Effects of flurbiprofen enantiomers on pain-related chemo-somatosensory evoked potentials in human subjects

Comparison of bromazepam and ibuprofen influence on tooth pulp-evoked potentials in humans

Introduction/Objective Somatosensory evoked potentials are a neurophysiological tool for testing the effects of drugs in humans and animals. The aim of this study was to estimate the way that bromazepam and ibuprofen had on tooth pulp-evoked potentials (TPEPs) after non-painful stimuli, as well as to detect possible differences in this activity. Methods Sixty young healthy subjects were included in the study. They were arranged into three groups: ibuprofen, bromazepam and placebo. To record TPEPs response, dental pulp was electrically stimulated through intact enamel with non-painful stimuli. For stimulation and registration, we used Xltek Protektor 32 system, software EPWorks, version 5.0. The experiment consisted of two testing sessions. Five recordings were performed in each session. The first test session was before, and the second was 45 minutes after administration of a single dose of the ibuprofen (400 mg), bromazepam (1.5 mg) or placebo. Results The results of the present study exhibit that both ibuprofen and bromazepam significantly increased all the latencies; ibuprofen decreased amplitudes of all the waves except the first one (p < 0.05), and bromazepam decreased amplitudes of all the waves except the first one (p < 0.05); placebo did not modified TPEPs waves (p > 0.05). Additionally, there were no significant differences in influence on TPEPs between bromazepam and ibuprofen (p > 0.05). Conclusion Our study showed that both bromazepam and ibuprofen had the same influence on TPEPs after non-painful stimuli. That indicates that anxiolytic dose of bromazepam affects neurotransmission in the same manner as non-opioid analgesics ibuprofen.

Druggable Targets in Endocannabinoid Signaling

Cannabis and cannabinoid-based extracts have long been utilized for their perceived therapeutic value, and support for the legalization of cannabis for medicinal purposes continues to increase worldwide. Since the discovery of Δ⁹-tetrahydrocannabinol (THC) as the primary psychoactive component of cannabis over 50 years ago, substantial effort has been directed toward detection of endogenous mediators of cannabinoid activity. The discovery of anandamide and 2-arachidonoylglycerol as two endogenous lipid mediators of cannabinoid-like effects (endocannabinoids) has inspired exponential growth in our understanding of this essential pathway, as well as the pathological conditions that result from dysregulated endocannabinoid signaling. This review examines current knowledge of the endocannabinoid system including metabolic enzymes involved in biosynthesis and degradation and their receptors, and evaluates potential druggable targets for therapeutic intervention.

Endocannabinoid and Prostanoid Crosstalk in Pain

Interfering with endocannabinoid (eCB) metabolism to increase their levels is a proven anti-nociception strategy. However, because the eCB and prostanoid systems are intertwined, interfering with eCB metabolism will affect the prostanoid system and inversely. Key to this connection is the production of the cyclooxygenase (COX) substrate arachidonic acid upon eCB hydrolysis as well as the ability of COX to metabolize the eCBs anandamide (AEA) and 2-arachidonoylglycerol (2-AG) into prostaglandin-ethanolamides (PG-EA) and prostaglandin-glycerol esters (PG-G), respectively. Recent studies shed light on the role of PG-Gs and PG-EAs in nociception and inflammation. Here, we discuss the role of these complex systems in nociception and new opportunities to alleviate pain by interacting with them.

R-Flurbiprofen Traps Prostaglandins within Cells by Inhibition of Multidrug Resistance-Associated Protein-4

R-flurbiprofen is the non-COX-inhibiting enantiomer of flurbiprofen and is not converted to S-flurbiprofen in human cells. Nevertheless, it reduces extracellular prostaglandin E₂ (PGE₂) in cancer or immune cell cultures and human extracellular fluid. Here, we show that R-flurbiprofen acts through a dual mechanism: (i) it inhibits the translocation of cPLA_2α to the plasma membrane and thereby curtails the availability of arachidonic acid and (ii) R-flurbiprofen traps PGE₂ inside of the cells by inhibiting multidrug resistance–associated protein 4 (MRP4, ABCC4), which acts as an outward transporter for prostaglandins. Consequently, the effects of R-flurbiprofen were mimicked by RNAi-mediated knockdown of MRP4. Our data show a novel mechanism by which R-flurbiprofen reduces extracellular PGs at physiological concentrations, particularly in cancers with high levels of MRP4, but the mechanism may also contribute to its anti-inflammatory and immune-modulating properties and suggests that it reduces PGs in a site- and context-dependent manner.

