Morphine responses and experimental pain: sex differences in side effects and cardiovascular responses but not analgesia

Effects of Savoring Meditation on Positive Emotions and Pain-Related Brain Function: A Mechanistic Randomized Controlled Trial in People With Rheumatoid Arthritis

Positive emotions are a promising target for intervention in chronic pain, but mixed findings across trials to date suggest that existing interventions may not be optimized to efficiently engage the target. The aim of the current pilot mechanistic randomized controlled trial was to test the effects of a positive emotion-enhancing intervention called Savoring Meditation on pain-related neural and behavioral targets in patients with rheumatoid arthritis. Participants included 44 patients with a physician-confirmed diagnosis of rheumatoid arthritis (n = 29 included in functional magnetic resonance imaging (fMRI) analyses), who were randomized to either Savoring Meditation or a Slow Breathing control. Both meditation interventions were brief (four 20-minute sessions). Self-report measures were collected pre-and post-intervention. An fMRI task was conducted at post-intervention, during which participants practiced the meditation technique on which they had been trained while exposed to non-painful and painful thermal stimuli. Savoring significantly reduced experimental pain intensity ratings relative to rest (P < .001). Savoring also increased cerebral blood flow in the ventromedial prefrontal cortex and increased connectivity between the ventromedial prefrontal cortex and caudate during noxious thermal stimulation relative to Slow Breathing (z = 2.3 voxelwise, false discovery rate cluster corrected P = .05). Participants in the Savoring condition also reported significantly increased positive emotions (ps < .05) and reduced anhedonic symptoms (P < .01) from pre- to post-intervention. These findings suggest that Savoring recruits reward-enhancing corticostriatal circuits in the face of pain, and future work should extend these findings to evaluate if these mechanisms of Savoring are associated with improved clinical pain outcomes in diverse patient populations. PERSPECTIVE: Savoring Meditation is a novel positive emotion-enhancing intervention designed for patients with chronic pain. The present findings provide preliminary evidence that Savoring Meditation is acutely analgesic, and engages neural and subjective emotional targets that are relevant to pain self-management. Future work should evaluate the clinical translation of these findings.

Risk factors for discontinuing intravenous patient-controlled analgesia after thoracic surgery

PURPOSE

This study examined the risk factors of experiencing side effects from using intravenous patient-controlled analgesia (IV PCA) following lung and esophageal surgery.

METHODS

Our study included adult patients who underwent lung or esophageal surgery and received IV PCA for postoperative acute pain control between 2020 and 2022. We collected information on side effects from IV PCA use, the decision to discontinue PCA, and the PCA regimen from the daily reports of the acute pain management team and verified the accuracy using electronic records from ward nurses. The primary outcome was the risk factor associated with discontinuing IV PCA due to its side effects.

RESULTS

Out of the 1796 patients in our study, 1795 used PCA containing opioids; 196 patients stopped IV PCA due to unbearable side effects. Being female (adjusted odds ratio [aOR]: 2.65, 95% confidence interval [CI]: 1.70, 4.13) was linked to a higher chance of stopping PCA use. Having hypertension (aOR: 0.46, 95% CI: 0.26, 0.81) and being classified as the American Society of Anesthesiologists class 3 or higher (aOR: 0.48, 95% CI: 0.23, 0.86) were associated with a lower chance of discontinuing PCA use.

CONCLUSION

Our study determined the risk factors to stop using IV PCA due to side effects following lung or esophageal surgery. These results emphasize the need for personalized pain management plans that take into account the patient's characteristics and the type of surgery performed.

Effect of gene variants on opioid dose, pain and adverse effect outcomes in advanced cancer: an explorative study

Aim: Associations between gene variants and opioid net effect are unclear. We conducted an exploratory pharmacogenetic analysis of 35 gene variants and opioid response in advanced cancer. Patients & methods: This multi-center prospective cohort study included clinical data, questionnaires (pain and adverse effects) and DNA (blood). Negative binomial regression and logistic regression were used. Results: Within 54 participants, eight statistically significant associations (p = 0.002-0.038) were observed between gene variants and opioid dose, pain scores or adverse effects, the majority being within the neuroimmune TLR4 pathway (IL1B [rs1143634], IL2 [rs2069762], IL6 [rs1800795], BDNF [rs6265]) and ARRB2 pathway (ARRB2 [rs3786047], DRD2 [rs6275]). Conclusion: Neuroimmune pathway genes may contribute to differences in opioid response in cancer and may be included in future similar studies.

Effects of Savoring Meditation on Positive Emotions and Pain-Related Brain Function: A Mechanistic Randomized Controlled Trial in People With Rheumatoid Arthritis

Positive emotions are a promising target for intervention in chronic pain, but mixed findings across trials to date suggest that existing interventions may not be optimized to efficiently engage the target. The aim of the current mechanistic randomized controlled trial was to test the effects of a single skill positive emotion-enhancing intervention called Savoring Meditation on pain-related neural and behavioral targets in patients with rheumatoid arthritis (RA). Participants included 44 patients with a physician-confirmed diagnosis of RA (n=29 included in fMRI analyses), who were randomized to either Savoring Meditation or a Slow Breathing control. Both meditation interventions were brief (four 20-minute sessions). Self-report measures were collected pre- and post-intervention. An fMRI task was conducted at post-intervention, during which participants practiced the meditation technique on which they had been trained while exposed to non-painful and painful thermal stimuli. Relative to Slow Breathing, Savoring significantly reduced experimental pain intensity ratings relative to rest (p<.001), increased cerebral blood flow in the ventromedial prefrontal cortex (vmPFC) and increased connectivity between the vmPFC and caudate during noxious thermal stimulation (z=2.3 voxelwise, FDR cluster corrected p=0.05). Participants in the Savoring condition also reported significantly increased positive emotions (ps<.05) and reduced anhedonic symptoms (p<.01) from pre- to post-intervention. These findings suggest that that Savoring recruits reward-enhancing corticostriatal circuits in the face of pain, and future work should extend these findings to evaluate if these mechanisms of Savoring are associated with improved clinical pain outcomes in diverse patient populations.

Effects of morphine and P2Y inhibitor amongst patients with acute coronary syndrome: A meta-analysis of comparative studies

BACKGROUND

P2Y inhibitor and morphine are widely used in caring for patients with the acute coronary syndrome (ACS), but there are some concerns about the combination use due to interaction in metabolism. Therefore, this study aimed to examine whether using morphine with antiplatelets in patients with ACS affects the clinical outcomes based on currently available evidence.

METHODS

Three databases were searched for comparative studies on this topic by using relevant keywords of ACS and morphine. Two authors independently extracted study information, mortality, major adverse cardiac event (MACE), major bleeding, and length of hospital stay. Then, they evaluated the quality of evidence independently. Meta-analysis was planned to be conducted in random-effects model. Risk ratio (RR) was used for most outcomes except hospital stay, and Peto odds ratio (POR) was used if there were any zero cells. Pooled estimate was presented with 95% confidence interval (CI).

RESULTS

Fourteen studies (n = 73,033) met eligibility criteria, and there was non-significant difference in mortality between antiplatelet with and without morphine (RR = 1.13, 95%CI: 0.78 to 1.64). Antiplatelet therapy without morphine significantly reduced the risk of MACE (RR = 0.78, 95%CI: 0.67 to 0.89; I-square = 0%), but increased the odds of major bleeding (POR = 1.87, 95%CI: 1.04 to 3.35; I-square = 0%) as compared with the combined use of antiplatelet therapy and morphine.

CONCLUSION

In conclusion, there is no statistically significant difference in mortality in patients with ACS using morphine or not, but clinicians ought to make a trade-off between a lower risk of MACE and a higher risk of major bleeding before adding morphine to antiplatelet therapy.

A systematic review on sex differences in adverse drug reactions related to psychotropic, cardiovascular, and analgesic medications

Background and objective: Adverse drug reactions (ADRs) are the main safety concerns of clinically used medications. Accumulating evidence has shown that ADRs can affect men and women differently, which suggests sex as a biological predictor in the risk of ADRs. This review aims to summarize the current state of knowledge on sex differences in ADRs with the focus on the commonly used psychotropic, cardiovascular, and analgesic medications, and to aid clinical decision making and future mechanistic investigations on this topic. Methods: PubMed search was performed with combinations of the following terms: over 1,800 drugs of interests, sex difference (and its related terms), and side effects (and its related terms), which yielded over 400 unique articles. Articles related to psychotropic, cardiovascular, and analgesic medications were included in the subsequent full-text review. Characteristics and the main findings (male-biased, female-biased, or not sex biased ADRs) of each included article were collected, and the results were summarized by drug class and/or individual drug. Results: Twenty-six articles studying sex differences in ADRs of six psychotropic medications, ten cardiovascular medications, and one analgesic medication were included in this review. The main findings of these articles suggested that more than half of the ADRs being evaluated showed sex difference pattern in occurrence rate. For instance, lithium was found to cause more thyroid dysfunction in women, and amisulpride induced prolactin increase was more pronounced in women than in men. Some serious ADRs were also found to exert sex difference pattern, such as clozapine induced neutropenia was more prevalent in women whereas simvastatin/atorvastatin-related abnormal liver functions were more pronounced in men.

