Effects of azapropazone on pain-related brain activity in human subjects

[Effect of pre-administered flurbiprofen axetil on the EC50 of propofol during anesthesia in unstimulated patients: a randomized clinical trial]

BACKGROUND AND OBJECTIVES

Preoperative use of flurbiprofen axetil (FA) is extensively adopted to modulate the effects of analgesia. However, the relationship between FA and sedation agents remains unclear. In this study, we aimed to investigate the effects of different doses of FA on the median Effective Concentration (EC50) of propofol.

METHODS

Ninety-six patients (ASA I or II, aged 18-65 years) were randomly assigned into one of four groups in a 1:1:1:1 ratio. Group A (control group) received 10 mL of Intralipid, and groups B, C and D received 0.5 mg.kg^-1, 0.75 mg.kg^-1 and 1 mg.kg^-1 of FA, respectively, 10 minutes before induction. The depth of anesthesia was measured by the Bispectral Index (BIS). The "up-and-down" method was used to calculate the EC50 of propofol. During the equilibration period, if BIS ≤ 50 (or BIS > 50), the next patient would receive a 0.5 μg.mL^-1-lower (or-higher) propofol Target-Controlled Infusion (TCI) concentration. The hemodynamic data were recorded at baseline, 10 minutes after FA administration, after induction, after intubation, and 15 minutes after intubation.

RESULTS

The EC50 of propofol was lower in Group C (2.32 μg.mL^-1, 95% Confidence Interval [95% CI] 1.85-2.75) and D (2.39 μg.mL^-1, 95% CI 1.91-2.67) than in Group A (2.96 μg.mL^-1, 95% CI 2.55-3.33) (p = 0.023, p = 0.048, respectively). There were no significant differences in the EC50 between Group B (2.53 μg.mL^-1, 95% CI 2.33-2.71) and Group A (p ˃ 0.05). There were no significant differences in Heart Rate (HR) among groups A, B and C. The HR was significantly lower in Group D than in Group A after intubation (66 ± 6 vs. 80 ± 10 bpm, p < 0.01) and 15 minutes after intubation (61 ± 4 vs. 70 ± 8 bpm, p < 0.01). There were no significant differences among the four groups in Mean Arterial Pressure (MAP) at any time point. The MAP of the four groups was significantly lower after induction, after intubation, and 15 minutes after intubation than at baseline (p < 0.05).

CONCLUSION

High-dose FA (0.75 mg.kg^-1 or 1 mg.kg^-1) reduces the EC50 of propofol, and 1 mg.kg^-1 FA reduces the HR for adequate anesthesia in unstimulated patients. Although this result should be investigated in cases of surgical stimulation, we suggest that FA pre-administration may reduce the propofol requirement when the depth of anesthesia is measured by BIS.

Electroencephalography and analgesics

To assess centrally mediated analgesic mechanisms in clinical trials with pain patients, objective standardized methods such as electroencephalography (EEG) has many advantages. The aim of this review is to provide the reader with an overview of present findings in analgesics assessed with spontaneous EEG and evoked brain potentials (EPs) in humans. Furthermore, EEG methodologies will be discussed with respect to translation from animals to humans and future perspectives in predicting analgesic efficacy. We searched PubMed with MeSH terms 'analgesics', 'electroencephalography' and 'evoked potentials' for relevant articles. Combined with a search in their reference lists 15 articles on spontaneous EEG and 55 papers on EPs were identified. Overall, opioids produced increased activity in the delta band in the spontaneous EEG, but increases in higher frequency bands were also seen. The EP amplitudes decreased in the majority of studies. Anticonvulsants used as analgesics showed inconsistent results. The N-methyl-D-aspartate receptor antagonist ketamine showed an increase in the theta band in spontaneous EEG and decreases in EP amplitudes. Tricyclic antidepressants increased the activity in the delta, theta and beta bands in the spontaneous EEG while EPs were inconsistently affected. Weak analgesics were mainly investigated with EPs and a decrease in amplitudes was generally observed. This review reveals that both spontaneous EEG and EPs are widely used as biomarkers for analgesic drug effects. Methodological differences are common and a more uniform approach will further enhance the value of such biomarkers for drug development and prediction of treatment response in individual patients.

A novel approach to pharmaco-EEG for investigating analgesics: assessment of spectral indices in single-sweep evoked brain potentials

AIMS

To compare results from analysis of averaged and single-sweep evoked brain potentials (EPs) by visual inspection and spectral analysis in order to identify an objective measure for the analgesic effect of buprenorphine and fentanyl.

METHODS

Twenty-two healthy males were included in a randomized study to assess the changes in EPs after 110 sweeps of painful electrical stimulation to the median nerve following treatment with buprenorphine, fentanyl or placebo patches. Bone pressure, cutaneous heat and electrical pain ratings were assessed. EPs and pain assessments were obtained before drug administration, 24, 48, 72 and 144 h after beginning of treatment. Features from EPs were extracted by three different approaches: (i) visual inspection of amplitude and latency of the main peaks in the average EPs, (ii) spectral distribution of the average EPs and (iii) spectral distribution of the EPs from single-sweeps.