R-flurbiprofen attenuates experimental autoimmune encephalomyelitis in mice

R-flurbiprofen is the non-cyclooxygenase inhibiting R-enantiomer of the non-steroidal anti-inflammatory drug flurbiprofen, which was assessed as a remedy for Alzheimer's disease. Because of its anti-inflammatory, endocannabinoid-modulating and antioxidative properties, combined with low toxicity, the present study assessed R-flurbiprofen in experimental autoimmune encephalomyelitis (EAE) models of multiple sclerosis in mice. Oral R-flurbiprofen prevented and attenuated primary progressive EAE in C57BL6/J mice and relapsing-remitting EAE in SJL mice, even if the treatment was initiated on or after the first flare of the disease. R-flurbiprofen reduced immune cell infiltration and microglia activation and inflammation in the spinal cord, brain and optic nerve and attenuated myelin destruction and EAE-evoked hyperalgesia. R-flurbiprofen treatment increased CD4(+)CD25(+)FoxP3(+) regulatory T cells, CTLA4(+) inhibitory T cells and interleukin-10, whereas the EAE-evoked upregulation of pro-inflammatory genes in the spinal cord was strongly reduced. The effects were associated with an increase of plasma and cortical endocannabinoids but decreased spinal prostaglandins, the latter likely due to R to S inversion. The promising results suggest potential efficacy of R-flurbiprofen in human MS, and its low toxicity may justify a clinical trial.

The Potential of Inhibitors of Endocannabinoid Metabolism for Drug Development: A Critical Review

The endocannabinoids anandamide and 2-arachidonoylglycerol are metabolised by both hydrolytic enzymes (primarily fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MGL)) and oxygenating enzymes (e.g. cyclooxygenase-2, COX-2). In the present article, the in vivo data for compounds inhibiting endocannabinoid metabolism have been reviewed, focussing on inflammation and pain. Potential reasons for the failure of an FAAH inhibitor in a clinical trial in patients with osteoarthritic pain are discussed. It is concluded that there is a continued potential for compounds inhibiting endocannabinoid metabolism in terms of drug development, but that it is wise not to be unrealistic in terms of expectations of success.

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.

Controlling 2-arachidonoylglycerol metabolism as an anti-inflammatory strategy

The endocannabinoid system is implicated in, and regulates, several physiological processes, ranging from food intake and energy balance to pain and inflammation. 2-Arachidonoylglycerol (2-AG) is a full agonist at the cannabinoid receptors which classically mediate its effects. The activity of this bioactive lipid is dependent on its endogenous levels, which are tightly controlled by several hydrolases, monoacylglycerol lipase and α/β-hydrolase domain 6 and 12. Moreover, 2-AG is also a substrate of cyclooxygenase-2, and this reaction leads to the formation of prostaglandin glycerol esters, the effects of which remain to be fully elucidated. In this review we discuss the multiple mechanisms by which 2-AG controls inflammation and the therapeutic potential of 2-AG metabolism inhibitors.

Direct resolution and quantitative analysis of flurbiprofen enantiomers using microcrystalline cellulose triacetate plates: applications to the enantiomeric purity control and optical isomer determination in widely consumed drugs