Sex differences in the impact of pain, morphine administration and morphine withdrawal on quality of life in rats

The disruptive effects of pain on quality of life are greater in men than in women, but the disruptive effects of opioid administration and withdrawal tend to be greater in women. These sex differences in pain, acute opioid effects, and opioid withdrawal tend to be opposite to sex differences reported in laboratory rats. We hypothesized that sex differences in humans and rats would more closely align if animal research measured quality of life as opposed to traditional evoked behaviors of pain (e.g., nociceptive reflexes) and opioid withdrawal (e.g., wet dog shakes). The present study assessed quality of life in adult female and male rats by measuring voluntary wheel running in the rat's home cage. Hindpaw inflammation induced by administration of Complete Freund's Adjuvant (CFA) into the right hindpaw caused a greater depression of wheel running in male compared to female rats. Twice daily injections of high morphine doses (5-20 mg/kg) and the subsequent morphine withdrawal caused a greater depression of wheel running in female compared to male rats. These sex differences are consistent with human data that shows the impact of pain on quality of life is greater in men than women, but the negative effects of opioid administration and withdrawal are greater in women. The present data indicate that the clinical significance of animal research would be enhanced by shifting the endpoint from pain and opioid evoked behaviors to measures of quality of life such as voluntary wheel running.

Low-dose morphine reduces tolerance to central hypovolemia in healthy adults without affecting muscle sympathetic outflow

Hemorrhage is a leading cause of preventable battlefield and civilian trauma deaths. Low-dose (i.e., an analgesic dose) morphine is recommended for use in the prehospital (i.e., field) setting. Morphine administration reduces hemorrhagic tolerance in rodents. However, it is unknown whether morphine impairs autonomic cardiovascular regulation and consequently reduces hemorrhagic tolerance in humans. Thus, the purpose of this study was to test the hypothesis that low-dose morphine reduces hemorrhagic tolerance in conscious humans. Thirty adults (15 women/15 men; 29 ± 6 yr; 26 ± 4 kg·m-2, means ± SD) completed this randomized, crossover, double-blinded, placebo-controlled trial. One minute after intravenous administration of morphine (5 mg) or placebo (saline), we used a presyncopal limited progressive lower-body negative pressure (LBNP) protocol to determine hemorrhagic tolerance. Hemorrhagic tolerance was quantified as a cumulative stress index (mmHg·min), which was compared between trials using a Wilcoxon matched-pairs signed-rank test. We also compared muscle sympathetic nerve activity (MSNA; microneurography) and beat-to-beat blood pressure (photoplethysmography) during the LBNP test using mixed-effects analyses [time (LBNP stage) × trial]. Median LBNP tolerance was lower during morphine trials (placebo: 692 [473-997] vs. morphine: 385 [251-728] mmHg·min, P < 0.001, CI: -394 to -128). Systolic blood pressure was 8 mmHg lower during moderate central hypovolemia during morphine trials (post hoc P = 0.02; time: P < 0.001, trial: P = 0.13, interaction: P = 0.006). MSNA burst frequency responses were not different between trials (time: P < 0.001, trial: P = 0.80, interaction: P = 0.51). These data demonstrate that low-dose morphine reduces hemorrhagic tolerance in conscious humans. Thus, morphine is not an ideal analgesic for a hemorrhaging individual in the prehospital setting.NEW & NOTEWORTHY In this randomized, crossover, placebo-controlled trial, we found that tolerance to simulated hemorrhage was lower after low-dose morphine administration. Such reductions in hemorrhagic tolerance were observed without differences in MSNA burst frequency responses between morphine and placebo trials. These data, the first to be obtained in conscious humans, demonstrate that low-dose morphine reduces hemorrhagic tolerance. Thus, morphine is not an ideal analgesic for a hemorrhaging individual in the prehospital setting.

Low-Dose Morphine Reduces Pain Perception and Blood Pressure, but Not Muscle Sympathetic Outflow, Responses During the Cold Pressor Test

Our knowledge about how low-dose (analgesic) morphine affects autonomic cardiovascular regulation is primarily limited to animal experiments. Notably, it is unknown if low-dose morphine affects human autonomic cardiovascular responses during painful stimuli in conscious humans. Therefore, we tested the hypothesis that low-dose morphine reduces perceived pain and subsequent sympathetic and cardiovascular responses in humans during an experimental noxious stimulus. Twenty-nine participants (14F/15M; 29±6 y; 26±4 kg•m^-2, mean ± SD) completed this randomized, crossover, placebo-controlled trial during two laboratory visits. During each visit, participants completed a cold pressor test (CPT; hand in ~0.4 °C ice bath for two minutes) before and ~35 minutes after drug/placebo administration (5 mg IV morphine or saline). We compared pain perception (100 mm visual analog scale), muscle sympathetic nerve activity (MSNA; microneurography; 14 paired recordings), and beat-to-beat blood pressure (BP; photoplethysmography) between trials (at both pre- and post-drug/placebo time points) using paired, two-tailed t-tests. Before drug/placebo infusion, perceived pain (p=0.92), Δ MSNA burst frequency (n=14, p=0.21), and Δ mean BP (p=0.39) during the CPT were not different between trials. After the drug/placebo infusion, morphine versus placebo attenuated perceived pain (morphine: 43±20 vs. placebo: 57±24 mm,p<0.001) and Δ mean BP (morphine: 10±7 vs. placebo: 13±8 mmHg,p=0.003), but not Δ MSNA burst frequency (morphine: 10±11 vs. placebo: 13±11 bursts/minute,p=0.12), during the CPT. Reductions in pain perception and Δ mean BP were only weakly related (r=0.34,p=0.07; post-morphine CPT minus post-placebo CPT). These data provide valuable information regarding how low-dose morphine affects autonomic cardiovascular responses during an experimental painful stimulus.

Sex-Related Differences in Pharmacological Response to CNS Drugs: A Narrative Review

In the last decades, both animal and human studies have neglected female subjects with the aim of evading a theorized intricacy of feminine hormonal status. However, clinical experience proves that pharmacological response may vary between the two sexes since pathophysiological dissimilarities between men and women significantly influence the pharmacokinetics and pharmacodynamics of drugs. Sex-related differences in central nervous system (CNS) medication are particularly challenging to assess due to the complexity of disease manifestation, drugs’ intricate mechanisms of action, and lack of trustworthy means of evaluating the clinical response to medication. Although many studies showed contrary results, it appears to be a general tendency towards a certain sex-related difference in each pharmacological class. Broadly, opioids seem to produce better analgesia in women especially when they are administered for a prolonged period of time. On the other hand, respiratory and gastrointestinal adverse drug reactions (ADRs) following morphine therapy are more prevalent among female patients. Regarding antidepressants, studies suggest that males might respond better to tricyclic antidepressants (TCAs), whereas females prefer selective serotonin reuptake inhibitors (SSRI), probably due to their tolerance to particular ADRs. In general, studies missed spotting any significant sex-related differences in the therapeutic effect of antiepileptic drugs (AED), but ADRs have sex variations in conjunction with sex hormones’ metabolism. On the subject of antipsychotic therapy, women appear to have a superior response to this pharmacological class, although there are also studies claiming the opposite. However, it seems that reported sex-related differences regarding ADRs are steadier: women are more at risk of developing various side effects, such as metabolic dysfunctions, cardiovascular disorders, and hyperprolactinemia. Taking all of the above into account, it seems that response to CNS drugs might be occasionally influenced by sex as a biological variable. Nonetheless, although for each pharmacological class, studies generally converge to a certain pattern, opposite outcomes are standing in the way of a clear consensus. Hence, the fact that so many studies are yielding conflicting results emphasizes once again the need to address sex-related differences in pharmacological response to drugs.

Gender Differences in Medication Adverse Effects Experienced by People Living With Chronic Pain

Objectives

Understanding gender differences in chronic pain (CP) outcome research is essential to optimal treatment delivery. This study explored the associations between gender identity, gender roles, and the number of non-life-threatening pain medication adverse effects reported as severe by people living with CP.

Methods

The analyses were conducted using the COPE Cohort, a dataset generated through a web-based recruitment of adults with CP. Participants were asked how they identified themselves (women, men, unknown, unspecified) and gender roles were measured using the Bem Sex-Role Inventory (subgroups were formed applying the median split method). Pain medication adverse effects were assessed using a standardized checklist (none/mild/moderate/severe). A zero-inflated Poisson model was used to assess gender identity, gender roles and their interaction as potential predictors of the number of pain medication adverse effects.

Results

A total of 1,343 participants reported using pain medications. Adjusting for potential confounders, both gender identity (men vs. women: ß = −0.32, p = 0.0024) and gender roles (androgynous vs. undifferentiated: ß = 0.26, p = 0.0030) were associated with the number of pain medication adverse effects reported as severe, and they interacted with each other. The stratified analysis by gender roles showed that women reported a greater number of severe adverse effects than men among those classified as masculine and androgynous.

