Determination of the Effective Dose of Pregabalin on Human Experimental Pain Using the Sequential Up-Down Method

Norharmane potentiated anxiolytic- and antidepressant-like responses induced by imipramine and citalopram: an isobologram analysis

β-carboline compounds display a therapeutic property for treating depression and anxiety behaviors. Imipramine and citalopram play an important role in the modulation of anxiety and depression behaviors. We investigated the effects of norharmane, imipramine, and citalopram on anxiety- and depression-like effects and their interactions. Elevated plus maze and forced swimming test were used for the assessment of anxiety- and depression-like behaviors in male mice. The results revealed that intraperitoneal (i.p.) administration of norharmane (10 mg/kg) increased percentage of open arm time (%OAT) in the elevated plus maze test and decreased immobility time in the forced swimming test, proposing anxiolytic- and antidepressant-like effects. Injection of imipramine (5 mg/kg; i.p.) enhanced %OAT and decreased immobility time, suggesting anxiolytic- and antidepressant-like effects. Moreover, norharmane potentiated the anxiolytic- and antidepressant-like responses induced by imipramine by increasing %OAT and decreasing immobility time. The results revealed additive anxiolytic- and antidepressant-like effects between norharmane and imipramine in mice. Alone, the administration of citalopram (5 mg/kg; i.p.) enhanced %OAT and reduced immobility time, causing anxiolytic- and antidepressant-like effects. When citalopram and norharmane were coinjected, norharmane augmented the anxiolytic- and antidepressant-like effects induced by citalopram by increasing %OAT and reducing immobility time. These results indicated additive anxiolytic- and antidepressant-like effects between norharmane and antidepressant drugs such as imipramine and citalopram on the modulation of anxiety and depression processes in mice.

Effectiveness and Adverse Events of Gabapentinoids as Analgesics for Patients with Burn Injuries: A Systematic Review with Meta-Analysis and Trial Sequential Analysis

(1) Background: Pain after a burn injury is difficult to endure, and emerging studies aim to ascertain the effects of gabapentin and pregabalin as non-opioid treatment options. (2) Methods: We searched for randomised controlled trials (RCTs) in six databases. The risk of bias was assessed using the RoB 2.0 tool. We performed meta-analysis and trial sequential analysis and used the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) methodology for judging the certainty of evidence (CoE). (3) Results: Five RCTs were included. Compared with placebo, gabapentinoids significantly decreased the pain intensity within 24 h (mean difference (MD) = -1.06, 95% confidence interval (CI): -1.47--0.65) and from 72 h to 9 days (MD = -0.82, 95% CI: -1.16--0.48), but not after 3 weeks (MD = -0.44, 95% CI: -1.31-0.42). Opioid consumption (mg/day) was reduced within 24 h (MD = -13.34, 95% CI: -22.16--4.52) and from 72 h to 9 days (MD = -7.87, 95% CI: -14.82--0.91). Increased risks of drowsiness (risk ratio (RR) = 3.255, 95% CI: 1.135-9.335) and dizziness (RR = 3.034, 95% CI: 1.006-9.147) were observed, but sensitivity analysis using the Bayesian method showed no increased risk. All endpoints were judged as low to very low CoE. (4) Conclusions: Gabapentinoids offer modest analgesic benefits as a component of multimodal pain management for burn injuries of less than 3 weeks. The adverse effects should be carefully monitored. Large-scale RCTs are warranted for the reinforcement of CoE in clinical use.

Effect of Pregabalin on the Median Effective Plasma Concentration of Intravenous Alfentanil in Capsaicin-Induced Pain

OBJECTIVE

To apply the sequential up-down method to a human experimental pain model in order to examine the opioid-sparing effect of oral pregabalin on intravenous alfentanil.

DESIGN

Double-blind, randomized, crossover.

SETTING

Academic university medical center.

SUBJECTS

Thirty-one healthy males.