Flurbiprofen enantiomers have very different pharmacological properties, since the (S)-(+) form has a much higher anti-inflammatory activity than the (R)-(-) isomer, the latter being responsible for very undesirable side effects, such as gastrointestinal irritation. Based on the different biological properties of flurbiprofen enantiomers, the development of chiral chromatographic methods for the control of the enantiomeric purity is a very important topic. In this study the separation of flurbiprofen enantiomers was achieved using for the first time noncommercial MCTA layers with polyvinyl alcohol as binder, which gives to these plates a mechanical stability equivalent to that of marketed ones. Baseline resolution (α = 1.31; RS = 2.0) was obtained with ethanol-acetic acid solution (pH 3.0 ± 0.1; 60:40, v/v) as eluent and a migration distance of about 14.5 cm. Under these experimental conditions, the thin-layer chromatography determination of the enantiomeric purity of the pharmacologically active (S)-(+)-flurbiprofen in the presence of 1% of the undesired (R)-(-) form was demonstrated. Moreover, the quantitative analysis of flurbiprofen enantiomers was achieved, obtaining quantification limits and detection limits of 50 and 25 ng of each enantiomer applied to the plate, respectively. The method was succesfully applied to the enantiomer determination in widely consumed drugs, obtaining results consistent with the flurbiprofen content declared in the drug facts.

(R)-Profens are substrate-selective inhibitors of endocannabinoid oxygenation by COX-2

Cyclooxygenase-2 (COX-2) catalyzes the oxygenation of arachidonic acid and the endocannabinoids 2-arachidonoylglycerol and arachidonoylethanolamide. Evaluation of a series of COX-2 inhibitors revealed that many weak competitive inhibitors of arachidonic acid oxygenation are potent inhibitors of endocannabinoid oxygenation. (R) enantiomers of ibuprofen, naproxen and flurbiprofen, which are considered to be inactive as COX-2 inhibitors, are potent 'substrate-selective inhibitors' of endocannabinoid oxygenation. Crystal structures of the COX-2–(R)-naproxen and COX-2–(R)-flurbiprofen complexes verified this unexpected binding and defined the orientation of the (R) enantiomers relative to (S) enantiomers. (R)-Profens selectively inhibited endocannabinoid oxygenation by lipopolysaccharide-stimulated dorsal root ganglion (DRG) cells. Substrate-selective inhibition provides new tools for investigating the role of COX-2 in endocannabinoid oxygenation and a possible explanation for the ability of (R)-profens to maintain endocannabinoid tone in models of neuropathic pain.

Enantioselective pharmacokinetics of ketoprofen in piglets: the significance of neonatal age

Following intravenous dose of 6mg/kg racemic ketoprofen, the chiral pharmacokinetics of ketoprofen was investigated in eight piglets aged 6 and 21days old. S-ketoprofen predominated over R-ketoprofen in plasma of the piglets in both age groups. The volumes of distribution of S-ketoprofen for the 6- and 21-day-old piglets were 241.7 (211.3-276.5) mL/kg and 155.0 (138.7-173.1) mL/kg, respectively, while the corresponding parameters for R-ketoprofen were 289.2 (250.3-334.2) mL/kg and 193.0 (168.7-220.8) mL/kg. The clearances of R-ketoprofen [948.4 (768.0-1171.2) mL/h/kg and 425 (319.1-566.0) mL/h/kg for the 6- and 21-day-old piglets, respectively] were significantly higher compared to the clearances of S-ketoprofen [57.3 (46.6-70.4) mL/h/kg and 33.8 (27.0-42.2) mL/h/kg for 6- and 21-day-old piglets, respectively]. The elimination half-life of S-ketoprofen was 3.4h for both age groups, while the elimination half-life of R-ketoprofen was 0.2h for the 6-day-old and 0.4h for the 21-day-old piglets. The clearances of both R- and S-ketoprofen were significantly higher in the 6-day-old piglets compared to when they were 21 days old. Furthermore, the volumes of distribution were larger in the youngest age group.