Discussion

Although we are unable to confirm whether the associations can be explained by differences in the experience or in the reporting of effects, gender identity and gender roles should both be explored when studying pain medication adverse effects.

Sex differences in opioid receptor mediated effects: Role of androgens

An abundance of data indicates there are sex differences in endogenous opioid peptides and opioid receptors, leading to functional differences in sensitivity to opioid receptor mediated behaviors between males and females. Many of these sex differences are mediated by the effects of gonadal hormones on the endogenous opioid system. Whereas much research has examined the role of ovarian hormones on opioid receptor mediated endpoints, comparatively less research has examined the role of androgens. This review describes what is currently known regarding the influence of androgens on opioid receptor mediated endpoints and how androgens may contribute to sex differences in these effects. The review also addresses the clinical implications of androgenic modulation of opioid receptor mediated behaviors and suggests future lines of research for preclinical and clinical investigators. We conclude that further investigation into androgenic modulation of opioid receptor mediated effects may lead to new options for addressing conditions such as chronic pain and substance use disorders.

Prescription Opioid Use Among a Community Sample of Older and Younger Women

Background: Women bear a heavier burden of the consequences related to prescription opioid use compared to their male counterparts; however, there has been little attention in the literature regarding prescription opioid use among women. We aimed to examine risk factors for prescription opioid use among women. Methods: Demographics, health status, and substance use data, including prescription opioid use, were collected through a community engagement program, HealthStreet, during a health needs assessment. Women older than 18 years were classified by opioid use: past 30-day, lifetime, but not past 30-day, or no lifetime prescription opioid use. Descriptive statistics and chi-square tests were calculated, and multinomial logistic regression was used to calculate adjusted odds ratios (aORs; confidence interval [CI]). Results: Among 5,549 women assessed, 15% reported past 30-day use and 41% reported lifetime use of prescription opioids. While prescription sedative use was the strongest risk factor for past 30-day use among younger women (aOR = 4.84; 95% CI, 3.59-6.51), past 6-month doctor visits was the strongest risk factor for past 30-day use among older women (aOR = 4.15; 95% CI, 2.62-6.60). Conclusions: We found higher rates of prescription opioid use in this community sample of women compared to national rates. Risk factors for recent prescription opioid use (past 30-day use) differed among older and younger women. Clinicians should be more vigilant about prescribing opioids as the medical profile for women may change through age, especially the co-prescribing of opioids and sedatives.

Opioids for chronic pain management in patients with dialysis-dependent kidney failure

Chronic pain is highly prevalent among adults treated with maintenance haemodialysis (HD) and has profound negative effects. Over four decades, research has demonstrated that 50-80% of adult patients treated with HD report having pain. Half of patients with HD-dependent kidney failure (HDKF) have chronic moderate-to-severe pain, which is similar to the burden of pain in patients with cancer. However, pain management in patients with HDKF is often ineffective as most patients report that their pain is inadequately treated. Opioid analgesics are prescribed more frequently for patients receiving HD than for individuals in the general population with chronic pain, and are associated with increased morbidity, mortality and health-care resource use. Furthermore, current opioid prescribing patterns are frequently inconsistent with guideline-recommended care. Evidence for the effectiveness of opioids in pain management in general, and in patients with HDKF specifically, is lacking. Nonetheless, long-term opioid therapy has a role in the treatment of some patients when used selectively, carefully and combined with an ongoing assessment of risks and benefits. Here, we provide a comprehensive overview of the use of opioid therapy in patients with HDKF and chronic pain, including a discussion of buprenorphine, which has potential as an analgesic option for patients receiving HD owing to its unique pharmacological properties.

No antinociceptive synergy between morphine and delta-9-tetrahydrocannabinol in male and female rats with persistent inflammatory pain

Studies have demonstrated antinociceptive synergy between morphine and delta-9-tetrahydrocannabinol (THC) in animals, but whether such synergy occurs against all types of pain and in humans is unclear. Because a majority of chronic pain patients are women, and sex differences in morphine and THC potencies have been observed in rodents, the present study examined sex-specific effects of morphine and THC given alone and in combination, in rats with persistent inflammatory pain. On day 1, baseline mechanical and thermal response thresholds, hindpaw weight-bearing, locomotor activity, and hindpaw thickness were determined. Inflammation was then induced via hindpaw injection of complete Freund's adjuvant (CFA). Three days later, morphine (s.c.), THC (i.p) or a morphine-THC combination (1:1, 3:1 and 1:3 dose ratios) was administered, and behavioral testing was conducted at 30-240 min postinjection. Morphine alone was antiallodynic and antihyperalgesic, with no sex differences, but at some doses increased weight-bearing on the CFA-treated paw more in males than females. THC alone reduced mechanical allodynia with similar potency in both sexes, but reduced thermal hyperalgesia and locomotor activity with greater potency in females than males. All morphine-THC combinations reduced allodynia and hyperalgesia, but isobolographic analysis of mechanical allodynia data showed no significant morphine-THC synergy in either sex. Additionally, whereas morphine alone was antinociceptive at doses that did not suppress locomotion, morphine-THC combinations suppressed locomotion and did not increase weight-bearing on the inflamed paw. These results suggest that THC is unlikely to be a beneficial adjuvant when given in combination with morphine for reducing established inflammatory pain.

Gender response to 10 weeks acupuncture-TENS application on patients who presented with post-injection sciatic pain

Background

Studies to determine gender response to transcutaneous electrical nerve stimulation (TENS) application on individuals who presented with post-injection sciatic pain (PISP) following gluteal injection is not common. A total of 40 subjects comprising 20 males and 20 females who were purposively recruited and conveniently assigned to group A (male) and group B (female) completed the study. Acupuncture-like TENS (AL-TENS) was applied on the 20 male and 20 female subjects, 1 h per session, 3 times per week for the 10 weeks the study lasted.

Result

The pre-intervention baseline scores for the two groups were 8.80 + 1.05 (Female) and 8.60 + 1.27 (Male). The result revealed that after 10 weeks of intervention the VAS scores were 2.60+ 3.28 (p < 0.001) and 2.40 + 3.28 (p < 0.001) for the female and male subjects, respectively. The mean comparison of the female mean VAS scores (2.60 + 3.28) and male VAS scores 2.40 + 3.25 after 10 weeks of AL-TENS intervention shows no statistically significant difference (p > 0.85) in pain intensity (pain perception).

Conclusions

There was no gender variation in pain perception in subjects with post-injection sciatic pain (PISP) following gluteal muscle injection after 10 weeks of AL-TENS application. Therefore, gender-based variation should not be considered when applying AL-TENS as an instrument of intervention in subjects with PISP.

Trial registration

PACTR2018050034082

Sex and Estrous Cycle Differences in Analgesia and Brain Oxycodone Levels

Sex differences in opioid analgesia occur in rodents and humans, and could be due to differences in drug and metabolite levels. Thus, we investigated the sex and cycle differences in analgesia (nociception) from oxycodone in rats and related these to sex and cycle differences in brain and plasma oxycodone and metabolite levels. Since numerous opioids are CYP2D enzyme substrates and variation in CYP2D alters opioid drug levels and response, we also initiated studies to see if the sex and cycle differences observed might be due to differences in brain CYP2D activity. Across oxycodone doses, females in diestrus had higher analgesia (using tail flick latency) compared to males and females in estrus; we also demonstrated a direct effect of estrous cycle on analgesia within females. Consistent with the analgesia, females in diestrus had highest brain oxycodone levels (assessed using microdialysis) compared to males and females in estrus. Analgesia correlated with brain oxycodone, but not brain oxymorphone or noroxycodone levels, or plasma drug or metabolite levels. Propranolol (a CYP2D mechanism-based inhibitor), versus vehicle pre-treatments, increased brain oxycodone, and decreased brain oxymorphone/oxycodone drug level ratios (an in vivo CYP2D activity phenotype in the brain) in males and females in estrus, but not in females in diestrus. Brain oxymorphone/oxycodone inversely correlated with analgesia. Together, both sex and estrous cycle impact oxycodone analgesia and brain oxycodone levels, likely through regulation of brain CYP2D oxycodone metabolism. As CYP2D6 is expressed in human brain, perhaps similar sex and cycle influences also occur in humans.

Post-operative pain following cardiac implantable electronic device implantation: insights from the BRUISE CONTROL trials

AIMS

Post-operative pain following cardiac implantable electronic device (CIED) insertion is associated with patient dissatisfaction, emotional distress, and emergency department visits. We sought to identify factors associated with post-operative pain and develop a prediction score for post-operative pain.