METHODS

The median effective plasma concentration of intravenous alfentanil was determined under two conditions: alfentanil alone (phase I) and alfentanil+ pregabalin (300 mg orally) (phase II). The alfentanil plasma level (after a computer-controlled infusion) producing a success criterion (at least 30% intradermal capsaicin-induced pain reduction compared with placebo) was used to determine higher or lower doses for each sequential subject. The median dose producing a success criterion and its confidence interval were determined.

RESULTS

On the basis of the t test for a difference across phase and regression coefficients across groups, there was no opioid-sparing effect of pregabalin on alfentanil. Four subjects in phase I and five subjects in phase II did not complete the study. Two in phase I were technical failures, with the rest in both phases stopped because of side effects. Of the subjects who completed the study, six of 19 subjects in phase I and 11 of 12 subjects in phase II reported side effects.

CONCLUSIONS

When the intradermal capsaicin-induced pain model was used in healthy volunteers, oral pregabalin had no opioid-sparing effects on intravenous alfentanil. This experimental model may be useful in studying analgesic interactions.

Human surrogate models of central sensitization: A critical review and practical guide

Background

As in other fields of medicine, development of new medications for management of neuropathic pain has been difficult since preclinical rodent models do not necessarily translate to the clinics. Aside from ongoing pain with burning or shock‐like qualities, neuropathic pain is often characterized by pain hypersensitivity (hyperalgesia and allodynia), most often towards mechanical stimuli, reflecting sensitization of neural transmission.

Data treatment

We therefore performed a systematic literature review (PubMed‐Medline, Cochrane, WoS, ClinicalTrials) and semi‐quantitative meta‐analysis of human pain models that aim to induce central sensitization, and generate hyperalgesia surrounding a real or simulated injury.

Results

From an initial set of 1569 reports, we identified and analysed 269 studies using more than a dozen human models of sensitization. Five of these models (intradermal or topical capsaicin, low‐ or high‐frequency electrical stimulation, thermode‐induced heat‐injury) were found to reliably induce secondary hyperalgesia to pinprick and have been implemented in multiple laboratories. The ability of these models to induce dynamic mechanical allodynia was however substantially lower. The proportion of subjects who developed hypersensitivity was rarely provided, giving rise to significant reporting bias. In four of these models pharmacological profiles allowed to verify similarity to some clinical conditions, and therefore may inform basic research for new drug development.

Conclusions

While there is no single “optimal” model of central sensitization, the range of validated and easy‐to‐use procedures in humans should be able to inform preclinical researchers on helpful potential biomarkers, thereby narrowing the translation gap between basic and clinical data.

Significance

Being able to mimic aspects of pathological pain directly in humans has a huge potential to understand pathophysiology and provide animal research with translatable biomarkers for drug development. One group of human surrogate models has proven to have excellent predictive validity: they respond to clinically active medications and do not respond to clinically inactive medications, including some that worked in animals but failed in the clinics. They should therefore inform basic research for new drug development.

Patient phenotyping in clinical trials of chronic pain treatments: IMMPACT recommendations

There is tremendous interpatient variability in the response to analgesic therapy (even for efficacious treatments), which can be the source of great frustration in clinical practice. This has led to calls for “precision medicine” or personalized pain therapeutics (ie, empirically based algorithms that determine the optimal treatments, or treatment combinations, for individual patients) that would presumably improve both the clinical care of patients with pain and the success rates for putative analgesic drugs in phase 2 and 3 clinical trials. However, before implementing this approach, the characteristics of individual patients or subgroups of patients that increase or decrease the response to a specific treatment need to be identified. The challenge is to identify the measurable phenotypic characteristics of patients that are most predictive of individual variation in analgesic treatment outcomes, and the measurement tools that are best suited to evaluate these characteristics. In this article, we present evidence on the most promising of these phenotypic characteristics for use in future research, including psychosocial factors, symptom characteristics, sleep patterns, responses to noxious stimulation, endogenous pain-modulatory processes, and response to pharmacologic challenge. We provide evidence-based recommendations for core phenotyping domains and recommend measures of each domain.