Ketoprofen in piglets: enantioselective pharmacokinetics, pharmacodynamics and PK/PD modelling

The chiral pharmacokinetics and pharmacodynamics of ketoprofen were investigated in a placebo-controlled study in piglets after intramuscular administration of 6 mg/kg racemic ketoprofen. The absorption half-lives of both enantiomers were short, and S-ketoprofen predominated over R-ketoprofen in plasma. A kaolin-induced inflammation model was used to evaluate the anti-inflammatory, antipyretic and analgesic effects of ketoprofen. Skin temperatures increased after the kaolin injection, but the effect of ketoprofen was small. No significant antipyretic effects could be detected, but body temperatures tended to be lower in the ketoprofen-treated piglets. Mechanical nociceptive threshold testing was used to evaluate the analgesic effects. The piglets in the ketoprofen-treated group had significantly higher mechanical nociceptive thresholds compared to the piglets in the placebo group for 12-24 h following the treatment. Pharmacokinetic/pharmacodynamic modelling of the results from the mechanical nociceptive threshold testing gave a median IC(50) for S-ketoprofen of 26.7 μg/mL and an IC(50) for R-ketoprofen of 1.6 μg/mL. This indicates that R-ketoprofen is a more potent analgesic than S-ketoprofen in piglets. Estimated ED(50) for racemic ketoprofen was 2.5 mg/kg.

R-flurbiprofen reduces neuropathic pain in rodents by restoring endogenous cannabinoids

Background

R-flurbiprofen, one of the enantiomers of flurbiprofen racemate, is inactive with respect to cyclooxygenase inhibition, but shows analgesic properties without relevant toxicity. Its mode of action is still unclear.

Methodology/Principal Findings

We show that R-flurbiprofen reduces glutamate release in the dorsal horn of the spinal cord evoked by sciatic nerve injury and thereby alleviates pain in sciatic nerve injury models of neuropathic pain in rats and mice. This is mediated by restoring the balance of endocannabinoids (eCB), which is disturbed following peripheral nerve injury in the DRGs, spinal cord and forebrain. The imbalance results from transcriptional adaptations of fatty acid amide hydrolase (FAAH) and NAPE-phospholipase D, i.e. the major enzymes involved in anandamide metabolism and synthesis, respectively. R-flurbiprofen inhibits FAAH activity and normalizes NAPE-PLD expression. As a consequence, R-Flurbiprofen improves endogenous cannabinoid mediated effects, indicated by the reduction of glutamate release, increased activity of the anti-inflammatory transcription factor PPARγ and attenuation of microglia activation. Antinociceptive effects are lost by combined inhibition of CB1 and CB2 receptors and partially abolished in CB1 receptor deficient mice. R-flurbiprofen does however not cause changes of core body temperature which is a typical indicator of central effects of cannabinoid-1 receptor agonists.

Conclusion

Our results suggest that R-flurbiprofen improves the endogenous mechanisms to regain stability after axonal injury and to fend off chronic neuropathic pain by modulating the endocannabinoid system and thus constitutes an attractive, novel therapeutic agent in the treatment of chronic, intractable pain.

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.

Induction of apoptosis by R-flurbiprofen in human colon carcinoma cells: involvement of p53

R-flurbiprofen, a non cyclooxygenase inhibiting non-steroidal anti-inflammatory drug (NSAID), has been found to inhibit tumor growth in various animal models. In vitro experiments have shown that this effect is based on the induction of a cell cycle block and apoptosis. Cell cycle inhibition has been explained by activation of the c-Jun-N-terminal kinase (JNK) and downregulation of cyclin D1 expression. However, the molecular mechanism leading to apoptosis is unknown. Here, we show that treatment of the human colon carcinoma cell line HCT116 with different concentrations of R-flurbiprofen leads to an accumulation of p53 protein which is accompanied by an increase in phosphorylated p53 at serine 15. Mutation of serine 15 to alanine by site directed mutagenesis and overexpression of the mutated p53 gene in HCT116 cells, revealed that these cells are significantly less sensitive to apoptosis induced by R-flurbiprofen than pcDNA control cells, as measured by PARP-cleavage and flow cytometry. By contrast, no difference was detected between HCT116p53ser15ala cells and HCT116 pcDNA cells with respect to induction of a cell cycle block after R-flurbiprofen treatment. Moreover, in nude mice HCT116p53ser15ala overexpressing xenografts were significantly less sensitive to R-flurbiprofen than HCT116 pcDNA control xenografts. In conclusion, we were able to show that induction of apoptosis in HCT116 cells after R-flurbiprofen treatment is at least partly dependent on the tumor suppressor gene p53 and that mutation of p53 at serine 15 impairs the apoptotic potency of R-flurbiprofen.