METHODS AND RESULTS

All patients from the BRUISE CONTROL-1 and 2 trials were included in this analysis. A validated Visual Analogue Scale (VAS) was used to assess the severity of pain related to CIED implant procedures. Patients were asked to grade the most severe post-operative pain, average post-operative pain, and pain on the day of the first post-operative clinic. Multivariable regression analyses were performed to identify predictors of significant post-operative pain and to develop a pain-prediction score. A total of 1308 patients were included. Multivariable regression analysis found that the presence of post-operative clinically significant haematoma {CSH; P value < 0.001; odds ratio (OR) 3.82 [95% confidence interval (CI): 2.37-6.16]}, de novo CIED implantation [P value < 0.001; OR 1.90 (95% CI: 1.47-2.46)], female sex [P value < 0.001; OR 1.61 (95% CI: 1.22-2.12)], younger age [<65 years; P value < 0.001; OR 1.54 (95% CI: 1.14-2.10)], and lower body mass index [<20 kg/m2; P value < 0.05; OR 2.05 (95% CI: 0.98-4.28)] demonstrated strong and independent associations with increased post-operative pain. An 11-point post-operative pain prediction score was developed using the data.

CONCLUSION

Our study has identified multiple predictors of post-operative pain after CIED insertion. We have developed a prediction score for post-operative pain that can be used to identify individuals at risk of experiencing significant post-operative pain.

Let's talk about sex: Differences in drug therapy in males and females

Professor Henry Higgins in My Fair Lady said, 'Why can't a woman be more like a man?' Perhaps unintended, such narration extends to the reality of current drug development. A clear sex-gap exists in pharmaceutical research spanning from preclinical studies, clinical trials to post-marketing surveillance with a bias towards males. Consequently, women experience adverse drug reactions from approved drug products more often than men. Distinct differences in pharmaceutical response across drug classes and the lack of understanding of disease pathophysiology also exists between the sexes, often leading to suboptimal drug therapy in women. This review explores the influence of sex as a biological variable in drug delivery, pharmacokinetic response and overall efficacy in the context of pharmaceutical research and practice in the clinic. Prospective recommendations are provided to guide researchers towards the consideration of sex differences in methodologies and analyses. The promotion of disaggregating data according to sex to strengthen scientific rigour, encouraging innovation through the personalisation of medicines and adopting machine learning algorithms is vital for optimised drug development in the sexes and population health equity.

Sex differences in type and occurrence of adverse reactions to opioid analgesics: a retrospective cohort study

OBJECTIVES

Sex as a biological variable affects response to opioids. However, few reports describe the prevalence of specific adverse reactions to commonly prescribed opioids in men and women separately. A large cohort was used to investigate sex differences in type and occurrence of adverse reactions associated with use of codeine, tramadol, oxycodone and hydrocodone.

DESIGN

Retrospective cohort study.

SETTING

Participants in the Right Drug, Right Dose, Right Time (RIGHT) Study.

PARTICIPANTS

The medical records of 8457 participants in the RIGHT Study who received an opioid prescription between 1 January 2004 and 31 December 2017 were reviewed 61% women, 94% white, median age (Q1-Q3)=58 (47-66).

PRIMARY AND SECONDARY OUTCOME MEASURES

Adverse reactions including gastrointestinal, skin, psychiatric and nervous system issues were collected from the allergy section of each patient's medical record. Sex differences in the risk of adverse reactions due to prescribed opioids were modelled using logistic regression adjusted for age, body mass index, race and ethnicity.

RESULTS

From 8457 participants (of which 449 (5.3%) reported adverse reactions), more women (6.5%) than men (3.4%) reported adverse reactions to at least one opioid (OR (95% CI)=2.3 (1.8 to 2.8), p<0.001). Women were more likely to report adverse reactions to tramadol (OR (95% CI)=2.8 (1.8 to 4.4), p<0.001) and oxycodone (OR (95% CI)=2.2 (1.7 to 2.9), p<0.001). Women were more likely to report gastrointestinal (OR (95% CI)=3.1 (2.3 to 4.3), p<0.001), skin (OR (95% CI)=2.1 (1.4 to 3.3), p=0.001) and nervous system issues (OR (95% CI)=2.3 (1.3 to 4.2), p=0.004).

CONCLUSIONS

These findings support the importance of sex as a biological variable to be factored into pain management studies.

Sex- and Gender-Based Pharmacological Response to Drugs

In humans, the combination of all sex-specific genetic, epigenetic, and hormonal influences of biologic sex produces different in vivo environments for male and female cells. We dissect how these influences of sex modify the pharmacokinetics and pharmacodynamics of multiple drugs and provide examples for common drugs acting on specific organ systems. We also discuss how gender of physicians and patients may influence the therapeutic response to drugs. We aim to highlight sex as a genetic modifier of the pharmacological response to drugs, which should be considered as a necessary step toward precision medicine that will benefit men and women. SIGNIFICANCE STATEMENT: This study discusses the influences of biologic sex on the pharmacokinetics and pharmacodynamics of drugs and provides examples for common drugs acting on specific organ systems. This study also discusses how gender of physicians and patients influence the therapeutic response to drugs.

Pain in Women: A Perspective Review on a Relevant Clinical Issue that Deserves Prioritization

Introduction

Gender equity and gender medicine are opportunities not to be missed, and this Expert Group Opinion Paper on pain in women aims to review the treatment of pain conditions mainly affecting women, as well as the fundamental aspects of the different clinical response to drug treatment between the genders, and what can be done for gender-specific rehabilitation.

Methods

Perspective review.

Results

Genotypic and phenotypic differences in pain between the sexes are conditioned by anatomical, physiological, neural, hormonal, psychological, social, and cultural factors, such as the response to pharmacological treatment to control pain. The examination of these factors shows that women are affected by pain diseases more frequently and severely than men and that they report pain more frequently and with a lower pain threshold than men. Some forms of pain are inherently related to gender differences, such as pain related to the genitourinary system. However, other forms of chronic pain are seen more frequently in women than men, such as migraine, rheumatological, and musculoskeletal pain, in particular fibromyalgia.

Discussion

Research is needed into the pathophysiological basis for gender differences in the generation of acute pain and maintenance of chronic pain, including the factors that put women at higher risk for developing chronic pain. In addition, different specialties need to collaborate to develop gender-related diagnostic and therapeutic guidelines, and healthcare professionals need to upskill themselves in the appropriate management of pain using existing diagnostic tools and therapeutic options.

Confirmatory factor analysis of the International Pain Outcome questionnaire in surgery

Supplemental Digital Content is Available in the Text.

The reliability and validity of International Pain Outcome questionnaire Spanish adaptation is confirmed in a large heterogeneous sample. Factor scores can be used as a global outcome analysis tool.

Background:

Choosing perioperative suitable treatments requires reliable and valid outcome measurements. The International Pain Outcome (IPO) questionnaire has been widely used for quality improvement and research purposes within the PAIN-OUT network that has collected more than 550,000 data sets of postoperative patients in 200 hospitals worldwide. Our aim is to confirm psychometric properties of the Spanish version of the IPO questionnaire and its invariance by pain predictors.

Method:

Sample included 4014 participants within a large age range, who underwent different surgical procedures. Confirmatory factor analysis (CFA) assessed internal structure, considering invariance by sex, age, procedure, smoking, obesity, affective disorder, and chronic pain. Incremental predictive validity of factor scores on question would have liked more pain treatment and opioid requirement was also estimated with logistic binary regression.

Results:

Confirmatory factor analysis verified original structure in 3 factors measuring pain intensity and interference (F1), adverse effects (F2), and perceptions of care (F3), with good internal consistency. Multigroup CFA analysis confirmed invariance by assessed pain predictors. Good incremental predictive capacity to identify would have liked more pain treatment was achieved.

Conclusion:

Our study confirms the factor structure, supports reliability, and adds some evidence of convergent validity of the Spanish adaptation of the IPO questionnaire. The sum of scores in its main factors serves a global outcome analysis tool. Low scores in F1 and F2 with high scores in F3 would indicate optimal quality of care.

Greater Conditioned Pain Modulation Is Associated With Enhanced Morphine Analgesia in Healthy Individuals and Patients With Chronic Low Back Pain

OBJECTIVES

Conditioned pain modulation (CPM) protocols index magnitude of descending pain inhibition. This study evaluated whether the degree of CPM, controlling for CPM expectancy confounds, was associated with analgesic and subjective responses to morphine and whether chronic pain status or sex moderated these effects.

MATERIALS AND METHODS

Participants included 92 individuals with chronic low back pain and 99 healthy controls, none using daily opioid analgesics. In a cross-over design, participants attended 2 identical laboratory sessions during which they received either intravenous morphine (0.08 mg/kg) or saline placebo before undergoing evoked pain assessment. In each session, participants engaged in ischemic forearm and heat pain tasks, and a CPM protocol combining ischemic pain (conditioning stimulus) and heat pain (test stimulus). Placebo-controlled morphine outcomes were derived as differences in pain and subjective effects across drug conditions.

RESULTS

In hierarchical regressions controlling for CPM expectancies, greater placebo-condition CPM was associated with less subjective morphine unpleasantness (P=0.001) and greater morphine analgesia (P's<0.05) on both the ischemic pain task (Visual Analog Scale Pain Intensity and Unpleasantness) and heat pain task (Visual Analog Scale Pain Intensity, McGill Pain Questionnaire-Sensory, and Present Pain Intensity subscales). There was no moderation by sex or chronic low back pain status, except for the ischemic Present Pain Intensity outcome for which a significant 2-way interaction (P<0.05) was noted, with men showing a stronger positive relationship between CPM and morphine analgesia than women.

