom variables studied in the sample study population but caused no significant adverse effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of a single oral dose of desipramine on postoperative morphine analgesia

Drugs that block norepinephrine reuptake offer promise as opioid potentiators, because norepinephrine mediates opioid analgesia but not side effects such as sedation or nausea. In a two-by-two factorial design, we randomized 62 inpatients with pain following major surgery to receive either desipramine, 50 mg by mouth, or placebo at 6 a.m. on the first day after surgery. At their first request of pain medication after 8 a.m., they were given intravenous morphine, either 0.033 mg/kg or 0.10 mg/kg. Pain relief and side effects were assessed for 4 hr; peak relief on the visual analog scale (VAS) was the primary outcome variable. Pain relief, side effect scores, and time to remedication were significantly greater with the higher dose than with the lower dose of morphine, verifying assay sensitivity, but desipramine pretreatment did not significantly enhance morphine analgesia. The mean increase in peak VAS relief score after desipramine pretreatment, relative to placebo, was 6%; the 95% confidence interval for this estimate ranged from a 21% reduction to a 34% increase in pain relief. These results differ from a previous report that 1 week of pretreatment with desipramine, 75 mg per day, potentiated postoperative morphine analgesia. We conclude that if desipramine potentiation of opioid analgesia occurs in humans, its demonstration may require higher doses or chronic treatment.

Enhancement of pentazocine analgesia by clonidine

Opiate-adrenergic interactions were investigated by studying the effect of the selective alpha 2-adrenergic agonist, clonidine, on the analgesia produced by intravenous placebo and by the predominantly kappa-opiate agonist, pentazocine, in patients with dental postoperative pain. Clonidine did not affect the pain level when administered with intravenous placebo. When administered with pentazocine, clonidine caused a statistically significant increase in pentazocine analgesia. Comparison is made to other opiate-adrenergic interactions and possible mechanisms are discussed.

Lack of effect of ephedrine on opiate analgesia

Opiate-adrenomimetic interaction was investigated by studying the effect of the adrenomimetic agent, ephedrine, on the analgesia produced by intravenous placebo and that produced by the predominantly kappa opiate agonist, pentazocine, in patients with dental postoperative pain. Ephedrine did not significantly affect the analgesia of intravenous placebo or of pentazocine. These results contrast with earlier studies demonstrating enhancement of opiate analgesia by other adrenomimetics. Further clinical studies are needed to delineate the specificity of opiate-adrenomimetic interaction.

L-tryptophan supplementation does not affect postoperative pain intensity or consumption of analgesics

Aiming at optimizing serotonin levels in endogenous pain-modulating systems, L-tryptophan supplementation pre- and postoperatively (2 g/day for 7 days) did not affect pain development or analgesic consumption after third molar surgery. Biological effects related to an increase in mood were observed, however, indicating transport of L-tryptophan to the central nervous system. The findings are discussed in relation to earlier reports on favorable effects of L-tryptophan on experimental pain in healthy subjects and in chronic pain patients.

Effects on opioid-induced rate reductions by doxepin and bupropion

Twelve pigeons key-pecked under a multiple variable interval 15-second, variable interval 150-second schedule of food reinforcement. Effects of two opioid drugs, buprenorphine and methadone, were determined alone and in combination with chronic daily administration of the antidepressants doxepin or bupropion. Methadone initially produced dose-dependent key-pecking rate reductions when administered acutely, prior to the session, while buprenorphine produced key-pecking rates that reached a plateau at 50-80% of baseline rate and were not reduced further by higher doses. Neither doxepin nor bupropion, given alone, had lasting effects on key-pecking rates. Chronic daily doxepin administration significantly attenuated methadone-induced response rate reductions. Bupropion reduced the effect of the highest methadone dose, but this effect was mitigated by the development of opioid tolerance. Unlike bupropion, doxepin interfered with the development of opioid tolerance. Neither antidepressant systematically altered effects of buprenorphine on key-pecking.