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.

Rationale and feasibility of chemoprovention of hepatocellular carcinoma by cyclooxygenase-2 inhibitors

Hepatocellular carcinoma (HCC) is a growing health problem worldwide. The limited treatment and poor prognosis of this disease emphasizes the importance of developing effective prevention, including chemoprevention. Improvement in early diagnosis of HCC and regular screen of individuals with increased risk for HCC provide the possibility of effective chemoprevention for HCC in the future. Hepatocarcinogenesis is best described as a continuity of regeneration, proliferation, unregulated hyperplasia, dysplasia, and malignant transformation. Uncontrolled proliferation of hepatocytes clearly plays a key role in hepatocarcinogenesis. Overexpression of cyclooxygenase-2 (COX-2) has been associated with tumorigenesis of colon cancer. Selective COX-2 inhibitors possess potent suppression on the growth of colon cancer. Overexpression of COX-2 has also recently been demonstrated in patients with HCC, especially in nontumorous tissue with cirrhosis and well-differentiated tumorous tissue. In vitro studies have revealed that both NS-398, a selective COX-2 inhibitor, and sulindac, an analog of nonsteroidal anti-inflammatory drugs, effectively inhibit growth of human hepatoma cell lines, which is mediated by a decreased rate of cell proliferation. Although further in vivo studies are required in animal models to confirm these findings and define optimal doses for future clinical trials in human subjects, these findings provide a rationale for the use of COX-2 inhibitors as HCC chemoprevention.

Early clinical trials of chemopreventive and biologic agents: Designs, populations, and endpoints

The optimal design for initial clinical trials of chemopreventive agents for cancer has not been determined. A single design is unlikely to be the model for chemoprevention of cancer, even for prevention of a single subtype of cancer, because of the heterogeneity of drugs under investigation and the variety of biologic effects being targeted. Factors that are important in designing initial clinical trials include the proposed mechanisms of drug action, the ability and types of assays available to detect that activity or pharmacodynamic effect, and the extent of prior clinical experience. In this article, we present a discussion of the factors to be considered in initial activity studies, followed by a specific example of early clinical assessment of a noncytotoxic agent (R-flurbiprofen, E-7869) as a potential chemopreventive agent for prostate cancer.

Clinical Pharmacokinetics of Dexketoprofen

Dexketoprofen trometamol is a water-soluble salt of the dextrorotatory enantiomer of the nonsteroidal anti-inflammatory drug (NSAID) ketoprofen. Racemic ketoprofen is used as an analgesic and an anti-inflammatory agent, and is one of the most potent in vitro inhibitors of prostaglandin synthesis. This effect is due to the (S)-(+)-enantiomer (dexketoprofen), while the (R)-(-)-enantiomer is devoid of such activity. The racemic ketoprofen exhibits little stereoselectivity in its pharmacokinetics. Relative bioavailability of oral dexketoprofen (12.5 and 25mg, respectively) is similar to that of oral racemic ketoprofen (25 and 50mg, respectively), as measured in all cases by the area under the concentration-time curve values for (S)-(+)-ketoprofen. Dexketoprofen trometamol, given as a tablet, is rapidly absorbed, with a time to maximum plasma concentration (tmax) of between 0.25 and 0.75 hours, whereas the tmax for the (S)-(+)-enantiomer after the racemic drug, administered as tablets or capsules prepared with the free acid, is between 0.5 and 3 hours. The drug does not accumulate significantly when administered as 25mg of free acid 3 times daily. The profile of absorption is changed when dexketoprofen is ingested with food, reducing both the rate of absorption (tmax) and the maximal plasma concentration. Dexketoprofen is strongly bound to plasma proteins, particularly albumin. The disposition of ketoprofen in synovial fluid does not appear to be stereoselective. Dexketoprofen trometamol is not involved in the accumulation of xenobiotics in fat tissues. It is eliminated following extensive biotransformation to inactive glucuroconjugated metabolites. No (R)-(-)-ketoprofen is found in the urine after administration of dexketoprofen, confirming the absence of bioinversion of the (S)-(+)-enantiomer in humans. Conjugates are excreted in urine, and virtually no drug is eliminated unchanged. The analgesic efficacy of the oral pure (S)-(+)-enantiomer is roughly similar to that observed after double dosages of the racemic compound. At doses above 7mg, dexketoprofen was significantly superior to placebo in patients with moderate to severe pain. A dose-response relationship between 12.5 and 25mg could be seen in the time-effects curves, the superiority of the 25mg dose being more a result of an extended duration of action than of an increase in peak analgesic effect. A plateau in the analgesic activity of dexketoprofen trometamol at the 25mg dose is suggested. The time to onset of pain relief appeared to be shorter in patients treated with dexketoprofen trometamol. The drug was well tolerated.