DISCUSSION

Results suggest that CPM might predict analgesic and subjective responses to opioid administration. Further evaluation of CPM as an element of precision pain medicine algorithms may be warranted.

Qualitative measurement of opioid effects on pain and dyspnea: gender difference in the sensitivity

Background

An increasing number of patients come to the operating room in use of opioid analgesics. They have different levels of tolerance to opioid effects which challenge the anesthesiologists in search of safe and effective opioid dosing perioperatively. The tested hypothesis is that simple measures introduced will allow us to measure tolerance qualitatively. Opioid effects on pain (analgesia) and dyspnea sensations (relieving effect) are tested. Patients were allocated to three groups according to pre-operative analgesics: (1) control, without any opioid analgesics, (2) weak opioid, and (3) strong opioid. Pressure pain threshold (PPT) and no-respiratory sensation period (NRSP) were measured at two points: before and 3 min after intravenous fentanyl administration.

Results

A total of 58 (43 controls, 9 weak opioids, and 6 strong opioids) patients were enrolled. PPT and NRSP, after iv 2 μg/kg ideal body weight (IBW) fentanyl, were significantly elevated in the control patients (PPT: 6.2 ± 2.1 N to 9.2 ± 3.9 N, p < 0.0001, NRSP: 17.8 ± 10.8 s to 22.8 ± 18.7 s, p < 0.005, paired t test). However, preoperative opioid use, though with tendency, did not show a significant decrease of the opioid effect. Due to an insufficient number of participants, no conclusion could be drawn. Further analysis of the data from control patients showed a significant difference between the two sexes in sensitivity to PPT and NRSP, as well as fentanyl effect on PPT.

Conclusions

Current data showed a simple method of measuring the opioid effect on two dimensions: pain and respiration. Though not able to show a qualitative measurement of tolerance formation in opioid-users, data from control patients showed females to be more sensitive to pain and dyspnea but is less sensitive to the opioid effect. Further studies are necessary to show whether these gender differences serve as clinical relevance.

Trial registration

UMIN, UMIN 000011580. Registered 27 August 2013, https://upload.umin.ac.jp/cgi-open-bin/ctr/ctr.cgi?function=brows&action=brows&type=summary&recptno=R000013352&language=J

Experimental sleep disruption attenuates morphine analgesia: findings from a randomized trial and implications for the opioid abuse epidemic

Preclinical studies demonstrate that sleep disruption diminishes morphine analgesia and modulates reward processing. We sought to translate these preclinical findings to humans by examining whether sleep disruption alters morphine's analgesic and hedonic properties. We randomized 100 healthy adults to receive morphine versus placebo after two nights of undisturbed sleep (US) and two nights of forced awakening (FA) sleep disruption. Sleep conditions were counterbalanced, separated by a two-week washout. The morning after both sleep conditions, we tested cold pressor pain tolerance before and 40-min after double-blind injection of .08 mg/kg morphine or placebo. The primary outcome was the analgesia index, calculated as the change in cold pressor hand withdrawal latency (HWL) before and after drug injection. Secondary outcomes were ratings of feeling "high," drug "liking," and negative drug effects. We found a significant sleep condition by drug interaction on the analgesia index (95% CI - 0.57, - 0.001). After US, subjects receiving morphine demonstrated significantly longer HWL compared to placebo (95% CI 0.23, 0.65), but not after FA (95% CI - 0.05, 0.38). Morphine analgesia was diminished threefold under FA, relative to US. After FA, females (95% CI - 0.88, - 0.05), but not males (95% CI - 0.23, 0.72), reported decreased subjective "high" effects compared to US. After FA, females (95% CI 0.05, 0.27), but not males (95% CI - 0.10, 0.11), administered morphine reported increased negative drug effects compared to US. These data demonstrate that sleep disruption attenuates morphine analgesia in humans and suggest that sleep disturbed males may be at greatest risk for problematic opioid use.

Drug-drug similarity measure and its applications

Drug similarities play an important role in modern biology and medicine, as they help scientists gain deep insights into drugs' therapeutic mechanisms and conduct wet labs that may significantly improve the efficiency of drug research and development. Nowadays, a number of drug-related databases have been constructed, with which many methods have been developed for computing similarities between drugs for studying associations between drugs, human diseases, proteins (drug targets) and more. In this review, firstly, we briefly introduce the publicly available drug-related databases. Secondly, based on different drug features, interaction relationships and multimodal data, we summarize similarity calculation methods in details. Then, we discuss the applications of drug similarities in various biological and medical areas. Finally, we evaluate drug similarity calculation methods with common evaluation metrics to illustrate the important roles of drug similarity measures on different applications.

Traumatic brain injury and the misuse of alcohol, opioids, and cannabis

Traumatic brain injury (TBI), most often classified as concussion, is caused by biomechanical forces to the brain resulting in short- or long-term impairment in brain function. TBI resulting from military combat, sports, violence, falls, and vehicular accidents is a major cause of long-term physical, cognitive, and psychiatric dysfunction. Psychiatric disorders associated with TBI include depression, anxiety, and substance use disorder, all having significant implications for post-TBI recovery and rehabilitation. This chapter reviews the current preclinical and clinical literature describing the bidirectional relationship between TBI and misuse of three commonly abused drugs: alcohol, opioids, and cannabis. We highlight the influence of each of these drugs on the incidence of TBI, as well as trends in their use after TBI. Furthermore, we discuss factors that may underlie post-injury substance use. Understanding the complex relationship between TBI and substance misuse will enhance the clinical treatment of individuals suffering from these two highly comorbid conditions.

Low-dose methadone for refractory chronic migraine accompanied by medication-overuse headache: a prospective cohort study

Objectives

A refractory chronic migraine (RCM) accompanied by medication-overuse headache (MOH) is an extremely disabling disease. Evidence suggests that in selected patients, chronic opioids may be a valuable therapeutic option for RCM. The aim of the present study was to evaluate the effectiveness and safety of prophylaxis with low-dose methadone (LDM) in patients affected by RCM with continuous headache and MOH.

Methods

A prospective cohort study was performed between May 2012 and November 2015 at the Headache Center and Toxicology Unit of the Careggi University Hospital. Eligible patients were treated with prophylactic LDM and followed up for 12 months. Headache exacerbations, pain intensity, use of rescue medications, and occurrence of adverse drug reactions (ADRs) were recorded.

Results

Thirty patients (24 females, median age 48 years) were enrolled. Nineteen (63%) patients dropped out, mainly because of early ADRs (n = 10), including nausea, vomiting, and constipation. At last available follow-up, LDM was associated with a significant decrease in the number of headache attacks/month (from a median of 45 (interquartile range 30–150) to 16 (5–30), p < 0.001), in pain intensity (from 8.5 (8–9) to 5 (3–6), p < 0.001), and in the number of rescue medications consumed per month (from 95 (34–240) to 15 (3–28), p < 0.001). No misuse or diversion cases were observed.

Conclusion

LDM could represent a valuable and effective option in selected patients affected by RCM with continuous headache and MOH, although the frequency of early ADRs poses major safety concerns. Randomized controlled trials are needed to confirm the efficacy and safety of LDM prophylaxis.

OPRM1, OPRK1, and COMT genetic polymorphisms associated with opioid effects on experimental pain: a randomized, double-blind, placebo-controlled study

Genetic polymorphisms have been shown to affect opioid requirement for pain relief. However, true genetic effect is often difficult to assess due to underlying pain conditions and placebo effects. The goal of this study was to understand how common polymorphisms affect opioid effects while controlling for these factors. A randomized, double-blind, placebo-controlled study was implemented to assess how opioid effects are modulated by COMT (rs6269, rs4633, rs4848, rs4680), OPRM1 (A118G), and OPRK1 (rs1051660, rs702764, rs16918875). One hundred and eight healthy subjects underwent experimental pain testing before and after morphine, butorphanol, and placebo (saline). Association analysis was performed between polymorphisms/haplotypes and opioid response, while correcting for race, gender, placebo effects, and multiple comparisons. Pressure pain was significantly associated with rs6269 and rs4633 following butorphanol. The AA genotype of rs4680 or A_T_C_A/ A_T_C_A (rs6269_rs4633_ rs4818_rs4680) diplotype of COMT, combined with the AG genotype of OPRM1 A118G, showed significantly increased pressure pain threshold from butorphanol. Opioid effects on pressure, ischemic, heat pain, and side effects were nominally associated with several SNPs and haplotypes. Effects were often present in one opioid but not the other. This indicates that these polymorphisms affect pain relief from opioids, and that their effects are opioid and pain modality specific.