A data science approach to the selection of most informative readouts of the human intradermal capsaicin pain model to assess pregabalin effects

Persistent and, in particular, neuropathic pain is a major healthcare problem with still insufficient pharmacological treatment options. This triggered research activities aimed at finding analgesics with a novel mechanism of action. Results of these efforts will need to pass through the phases of drug development, in which experimental human pain models are established components e.g. implemented as chemical hyperalgesia induced by capsaicin. We aimed at ranking the various readouts of a human capsaicin-based pain model with respect to the most relevant information about the effects of a potential reference analgesic. In a placebo-controlled, randomized cross-over study, seven different pain-related readouts were acquired in 16 healthy individuals before and after oral administration of 300 mg pregabalin. The sizes of the effect on pain induced by intradermal injection of capsaicin were quantified by calculating Cohen's d. While in four of the seven pain-related parameters, pregabalin provided a small effect judged by values of Cohen's d exceeding 0.2, an item categorization technique implemented as computed ABC analysis identified the pain intensities in the area of secondary hyperalgesia and of allodynia as the most suitable parameters to quantify the analgesic effects of pregabalin. Results of this study provide further support for the ability of the intradermal capsaicin pain model to show analgesic effects of pregabalin. Results can serve as a basis for the designs of studies where the inclusion of this particular pain model and pregabalin is planned.

Prophylactic Pregabalin to Decrease Pain During Medication Abortion: A Randomized Controlled Trial

OBJECTIVE

To evaluate whether prophylactic pregabalin reduces pain experienced with medication abortion.

METHODS

We conducted a randomized, double-blind, placebo-controlled trial of women initiating medication abortion with mifepristone and buccal misoprostol up to 70 days of gestation. Participants were randomized to 300 mg oral pregabalin or a placebo immediately before misoprostol. The primary outcome was maximum pain on an 11-point numerical rating scale, reported using real-time electronic surveys over 72 hours. Secondary outcomes included pain at each time point, ibuprofen and narcotic use, side effects, and satisfaction. We estimated that 110 women would be required to have 80% power to detect a difference in pain of 1.3 points.

RESULTS

Between June 2015 and October 2016, 241 women were screened and 110 were randomized (56 pregabalin, 54 placebo). Three were lost to follow-up. The primary outcome of mean maximum pain in the pregabalin group was 5.0±2.6 vs 5.5±2.2 in the placebo group (P=.32). Excluding medication taken before the study capsule, ibuprofen was used by 64% (35/55) of the pregabalin group vs 87% (45/52) placebo (P<.01). Narcotics were used by 29% (16/55) of the pregabalin group vs 50% (26/52) placebo (P<.03). More dizziness (P<.001), sleepiness (P<.04), and blurred vision (P<.05) occurred in the pregabalin group. Satisfaction scores for the analgesic regimen were higher in the pregabalin group (very satisfied: 47% vs 22%; P=.006).

CONCLUSION

Compared with placebo, 300 mg pregabalin coadministered with misoprostol during medication abortion did not significantly decrease maximum pain scores. Women who received pregabalin were less likely to require any ibuprofen or narcotic and were more likely to report higher satisfaction with analgesia, despite an increase in dizziness, sleepiness, and blurred vision.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, NCT02782169.

Patient phenotyping in clinical trials of chronic pain treatments: IMMPACT recommendations

There is tremendous interpatient variability in the response to analgesic therapy (even for efficacious treatments), which can be the source of great frustration in clinical practice. This has led to calls for "precision medicine" or personalized pain therapeutics (ie, empirically based algorithms that determine the optimal treatments, or treatment combinations, for individual patients) that would presumably improve both the clinical care of patients with pain and the success rates for putative analgesic drugs in phase 2 and 3 clinical trials. However, before implementing this approach, the characteristics of individual patients or subgroups of patients that increase or decrease the response to a specific treatment need to be identified. The challenge is to identify the measurable phenotypic characteristics of patients that are most predictive of individual variation in analgesic treatment outcomes, and the measurement tools that are best suited to evaluate these characteristics. In this article, we present evidence on the most promising of these phenotypic characteristics for use in future research, including psychosocial factors, symptom characteristics, sleep patterns, responses to noxious stimulation, endogenous pain-modulatory processes, and response to pharmacologic challenge. We provide evidence-based recommendations for core phenotyping domains and recommend measures of each domain.