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.

Inhibition of noxious stimulus-induced spinal prostaglandin E2 release by flurbiprofen enantiomers: a microdialysis study

Peripheral noxious stimuli have been shown to induce prostaglandin (PG) E2 release at the site of inflammation and in the spinal cord. The antiinflammatory and antinociceptive effects of cyclooxygenase-inhibiting drugs are thought to depend on the inhibition of PG synthesis. R-Flurbiprofen, however, does not inhibit cyclooxygenase activity in vitro but still produces antinociceptive effects. To find out whether R-flurbiprofen acts via inhibition of spinal PG release, concentrations of PGE2 and flurbiprofen in spinal cord tissue were assessed by microdialysis. The catheter was transversally implanted through the dorsal horns of the spinal cord at level L4. R- and S-flurbiprofen (9 and 27 mg kg(-1), respectively) were administered intravenously 10-15 min before subcutaneous injection of formalin into the dorsal surface of one hindpaw. Flurbiprofen was rapidly distributed into the spinal cord with maximal concentrations after 30-45 min. Baseline PGE2 dialysate concentrations were 100.6 +/- 6.4 pg ml(-1) (mean +/- SEM). After formalin injection they rose about threefold with a maximum of 299.4 +/- 68.4 pg ml(-1) at 7.5 min. After approximately 1 h PGE2 levels returned to baseline. Both flurbiprofen enantiomers completely prevented the formalin-induced increase of spinal PGE2 release and reduced PGE2 concentrations below basal levels. S- and R-flurbiprofen at 9 mg kg(-1) produced a minimum of 15.8 +/- 5.2 and 27.7 +/- 14.9 pg ml(-1), respectively, and 27 mg kg(-1) S- and R-flurbiprofen resulted in 11.7 +/- 1.7 and 9.3 +/- 4.7 pg ml(-1), respectively. PGE2 levels remained at the minimum up to the end of the observation period at 5 h. When 27 mg kg(-1) R-flurbiprofen was injected intravenously without subsequent formalin challenge, baseline immunoreactive PGE2 concentrations were not affected. S-Flurbiprofen (27 mg kg(-1)), however, led to a moderate reduction (approximately 40%). The data suggest that antinociception produced by R-flurbiprofen is mediated at least in part by inhibition of stimulated spinal PGE2 release and support the current view that increased spinal PGE2 release significantly contributes to nociceptive processing.

Enantiospecific pharmacokinetics and pharmacodynamics of ketoprofen in sheep

Pharmacokinetic and pharmacodynamic parameters were established for the enantiomers of the 2-arylpropionic acid (APA) nonsteroidal anti-inflammatory drug (NSAID), ketoprofen (KTP). Each enantiomer was administered separately (1.5 mg/kg) and in a racemic mixture (3 mg/kg) intravenously (i.v.) to a group of eight sheep in a four-way, four-period cross-over study using a tissue cage model of inflammation. Plasma disposition of each KTP enantiomer was similar following separate administration of the pure compounds compared to administration of the racemic mixture. S(+)KTP volume of distribution (Vd(area)) was higher and clearance (ClB) faster than those of R(-)KTP. S(+) and R(-)KTP achieved relatively low concentrations in exudate and transudate. Unidirectional limited chiral inversion of R(-) to S(+)KTP was demonstrated. After R(-)KTP administration S(+)KTP was detected in plasma, but not in either exudate or transudate. Pharmacokinetic/pharmacodynamic (PK/PD) modelling of the data could not be undertaken following R(-)KTP administration because of chiral inversion to S(+)KTP, but the pharmacodynamic parameters, calculated maximum effect (Emax), concentration producing 50% effect (EC50), Hill's coefficient (N), rate constant of elimination of drug effect from the compartment (KeO) and mean equilibration half-life (t1/2KeO) were determined for S(+)KTP after administration of the racemic mixture as well as the pure compound.