Deep Reinforcement Learning for Optimal Critical Care Pain Management with Morphine using Dueling Double-Deep Q Networks

Opioids are the preferred medications for the treatment of pain in the intensive care unit. While under-treatment leads to unrelieved pain and poor clinical outcomes, excessive use of opioids puts patients at risk of experiencing multiple adverse effects. In this work, we present a sequential decision making framework for opioid dosing based on deep reinforcement learning. It provides real-time clinically interpretable dosing recommendations, personalized according to each patient's evolving pain and physiological condition. We focus on morphine, one of the most commonly prescribed opioids. To train and evaluate the model, we used retrospective data from the publicly available MIMIC-3 database. Our results demonstrate that reinforcement learning may be used to aid decision making in the intensive care setting by providing personalized pain management interventions.

Sex-Specific Pharmacotherapy for Migraine: A Narrative Review

Migraine is a common neurological disorder characterized by recurrent headache episodes that accompany sensory-motor disturbances, such as higher sensitivity to touch and light, extremity heaviness or weakness, and speech or language disabilities. Worldwide, migraine is one of the top 10 causes of disability and hence poses a huge economic burden to society. On average, migraine occurs in 12% of population but its occurrence is sexually dimorphic, as it is two to three times more prevalent in women than in men. This female to male ratio of migraine prevalence is age- and sex hormone-dependent. Advancements in understanding migraine pathogenesis have also revealed an association with both genetics and epigenetics. The severity of migraine, in terms of its attack duration, headache intensity, frequency, and occurrence of migraine-associated symptoms, has generally been reported to be greater in women. Sex differences in migraine disability and comorbidities, such as psychiatric disorders, have also been noted in some population-based studies. However, research on sex-related differences in response to migraine treatments is relatively scarce. Although a general observation is that women consume more medication than men for migraine treatment, strategies for the use of abortive and preventive medications for migraine are generally similar in both sexes. This narrative review summarizes available findings on sexually distinct responses to abortive and prophylactic pharmacotherapy of migraine. Basic experimental data and clinical findings will be presented, and potential mechanisms underlying sex-based responses will be discussed to highlight the importance and value of sex-based treatment in migraine research and practice.

Effect of Transcranial Direct Current Stimulation Combined With Patient-Controlled Intravenous Morphine Analgesia on Analgesic Use and Post-Thoracotomy Pain. A Prospective, Randomized, Double-Blind, Sham-Controlled, Proof-of-Concept Clinical Trial

Background

Transcranial direct current stimulation (tDCS) is used for various chronic pain conditions, but experience with tDCS for acute postoperative pain is limited. This study investigated the effect of tDCS vs. sham stimulation on postoperative morphine consumption and pain intensity after thoracotomy.

Methods

This is a single-center, prospective, randomized, double-blind, sham-controlled trial in lung cancer patients undergoing thoracotomy under general anesthesia. All patients received patient-controlled (PCA) intravenous morphine and intercostal nerve blocks at the end of surgery. The intervention group (a-tDCS, n = 31) received anodal tDCS over the left primary motor cortex (C3-Fp2) for 20 min at 1.2 mA, on five consecutive days; the control group (n = 31) received sham stimulation. Morphine consumption, number of analgesia demands, and pain intensity at rest, with movement and with cough were recorded at the following intervals: immediately before (T1), immediately after intervention (T2), then every hour for 4 h (Т3-Т6), then every 6 h (Т7-Т31) for 5 days. We recorded outcomes on postoperative days 1 and 5 and conducted a phone interview inquiring about chronic pain 1 year later (NCT03005548).

Results

A total of 62 patients enrolled, but tDCS was prematurely stopped in six patients. Fifty-five patients (27 a-tDCS, 28 sham) had three or more tDCS applications and were included in the analysis. Cumulative morphine dose in the first 120 h after surgery was significantly lower in the tDCS [77.00 (54.00-123.00) mg] compared to sham group [112.00 (79.97-173.35) mg, p = 0.043, Cohen's d = 0.42]. On postoperative day 5, maximum visual analog scale (VAS) pain score with cough was significantly lower in the tDCS group [29.00 (20.00-39.00) vs. 44.50 (30.00-61.75) mm, p = 0.018], and pain interference with cough was 80% lower [10.00 (0.00-30.00) vs. 50.00 (0.00-70.00), p = 0.013]. One year after surgery, there was no significant difference between groups with regard to chronic pain and analgesic use.

Conclusion

In lung cancer patients undergoing thoracotomy, three to five tDCS sessions significantly reduced cumulative postoperative morphine use, maximum VAS pain scores with cough, and pain interference with cough on postoperative day 5, but there was no obvious long-term benefit from tDCS.

Sex differences in opioid reinforcement under a fentanyl vs. food choice procedure in rats

Clinical evidence suggest that men are more sensitive than women to the abuse-related effects of mu-opioid agonists. In contrast, preclinical studies suggest the opposite sex difference. The aim of the present study was to clarify this discrepancy using a fentanyl vs. diluted Ensure^® choice procedure to assess sex differences in opioid reinforcement. Sex differences in intravenous (IV) fentanyl self-administration were examined under a fixed-ratio (FR5) schedule, a multi-day progressive-ratio (PR) schedule for behavioral economic analysis, and a concurrent (choice) schedule of fentanyl and diluted Ensure^® reinforcement in Sprague-Dawley male and female rats. The fentanyl dose-effect function under the FR5 schedule was significantly shifted upward in females compared to males. Similarly, the reinforcing effectiveness of both fentanyl (3.2 and 10 µg/kg per injection, IV) and diluted Ensure^® (18 and 56%) were greater in females than in males as assessed using behavioral economic analysis, irrespective of dose or concentration. However, under a fentanyl vs. foodchoice procedure, males chose 3.2 µg/kg per injection fentanyl injections over 18%, but not 56%, diluted Ensure^® at a higher percentage compared to females. Overall, these results suggest that the expression of sex differences in opioid reinforcement depends upon the schedule of reinforcement and that preclinical opioid vs. food choice procedures provide a translationally relevant measure (i.e., behavioral allocation) consistent with the direction of sex differences reported in the clinical literature.

Sex differences in pain and opioid mediated antinociception: Modulatory role of gonadal hormones

Sex-related differences in pain and opioids has been the focus of many researches. It is demonstrated that women experience greater clinical pain, lower pain threshold and tolerance, more sensitivity and distress to experimentally induced pain compared to men. Sex differences in response to opioid treatment revealed inconsistent results. However, the etiology of these disparities is not fully elucidated. It is, therefore, conceivable now that this literature merits to be revisited comprehensively. Possible multifaceted factors seem to be associated. These include neuroanatomical, hormonal, neuroimmunological, psychological, social and cultural aspects and comorbidities. This review aims at providing an overview of the substantial literature documenting the sex differences in pain and analgesic response to opioids from animal and human studies within the context of the modulatory effects of the aforementioned factors. A detailed and critical discussion of the cellular and molecular signaling pathways underlying the modulatory actions of gonadal hormones in the sexual dimorphism in pain processing and opioid analgesia is extensively presented. It is indicated that sexual dimorphic activation of certain brain regions contributes to differential pain sensitivity between females and males. Plausible crosstalk between sex hormones and neuroimmunological signaling pertinent to toll-like and purinergic receptors is uncovered as causal cues underlying sexually dimorphic pain and opioid analgesia. Conceivably, a thorough understanding of these factors may aid in sex-related advancement in pain therapeutic management.

An Open Trial of Morning Bright Light Treatment Among US Military Veterans with Chronic Low Back Pain: A Pilot Study

OBJECTIVE

To examine the feasibility, acceptability, and effects of a home-based morning bright light treatment on pain, mood, sleep, and circadian timing in US veterans with chronic low back pain.

DESIGN

An open treatment trial with a seven-day baseline, followed by 13 days of a one-hour morning bright light treatment self-administered at home. Pain, pain sensitivity, mood, sleep, and circadian timing were assessed before, during, and after treatment.

SETTING

Participants slept at home, with weekly study visits and home saliva collections.

PARTICIPANTS

Thirty-seven US veterans with medically verified chronic low back pain.

METHODS

Pain, mood, and sleep quality were assessed with questionnaires. Pain sensitivity was assessed using two laboratory tasks: a heat stimulus and an ischemia stimulus that gave measures of threshold and tolerance. Sleep was objectively assessed with wrist actigraphy. Circadian timing was assessed with the dim light melatonin onset.

RESULTS

Morning bright light treatment led to reduced pain intensity, pain behavior, thermal pain threshold sensitivity, post-traumatic stress disorder symptoms, and improved sleep quality (P < 0.05). Phase advances in circadian timing were associated with reductions in pain interference (r = 0.55, P < 0.05).

CONCLUSIONS

Morning bright light treatment is a feasible and acceptable treatment for US veterans with chronic low back pain. Those who undergo morning bright light treatment may show improvements in pain, pain sensitivity, and sleep. Advances in circadian timing may be one mechanism by which morning bright light reduces pain. Morning bright light treatment should be further explored as an innovative treatment for chronic pain conditions.

The impact of cuff width and biological sex on cuff preference and the perceived discomfort to blood-flow-restricted arm exercise

OBJECTIVE

To investigate the influence of cuff width, sex, and applied pressure on the perceived discomfort associated with blood flow restriction at rest and following exercise.