RESULTS

Visual inspection revealed no difference between active treatments and placebo (all P > 0.05). Spectral distribution of the averaged potentials showed a decrease in the beta (12-32 Hz) band for fentanyl (P = 0.036), which however did not correlate with pain ratings. Spectral distribution in the single-sweep EPs revealed significant increases in the theta, alpha and beta bands for buprenorphine (all P < 0.05) as well as theta band increase for fentanyl (P = 0.05). For buprenorphine, beta band activity correlated with bone pressure and cutaneous heat pain (both P = 0.04, r = 0.90).

CONCLUSION

In conclusion single-sweep spectral band analysis increases the information on the response of the brain to opioids and may be used to identify the response to analgesics.

Chemo-somatosensory evoked potentials: a sensitive tool to assess conditioned pain modulation?

Abstract Background: Chemo-somatosensory evoked potentials (CSSEPs) elicited by chemical stimulation (CO₂ gas) of the nasal mucosa have been shown to be sensitive enough to pick up even weak analgesic effects. With the present study we wanted to investigate whether CSSEPs are also a sensitive tool to capture endogenous pain inhibitory mechanisms elicited by conditioned pain modulation (CPM; where a first conditioning stimulus reduces the sensitivity for a second test stimulus) with a conditioning stimulus of rather low noxious load.

METHODS

Seventeen healthy participants were tested for CPM effects (conditioning stimulus: tonic heat pain with intensities around the pain threshold induced via a thermode; test stimulus: chemonasal stimulation (73% and 78% CO₂)) on CSSEPs and on self-report ratings.

RESULTS

We found significant CPM effects in the CSSEPS, with reduced amplitudes and prolonged latencies at several electroencephalogram (EEG) recording positions when using the lower CO₂ concentration (73% CO₂). In contrast to the visible inhibitory effects on the CSSEPs, subjective ratings of the test stimulus did not reflect CPM action.

DISCUSSION

The experimental pain model using CO₂ stimuli to elicit CSSEPs proved to be sensitive enough to capture weak CPM effects elicited by a conditioning stimulus of rather low noxious load. The usage of such mild noxious conditioning stimuli-in contrast to stimuli of higher noxious load (e.g., cold pressor test)-has the advantage that the activation of other types of pain inhibitory mechanisms in parallel (like attentional distraction, stress-induced analgesia) can be avoided.

Tonic stimulation of the pharyngeal mucosa causes pain and a reversible increase of inflammatory mediators

Objective and design

To develop a model of the inflammatory component of non-infectious sore throat using tonic stimulation and quantification of inflammatory mediators in pharyngeal lavage fluid.

Material or subjects

Forty-five healthy volunteers.

Treatment

Cold dry air.

Method

Tonic stimulation of the pharynx was achieved using a constant stream of cold dry air to the back of the throat. Following optimization of stimulation conditions (phase 1), pharyngeal pain, irritation, and swallowing discomfort were assessed using visual analog scales, and the concentration of inflammatory markers were measured in pharyngeal lavage fluid (phase 2).

Results

Optimum conditions for tonic pharyngeal stimulation were cold dry air at 12 °C, relative humidity 20 %, at a flow rate of 12 L/min for 15 min. Analysis of pharyngeal lavage fluid collected 5 min after stimulation showed significant increases in prostaglandin E₂ (P = 0.018), thromboxane B₂ (P < 0.001), and substance P (P < 0.001), but no increase in peptidoleukotriene. When the stimulus was removed, the level of inflammatory markers in pharyngeal lavage fluid returned to baseline by 30 min post-stimulation. These objective measures mirrored subjective pain ratings.

Conclusions

Tonic stimulation of the pharyngeal mucosa with cold dry air causes pain and an increase of inflammatory mediators which are reversible.

Electronic supplementary material

The online version of this article (doi:10.1007/s00011-013-0663-7) contains supplementary material, which is available to authorized users.

Caffeine accelerates absorption and enhances the analgesic effect of acetaminophen

The aim of this study was to determine the analgesic effect of acetaminophen compared to a combination of both caffeine and acetaminophen or caffeine alone using tonic and phasic pain stimulation. Twenty-four subjects were treated orally with 1000 mg acetaminophen, 130 mg caffeine, and a combination of both in a 4-way crossover, double-blind, placebo-controlled study. Pharmacokinetics and analgesic effects were assessed by means of an experimental pain model based on pain-related cortical potentials after phasic stimulation of the nasal mucosa with CO(2) and based on pain ratings after tonic stimulation with dry air. Analgesic effects of acetaminophen and acetaminophen plus caffeine but not caffeine alone caused a significant reduction of pain-related cortical potentials beginning 30 minutes after medication. The combination demonstrated an enhanced effect throughout the observation time up to 3 hours. Caffeine accelerated acetaminophen absorption, indicated by enhanced early AUCs. Significant analgesic effects of the combination on tonic pain ratings were found throughout the observation time as compared to acetaminophen and placebo. In this study, caffeine enhanced and prolonged the analgesic activity of acetaminophen.