Pain treatment in multimorbid patients, the older population and other high-risk groups. The clinical challenge of reducing toxicity

The prevalence of pain is high in multimorbid patients and they can experience a multitude of painful conditions. The changes in physiology and homeostasis associated with multimorbidity and increasing age and the immature metabolism of neonates all increase the risk of toxicity from analgesics. Altered pharmacokinetics and metabolism influence drug pharmacodynamics and therapeutic windows. Imbalances in local homeostatic mechanisms increase local toxicity. The gastrointestinal organs and the kidney have a major role in the absorption, metabolism and excretion of analgesics and changes in their function predispose individuals to adverse effects. Knowledge of such compromise should influence the choice of analgesic, the administration regimen and the mode of application. The mainstay of chronic pain treatment are 3 classes of drugs: nonsteroidal anti-inflammatory drugs (NSAIDs), opioids and a host of so-called adjuvant drugs, which are used to enhance the analgesic action of the classic analgesics. In each class a wide range of drugs are available, that differ in pharmacokinetic and pharmacodynamic characteristics. These differences can be exploited to either increase analgesic efficacy and reduce toxicity, or to minimise the interference of pain therapy with daily life. Clinically important differences in analgesic and toxic effects between drugs in each analgesic class will be discussed in this article from the perspective of reducing adverse effects. New knowledge concerning the mechanism of action of analgesics and their metabolites is making the specific selection of NSAIDs and opioids to reduce adverse effects in multimorbid, chronic pain patients possible.

Analgesic efficacy and safety of (R)- ketoprofen in postoperative dental pain

This double-blind, randomized, parallel-group study compared the analgesic efficacy and safety of single doses of (R)- ketoprofen 25 mg and 100 mg to that of acetaminophen 1,000 mg and placebo in 177 patients experiencing moderate to severe pain after surgical removal of their impacted third molars. Both (R)- ketoprofen 100 mg and acetaminophen 1,000 mg were significantly (P < 0.05) more efficacious than placebo for all summary analgesic measures. Other than a more rapid analgesic onset (45 minutes versus 60 minutes) for acetaminophen 1,000 mg, (R)- ketoprofen 100 mg and acetaminophen 1,000 mg were statistically equivalent to each other. The 25 mg dose of (R)- ketoprofen appeared to approach the analgesic threshold dose, being numerically but not statistically superior to placebo for all summary measures. There were no serious adverse events observed in this study, with the overall incidence of side effects being somewhat less in the (R)- ketoprofen groups than in the acetaminophen 1,000 mg group. (R)- Ketoprofen possesses analgesic activity and an acceptable side-effect profile in the oral surgery pain model.