A Randomized, Double-Blind, Placebo-Controlled, Crossover Study of the T-Type Calcium Channel Blocker ABT-639 in an Intradermal Capsaicin Experimental Pain Model in Healthy Adults

OBJECTIVE

This randomized, double-blind, placebo-controlled, crossover trial evaluated the pharmacodynamic effects of a single 100-mg dose of ABT-639, a peripherally active, selective T-type Ca_v3.2 channel blocker, with the intradermal capsaicin pain model using pregabalin 300 mg as a positive control.

SUBJECTS

Healthy adult males (aged 21 to 55 years) were randomly assigned to receive single oral doses of ABT-639, pregabalin, and placebo.

METHODS

Serial measurements for area (cm²) of hyperalgesia, allodynia, and flare response were performed over a 20-minute period after each capsaicin injection at 1 and 4 hours post-dose. Capsaicin injections were administered in different arms as determined by random assignment. Serial measurements for spontaneous pain and elicited pain were performed over a 60-minute period at 1 and 4 hours post-dose using a 100-mm visual analog scale. Standard safety evaluations were performed.

RESULTS

Nineteen participants were randomized and included in the analysis. No significant differences were observed between ABT-639 and placebo in spontaneous pain, elicited pain, and areas of allodynia, hyperalgesia, and flare after intradermal capsaicin injection at 1 and 4 hours post-dose. In contrast, pregabalin demonstrated significant reductions in spontaneous pain at 1 and 4 hours post-dose, and elicited pain and areas of allodynia and hyperalgesia at 4 hours post-dose compared with placebo. ABT-639 demonstrated acceptable safety and tolerability; somnolence and euphoric mood were the most commonly reported adverse events.

CONCLUSIONS

These data indicate that a single 100-mg dose of ABT-639 had no effect on experimental pain induced by intradermal capsaicin injection.

Pregabalin reduces opioid consumption and improves outcome in chronic pain patients undergoing total knee arthroplasty

INTRODUCTION

Recently, multimodal pain control has been used to manage postoperative pain in patients undergoing total knee arthroplasty (TKA). This approach combines numerous modalities, such as opioids, nonsteroidal anti-inflammatory drugs, local anesthetics, and acetaminophen, in an effort to reduce overall opioid consumption and also to provide better pain control. Gabapentinoids are a class of drugs that have been used as part of multimodal approach, and may be effective in patients who are previous users of chronic pain medication. The hypothesis of this study was that the addition of pregabalin reduces opioid consumption and/or improves pain after TKA, even in patients who are previous users of chronic pain medications.

METHODS

Using a prospectively collected database, 262 consecutive patients undergoing primary TKA between December 2011 and April 2012 were identified who received multimodal analgesia after surgery that included pregabalin. Using the same database, these patients were compared with 268 patients undergoing TKA from January to December 2010 who also received multimodal analgesia but were not given pregabalin. The clinical records of these patients were reviewed in detail to determine the incidence and nature of postoperative complications, opioid consumption, and visual analog scale (VAS) pain scores.

RESULTS

The incidence of respiratory, renal, and hemodynamic complications was significantly lower in the patients who received pregabalin. Gastrointestinal complications, which included nausea, were not significantly different between the groups. Patients receiving pregabalin had a lower average opioid consumption, and their minimum and maximum levels of opioid consumption were also reduced. Previous users of chronic pain medications had higher VAS scores but the same opioid consumption compared with those who were not previous users of chronic pain medications. No difference was seen in the maximum VAS scores between patients who received pregabalin and those who did not.

CONCLUSION

Pregabalin in the context of multimodal pain management may be associated with reduced opioid consumption and other medical complications in patients undergoing TKA, including previous users of chronic pain medications.