Intrathecal administration of thiorphan, bestatin, desipramine and fluoxetine differentially potentiate the antinociceptive effects induced by beta-endorphin and morphine, administered intracerebroventricularly

The effects of the intrathecal injection of thiorphan (an inhibitor of enkephalinase inhibitor), bestatin (an inhibitor of aminopeptidase), desipramine (an inhibitor of the uptake of noradrenaline) and fluoxetine (an inhibitor of the uptake of serotonin) on the antinociception induced by beta-endorphin and morphine, administered intracerebroventricularly, were studied in male ICR mice. Antinociceptive effects were assessed by the tail-flick and hot-plate tests. Thiorphan (16 micrograms) and bestatin (16 micrograms), injected intrathecally, potentiated inhibition of the tail-flick response, induced by beta-endorphin but not by morphine administered intracerebroventricularly, whereas desipramine (6 micrograms) and fluoxetine (6 micrograms), injected intrathecally potentiated inhibition of the tail-flick response induced by morphine, but not by beta-endorphin, administered intracerebroventricularly. Thiorphan, bestatin, desipramine or fluoxetine, given intrathecally, did not antagonize inhibition of the hot-plate response, induced by beta-endorphin or morphine administered intracerebroventricularly. The results indicate that inhibition of the tail-flick response, induced by beta-endorphin administered intracerebroventricularly, is mediated by the opioid system, but not by noradrenergic and serotonergic systems in the spinal cord. On the other hand, the inhibition of the tail-flick response, induced by morphine given intracerebroventricularly, is mediated by noradrenergic and serotonergic systems, but not by the opioid system in the spinal cord. The lack of effect of enzyme inhibitors and inhibitors of the uptake of biogenic amines intrathecally on beta-endorphin- and morphine-induced inhibition of the hot-plate response, is due to the supraspinal nature of the nociceptive hot-plate response. The present results further support the hypothesis, proposed previously, that intracerebroventricularly injected beta-endorphin and morphine elicit antinociception by activating different descending inhibitory systems.

Noradrenergic and opioidergic influences on the antinociceptive effect of clomipramine in the formalin test in rats

Although tricyclic antidepressants are especially useful in the treatment of chronic pain conditions, most of the work about its mechanism of action has been made on acute pain tests. The present study was aimed at studying the role played by noradrenergic and opioidergic influences on the antinociceptive activity of subchronically administered clomipramine in the formalin test (a tonic pain model) in rats. Clomipramine produced antinociception after 7 days, administration (2.5 mg/kg/day), an effect equivalent to that obtained by acute morphine (5 mg/kg). The antinociceptive effect of clomipramine was inhibited by the following: nonspecific blocking of alpha 1- and alpha 2-adrenoceptors by phentolamine, specific blocking of alpha 1-adrenoceptors by prazosin; stimulation of alpha 2 receptors by clonidine; and blocking of the opioid receptors by naloxone. Blocking the alpha 2-receptors with yohimbine did not antagonize the effect of clomipramine. These results suggest that clomipramine produces antinociception in this test, partly via the participation of the endogenous opioid system and partly by further activating or potentiating previously activated noradrenergic pathways which are involved in the control of pain information.

Modification of the antinociceptive effect of morphine by acute and chronic administration of clomipramine in mice

The antinociception effect of clomipramine and the combination of clomipramine and morphine was evaluated using the constant temperature hot plate test, the increasing temperature hot plate test and the formalin test in mice. Both a single dose of clomipramine (10 mg/kg) given intraperitoneally (i.p.) and chronic clomipramine treatment (10 mg/kg/day, i.p., for 7 days) induced antinociception. When morphine (5 mg/kg), given subcutaneously (s.c.), and clomipramine were combined, an increased antinociceptive effect compared to morphine alone was observed in all tests. In the increased temperature hot plate test and in the formalin test increased antinociception was also observed when morphine was combined with chronic clomipramine treatment. In the constant temperature hot plate test no additional effect compared to morphine alone was observed when morphine and chronic clomipramine treatment were combined. These results indicate that clomipramine has an antinociceptive effect in itself, and that it may enhance the antinociceptive effects of morphine. The differences between the tests indicate that different nociceptive mechanisms are involved, and that the combination of clomipramine and morphine may be beneficial for some types of nociceptive stimuli, but not for others.