APPROACH

Experiment 1 (n  =  96) consisted of four sets of biceps exercise to failure with a narrow and wide cuff inflated to the same relative pressure. Experiment 2 (n  =  87) compared two wide cuffs, one of which was inflated to a relative pressure obtained from a narrow cuff. Experiment 3 (n  =  50) compared the discomfort of wide and narrow cuffs at rest. Effects are presented as median δ (95% credible interval).

MAIN RESULTS

There was no sex effect for any variable of interest. In Experiment 1, the narrow cuff resulted in less discomfort than the wide cuff (39.3 versus 42.5; median δ  -0.388 (-0.670, -0.109)). Participants also rated the narrow cuff as more preferable. Experiment 2 found that a wide cuff inflated to a narrow cuffs pressure resulted in greater discomfort than a wide cuff (44 versus 40.9; median δ: 0.420 (0.118, 0.716)). Experiment 3 found no difference between cuff widths.

SIGNIFICANCE

Blood flow restricted exercise with a narrow cuff results in less discomfort than a wider cuff inflated to the same relative pressure. This effect is not observed at rest and suggests that the wide cuff produces a differential environment compared to a narrow cuff when combined with exercise. Additionally, applying a pressure meant for a narrow cuff to a wide cuff augments the applied pressure and subsequent discomfort to blood flow restricted exercise.

Side effects from opioids used for acute pain after emergency department discharge

OBJECTIVE

Opioid side effects are common when treating chronic pain. However, the frequency of opioid side effects has rarely been examined in acute pain conditions, particularly in a post emergency department (ED) setting. The objective of this study was to evaluate the short-term incidence of opioid-induced side effects (constipation, nausea/vomiting, dizziness, drowsiness, sweating, and weakness) in patients discharged from the ED with an opioid prescription.

METHODS

This is a prospective cohort study of patients aged ≥18 years who visited the ED for an acute pain condition (≤2 weeks) and were discharged with an opioid prescription. Patients completed a 14-day diary assessing daily pain medication use and side effects.

RESULTS

We recruited 386 patients with a median age of 54 years (IQR:43-66); 50% were women. During the 2-week follow-up, 80% of patients consumed opioids. Among the patients who used opioids, 79% (95%CI:75-83) reported side effects compared to 38% (95%CI:27-49) for non-users. Adjusting for age, sex, and pain condition, patients who used opioids were more likely to report constipation (OR:7.5; 95%CI:3.1-17.9), nausea/vomiting (OR:4.1; 95%CI:1.8-9.5), dizziness (OR:5.4; 95%CI: 2.2-13.2), drowsiness (OR:4.6; 95%CI:2.5-8.7), and weakness (OR:4.2; 95%CI:1.6-11.0) compared to non-users. A dose-response trend was observed for constipation but not for the other side effects. Nausea/vomiting (OR:2.0; 95%CI:1.1-3.6) and dizziness (OR:1.9; 95%CI:1.1-3.4) were more often associated with oxycodone than with morphine.

CONCLUSION

As observed for chronic pain treatment, side effects are highly prevalent during short-term opioid treatment for acute pain. Physicians should inform patients about those side effects and should consider prescribing laxatives.

Neuronal and glial factors contributing to sex differences in opioid modulation of pain

Morphine remains one of the most widely prescribed opioids for alleviation of persistent and/or severe pain; however, multiple preclinical and clinical studies report that morphine is less efficacious in females compared to males. Morphine primarily binds to the mu opioid receptor, a prototypical G-protein coupled receptor densely localized in the midbrain periaqueductal gray. Anatomical and physiological studies conducted in the 1960s identified the periaqueductal gray, and its descending projections to the rostral ventromedial medulla and spinal cord, as an essential descending inhibitory circuit mediating opioid-based analgesia. Remarkably, the majority of studies published over the following 30 years were conducted in males with the implicit assumption that the anatomical and physiological characteristics of this descending inhibitory circuit were comparable in females; not surprisingly, this is not the case. Several factors have since been identified as contributing to the dimorphic effects of opioids, including sex differences in the neuroanatomical and neurophysiological characteristics of the descending inhibitory circuit and its modulation by gonadal steroids. Recent data also implicate sex differences in opioid metabolism and neuroimmune signaling as additional contributing factors. Here we cohesively present these lines of evidence demonstrating a neural basis for sex differences in opioid modulation of pain, with a focus on the PAG as a sexually dimorphic core of descending opioid-induced inhibition and argue for the development of sex-specific pain therapeutics.

Risk factors of opioid-induced adverse reactions in elderly male outpatients of Korea Veterans Hospital

Background

Risk factors associated with opioid-induced adverse reactions (OIARs) in the elderly population have not been well defined. The objective of this study was to determine effects of various risk factors on incidence of OIARs in male elderly patients.

Methods

A retrospective cohort study in Korea Veterans Hospital was performed. Data were analyzed in male patients aged 65 years and older who received morphine, oxycodone, or codeine. Binomial variables describing patient-related and drug-related characteristics were constructed. Associations between these variables and frequency of OIARs were determined. Odds ratio (OR) and adjusted odds ratio (AOR) were calculated from univariate and multivariable analyses, respectively. Attributable risk was obtained by (1–1/OR)*100%.

Results

Of 316 patients, 28% experienced at least one adverse event. The most common adverse events were gastrointestinal problems (n = 59) and central nerve system adverse effects (n = 20). The odds of OIARs in patients with opioid use ≥12 weeks was increased by 80% compared to those with opioid use < 12 weeks. Attributable risk of GABA analogues was 64~78% in constructed Models. Compared to codeine users, patients using morphine and oxycodone had 653 and 473% increased odds for OIARs, respectively. MME ≥ 60 mg/day had a 317% increased odds for OIARs (95% CI: 1.92–9.04) compared to MME < 60 mg/day. Opioid combination therapy had a 139% increased odds for OIARs compared to monotherapy.

Conclusions

These findings have significant implications for clinical use of opioid in elderly patients. Our study suggests that low dose short-term use will pose less risk of OIARs for the elderly, whereas concomitant use of GABA analogues, strong opioids and dual-opioid therapy may increase the risk of OIARs. Therefore, clinician should carefully monitor patients when starting opioid therapy in older population.

Impact of sex on pain and opioid analgesia: a review

Chronic pain is a debilitating condition that impacts tens of millions each year, resulting in lost wages for workers and exacting considerable costs in health care and rehabilitation. A thorough understanding of the neural mechanisms underlying pain and analgesia is critical to facilitate the development of therapeutic strategies and personalized medicine. Clinical and epidemiological studies report that women experience greater levels of pain than men and have higher rates of pain-related disorders. Studies in both rodents and humans report sex differences in the anatomical and physiologic properties of the descending antinociceptive circuit, mu opioid receptor (MOR) expression and binding, morphine metabolism, and immune system activation, all of which likely contribute to the observed sex differences in pain and opioid analgesia. Although more research is needed to elucidate the underlying mechanisms, these sex differences present potential therapeutic targets to optimize pain management strategies for both sexes.

Expectancy Effects on Conditioned Pain Modulation Are Not Influenced by Naloxone or Morphine

BACKGROUND

Recent studies suggest that participant expectations influence pain ratings during conditioned pain modulation testing. The present study extends this work by examining expectancy effects among individuals with and without chronic back pain after administration of placebo, naloxone, or morphine.

PURPOSE

This study aims to identify the influence of individual differences in expectancy on changes in heat pain ratings obtained before, during, and after a forearm ischemic pain stimulus.

METHODS

Participants with chronic low back pain (n = 88) and healthy controls (n = 100) rated heat pain experience (i.e., "test stimulus") before, during, and after exposure to ischemic pain (i.e., "conditioning stimulus"). Prior to testing, participants indicated whether they anticipated that their heat pain would increase, decrease, or remain unchanged during ischemic pain.

RESULTS

Analysis of the effects of expectancy (pain increase, decrease, or no change), drug (placebo, naloxone, or morphine), and group (back pain, healthy) on changes in heat pain revealed a significant main effect of expectancy (p = 0.001), but no other significant main effects or interactions. Follow-up analyses revealed that individuals who expected lower pain during ischemia reported significantly larger decreases in heat pain as compared with those who expected either no change (p = 0.004) or increased pain (p = 0.001).

CONCLUSIONS

The present findings confirm that expectancy is an important contributor to conditioned pain modulation effects, and therefore significant caution is needed when interpreting findings that do not account for this individual difference. Opioid mechanisms do not appear to be involved in these expectancy effects.

Do Resting Plasma β-Endorphin Levels Predict Responses to Opioid Analgesics?

OBJECTIVES

Clinically feasible predictors of opioid analgesic responses for use in precision pain medicine protocols are needed. This study evaluated whether resting plasma β-endorphin (BE) levels predicted responses to an opioid analgesic, and whether chronic pain status or sex moderated these effects.