Sex differentiated responses to intranasal trigeminal stimuli

The aim of the study was to address sex-related hemispheric differences in trigeminal event-related potentials while controlling for the subjects' olfactory sensitivity. Event-related potentials to lateralized stimulation using the trigeminal stimulant CO(2) were recorded in 28 healthy young subjects (16 women). There was no sex-related difference in olfactory sensitivity. Results indicated a sex-differentiated response to trigeminally induced pain. Women were found to have generally higher amplitudes and shorter latencies of the late positive component than men. Moreover, men and women exhibited different hemispheric activations in that women expressed shorter latencies over the left hemisphere than men. The pronounced sex-related difference of the late positive component suggests a cognitive/emotional impact on the processing of intranasal pain as indicated by others.

The influence of stimulus duration on the reliability of pain ratings after nociceptive stimulation of the nasal mucosa with CO2

Nociceptive stimuli consisting of short pulses of gaseous CO(2) applied to the nasal mucosa were investigated in 12 healthy volunteers (six males, six females) with respect to trial-to-trial variability. A statistical rather than a psychophysical approach was employed, focusing on test-retest reliability. According to a randomized, volunteer-blind crossover design, two repeated measurements for each of four stimulus durations (200, 400, 800 and 1600 ms) were performed on eight different days. During measurements, a total of 80 stimuli of 16 concentrations of CO(2) (40-70% v/v in 2% steps) was applied with an interstimulus interval at 30 s. The interday variability of the pain ratings was lowest at a stimulus duration of 400 ms and highest at 200 ms. The results show that stimulus duration may affect the statistical outcome of studies on pain, and should be considered when setting up an experimental pain model.

Pain in the trigeminal system: irritation of the nasal mucosa using short- and long-lasting stimuli

The paper describes methods which allow intranasal irritation using short- and long-lasting painful stimuli in humans. Short-lasting pain is induced by gaseous CO(2), while long-lasting pain is induced by a stream of dry air. Both models have been explored regarding their major determinants, e.g. stimulus duration, stimulus intensity, or repeated stimulation. Short-lasting, non-inflammatory pain stimuli seem to provide specific indicators of A(delta)-fiber function, while responses to long-lasting, inflammatory pain appear to be indicative of C-fiber function. Responses to both types of painful stimuli are modulated by analgesic drugs. As these well-investigated models allow the detailed and precise analysis of modulatory effects on intranasal nociception, they appear to be suited for the investigation of subtle changes of intranasal irritation, e.g. induced by environmental agents.

Peripheral and central nervous changes in patients with rheumatoid arthritis in response to repetitive painful stimulation

It has been observed that patients with rheumatoid arthritis (RA) respond differently to repetitive painful stimulation. The present study investigated whether this is related to the peripheral or central nervous nociceptive system. EEG-derived potentials and the negative mucosal potential (NMP) from the respiratory epithelium were recorded in response to painful intranasal stimulation with gaseous CO(2). Differences between groups (12 RA patients, 12 controls) were found when stimuli were presented at short intervals. While the NMP did not differ between groups, patients had larger cortical responses to the first stimuli of a series of painful stimuli. This may indicate that in RA central nervous changes of nociceptive processing are present.

Assessment of intranasal trigeminal function

Intranasal trigeminal function is more and more understood as an integral part of human chemosensory perception. Sensations like burning, stinging, warmth, coolness, or itching are produced by almost all odorants so that they can be perceived by anosmics. Electrophysiological responses to trigeminal stimuli allow the specific assessment of trigeminally mediated information at different levels of processing including the periphery or the cortex. Information regarding the localization of these processes can be derived from magnetoencephalographic recordings or functional imaging data. When using these techniques in combination with psychophysical measures, it seems to be possible to specifically describe how and where the processing of irritation takes place, how it may interact with olfactory mediated sensations, and how it is modulated, e.g. by environmental influences or analgesic drugs.

Population pharmacokinetics of fast release oral diclofenac in healthy volunteers: relation to pharmacodynamics in an experimental pain model

PURPOSE

Population pharmacokinetics of a fast release diclofenac were assessed with special focus on pharmacodynamic implications.

METHODS

In a double blind four-way crossover study, 20 healthy volunteers received orally 50 and 100 mg diclofenac-Na effervescent ("fast-release NSAID"), 50 mg diclofenac tablets ("control"), or placebo. Population pharmacokinetics of the fast release diclofenac were assessed using a nonlinear mixed effects modeling approach (NON-MEM). Analgesic effects were investigated by means of an experimental pain model based on both pain-ratings and cortical evoked potentials after specific stimulation of nasal nociceptors with short pulses of gaseous CO2.

RESULTS

Pharmacokinetics of fast release diclofenac were best described by a two-compartment population model, with an estimated terminal half-life of 1.2 hours. Pharmacokinetics of diclofenac tablets were highly variable and a population pharmacokinetic model could not be obtained. As an indication of an early onset of analgesic effects, 100 mg fast release diclofenac but not the tablets significantly reduced the amplitudes of pain-related evoked potentials at 30 min after administration.

CONCLUSIONS

Earlier drug absorption and lower pharmacokinetic variability of the fast-release formulation are likely to be preserved in a population.