METHODS

Participants included 73 individuals with chronic low back pain (CLBP) and 88 pain-free controls, all using no daily opioid analgesics. Participants attended 2 identical laboratory sessions during which they received either intravenous morphine (0.08 mg/kg) or saline placebo, with blood samples obtained before drug administration to assay resting plasma BE levels. Once peak drug activity was achieved in each session, participants engaged in an ischemic forearm pain task (ISC) and a heat pain task. Morphine analgesic effects were derived reflecting the difference in pain outcomes between placebo and morphine conditions.

RESULTS

In hierarchical regressions, significant Type (CLBP vs. control)×BE interactions (Ps<0.05) were noted for morphine effects on ISC tolerance, ISC intratask pain ratings, and thermal VAS unpleasantness ratings. These interactions derived primarily from associations between higher BE levels and smaller morphine effects restricted to the CLBP subgroup. All other BE-related effects, including sex interactions, for predicting morphine analgesia failed to reach statistical significance.

DISCUSSION

BE was a predictor of morphine analgesia for only 3 out of 9 outcomes examined, with these effects moderated by chronic pain status but not sex. On the whole, results do not suggest that resting plasma BE levels are likely to be a clinically useful predictor of opioid analgesic responses.

Intrathecal Trialing of Continuous Infusion Combination Therapy With Hydromorphone and Bupivacaine in Failed Back Surgery Patients

OBJECTIVES

Intrathecal (IT) trial is a prognostic interventional pain management procedure employed to determine the potential success of treating intractable pain with an implantable infusion device system. There is a dearth of data regarding trials with continuous infusion of combination therapy (e.g. opioid combined with local anesthetic). The objective of the this study was to determine the overall outcomes of continuous infusion IT trials and factors influencing long-term success of IT therapy in patients with chronic intractable pain post-laminectomy.

MATERIALS AND METHODS

This is a retrospective analysis of all patients with lumbar failed back surgery syndrome (FBSS) who were trialed with a combination of hydromorphone and bupivacaine with a temporary externalized IT catheter from March 2007 to June 2014.

RESULTS

From a cohort of 62 patients fulfilling the inclusion criteria, 54 (87.10%) patients had successful IT trials. No significant differences were found between successful and failed trial patients with regards to age, sex, pre-trial pain numeric rating scale scores, pre-trial morphine equivalent daily dose, or trial dosages. Significant positive correlations were found between pretrial oral opioid intake and end of trial hydromorphone dose and hydromorphone dose escalation at 12 months and 24 months.

CONCLUSIONS

Patients with refractory low back pain due to FBSS who underwent successful combination IT trial with hydromorphone and bupivacaine infused through a temporary IT catheter had significantly improved pain intensity scores following permanent implant. Higher pre-trial MEDD was correlated with higher trial and post-implant opioid doses and higher rates of opioid dose escalation post-implant.

Psychosocial factors predict opioid analgesia through endogenous opioid function

Use of opioid analgesics for management of chronic nonmalignant pain has become common, yet there are presently no well-validated predictors of optimal opioid analgesic efficacy. We examined whether psychosocial factors (eg, depressive symptoms) predicted changes in spontaneous low back pain after administration of opioid analgesics, and whether endogenous opioid (EO) function mediated these relationships. Participants with chronic low back pain but who were not chronic opioid users (N = 89) underwent assessment of low back pain intensity pre- and post-drug in 3 (counterbalanced) conditions: (1) placebo, (2) intravenous naloxone, and (3) intravenous morphine. Comparison of placebo condition changes in back pain intensity to those under naloxone and morphine provided indexes of EO function and opioid analgesic responses, respectively. Results showed that (1) most psychosocial variables were related significantly and positively to morphine analgesic responses for low back pain, (2) depressive symptoms, trait anxiety, pain catastrophizing, and pain disability were related negatively to EO function, and (3) EO function was related negatively to morphine analgesic responses for low back pain. Bootstrapped mediation analyses showed that links between morphine analgesic responses and depressive symptoms, trait anxiety, pain catastrophizing, and perceived disability were partially mediated by EO function. Results suggest that psychosocial factors predict elevated analgesic responses to opioid-based medications, and may serve as markers to identify individuals who benefit most from opioid therapy. Results also suggest that people with greater depressive symptoms, trait anxiety, pain catastrophizing, and perceived disability may have deficits in EO function, which may predict enhanced response to opioid analgesics.

Sex differences in innate immunity and its impact on opioid pharmacology

Morphine has been and continues to be one of the most potent and widely used drugs for the treatment of pain. Clinical and animal models investigating sex differences in pain and analgesia demonstrate that morphine is a more potent analgesic in males than in females. In addition to binding to the neuronal μ-opioid receptor, morphine binds to the innate immune receptor toll-like receptor 4 (TLR4), located on glial cells. Activation of glial TLR4 initiates a neuroinflammatory response that directly opposes morphine analgesia. Females of many species have a more active immune system than males; however, few studies have investigated glial cells as a potential mechanism driving sexually dimorphic responses to morphine. This Mini-Review illustrates the involvement of glial cells in key processes underlying observed sex differences in morphine analgesia and suggests that targeting glia may improve current treatment strategies for pain. © 2016 Wiley Periodicals, Inc.

The burden of chronic pain after major head and neck tumor therapy

Introduction:

Little is known about the burden of chronic pain after major head and neck tumors’ therapy. In this study, we aimed to estimate the prevalence of chronic pain, explore the factors associated with the presence of chronic pain, and assess the consequences of chronic pain on the patients’ quality of life.

Methodology:

This was a cross-sectional survey among patients who had completed their therapy (e.g., surgery, radiotherapy, and chemotherapy) for major head and neck (larynx, nasopharynx, oropharynx, hypopharynx, oral cavity, tongue, and sinuses) tumors after at least 3 months. We collected relevant demographic and clinical data and administered the Brief Pain Inventory-Short Form, Neuropathic Pain Questionnaire-Short Form, and Pain Catastrophizing Scale questionnaires. Possible risk factors were explored using a classification tree model.

Results:

A total of 102 patients (59 men, 42 women) were enrolled in this study between 3 and 72 months after tumor treatment. 30% of the patients reported having chronic pain after their major head and neck tumors’ therapy. The average pain score in the last 24-hr was 3.4 (standard deviation = 2.7). The prevalence of patients with chronic pain was higher (42%) among those who had surgery. Factors associated with chronic pain were female sex, older age, surgery, advanced cancer stage, and radiotherapy. Patients who reported having chronic pain also reported having a lower quality of life manifested by impairments in general activity, mood, walking ability, normal work, and sleeping. Patients who reported having chronic pain had higher Pain Catastrophizing Scale scores.

Conclusion:

Our study highlighted the high burden of chronic pain after therapy for major head and neck tumors. We identified demographic and clinical factors that are associated with the presence of chronic pain. Further studies are required to better understand the risk factors to implement strategies to prevent, alleviate, and treat chronic pain associated with major head and neck tumor therapies.

Acupuncture-induced changes of pressure pain threshold are mediated by segmental inhibition--a randomized controlled trial

Our aim was to distinguish between spinal and supraspinal mechanisms in the intact nervous system by comparing homosegmental and heterosegmental effects of electroacupuncture (EA) and manual acupuncture (MA) on sensory perception in healthy volunteers by means of quantitative sensory testing. Seventy-two healthy volunteers were randomly assigned to receive either MA or EA at SP 6, SP 9, GB 39, and ST 36 at the left leg or relaxed for 30 minutes (control group [CG]). Blinded examiners assessed 13 sensory modalities (thermal and mechanical detection and pain thresholds) at the upper arms and lower legs before and after intervention by means of a standardized quantitative sensory testing battery. Change scores of all 13 sensory thresholds were compared between groups. The main outcome measure was the change score of the pressure pain threshold (PPT). There were no baseline differences between groups. Pressure pain threshold change scores at the lower left leg, in the same segment as the needling site, differed significantly (P = 0.008) between the EA (median: 103.01 kPa) and CG groups (median: 0.00 kPa) but not between the MA (median: 0.00 kPa) and CG groups. No further significant change score differences were found between one of the acupuncture groups and the CG. The PPT can be changed by EA. The PPT increase was confined to the segment of needling, which indicates that it is mainly mediated by segmental inhibition in the spinal cord. This underscores the importance of segmental needling and electrical stimulation in clinical practice.

Sex and Gender Differences in Central Nervous System-Related Disorders

There are important sex differences in the brain that seem to arise from biology as well as psychosocial influences. Sex differences in several aspects of human behavior and cognition have been reported. Gonadal sex steroids or genes found on sex chromosomes influence sex differences in neuroanatomy, neurochemistry and neuronal structure, and connectivity. There has been some resistance to accept that sex differences in the human brain exist and have biological relevance; however, a few years ago, it has been recommended by the USA National Institute of Mental Health to incorporate sex as a variable in experimental and clinical neurological and psychiatric studies. We here review the clinical literature on sex differences in pain and neurological and psychiatric diseases, with the aim to further stimulate interest in sexual dimorphisms in the brain and brain diseases, possibly encouraging more research in the field of the implications of sex differences for treating these conditions.