Preclinical enantioselective pharmacology of (R)- and (S)- ketorolac

Many of the nonsteroidal anti-inflammatory drugs (NSAIDs) are marketed as racemic mixtures, composed of (R)- and (S)- enantiomers. Racemic NSAIDs are potent cyclooxygenase (COX) inhibitors only through the action of the (S)- enantiomers, as the (R)- enantiomers do not exhibit COX inhibition. However, the (R)- enantiomer of ketoprofen exhibits potent analgesic activity and minimal ulcerogenic potential. To extend these observations, we examined the (R)- and (S)- enantiomers of RS- ketorolac, (S)- ketorolac exhibited potent COX1 and COX2 enzyme inhibition, whereas (R)- ketorolac was > 100-fold less active on both COX subtypes. Both enantiomers did not affect norepinephrine or serotonin uptake sites, and nitric oxidase or lipoxygenase activities, nor did they demonstrate any affinity for opioid receptors (mu, delta, or kappa). In experimental models, (S)- ketorolac exhibited about 10-fold greater activity than (R)- ketorolac in the murine phenylquinone writhing model. In this model, morphine sulfate was effective at much lower doses, however, and neither (R)- nor (S)- ketorolac showed any morphine-sparing effect. In the rat gait test for analgesia in the foot paw after injection of brewers yeast suspension, neither (R)- nor (S)- ketorolac affected paw volume. However, both provoked changes in gait scores, the (S)- enantiomer being 30-fold more potent than the (R)- enantiomer. A similar reduction was observed with respect to ulcerogenic potential, measured by direct microscopic changes after test conclusion. These findings suggest that (R)- ketorolac may possess analgesic activity that is independent of COX inhibition and may be associated with reduced ulcerogenic potential compared to effects exhibited by (S)- ketorolac.

Pharmacological importance of stereochemical resolution of enantiomeric drugs

Drug enantiomers have identical properties in an achiral environment, but should be considered as different chemical compounds. This is because they often differ considerably in potency, pharmacological activity and pharmacokinetic profile, since the modules with which they interact in biological systems are also optically active. Within biological systems, the metabolism of one isomer may be via a different pathway or occur at a different rate from that of the other isomer. Preferential binding of one isomer to plasma proteins may cause differences in circulating free drug and hence alter concentrations at active sites. Interactions of both isomers may differ at the active sites through which pharmacological action is mediated. Actions and levels of activity of the stereoisomers in vivo may also differ. All the pharmacological activity may reside in a single enantiomer, whereas several possibilities exist for the other enantiomer-- it may be inactive, have a qualitatively different effect, an antagonistic effect or produce greater toxicity. Two isomers may have nearly identical qualitative pharmacological activity, qualitatively similar pharmacological activity but quantitatively different potency, or qualitatively different pharmacological activity. To avoid adverse effects and optimise the therapeutic value of enantiomeric drugs, it is necessary that methods for the resolution of racemates be evolved and devolved to determine isomeric purity, establish the effectiveness of isomers of the drug, and detect the presence of an enantiomer with lower therapeutic activity and undesirable adverse effects. Even if a drug is given as a pure enantiomer, methods to discriminate between enantiomers are required because racemisation can occur both in vitro and in vivo. Methods developed for resolution of drug enantiomers should facilitate routine testing of single isomers and their metabolites, studies of pharmacological, toxicological and clinical effectiveness, routine analysis of racemates, pure enantiomers or intermediates in manufacturing processes, and investigation of the potential for inversion of an enantiopure drug substance during the early stages of drug development and therapeutic drug monitoring.

New insights into the site and mode of antinociceptive action of flurbiprofen enantiomers

The S-enantiomer of flurbiprofen has been shown to have both antiinflammatory and antinociceptive effects, whereas R-flurbiprofen is antinociceptive but not antiinflammatory. Importantly, only S-flurbiprofen inhibited prostaglandin biosynthesis in vitro at therapeutic concentrations. R-flurbiprofen did not undergo significant chiral inversion to S-flurbiprofen in rats and humans. A study was conducted to gain new insight into the possible sites and modes of action of flurbiprofen enantiomers. In a modified Randall Selitto assay, both enantiomers were antinociceptive in a dose-dependent manner after systemic administration. After local administration into the inflamed paw, only S-flurbiprofen produced significant dose-related antinociception. In a physiologic study, we recorded extracellularly from nociceptive spinal cord neurons that were rendered hyperexcitable. Intravenous administration of R- and S-flurbiprofen reduced responses of neurons to pressure applied to the inflamed knee and the noninflamed ankle and paw in a dose-dependent manner. When injected directly into the knee joint, only S-flurbiprofen but not R-flurbiprofen reduced responses to pressure. These results suggest a central site of antinociceptive action for R- and S-flurbiprofen and an additional peripheral site for S-flurbiprofen. The findings may be of clinical relevance, as it was demonstrated that both enantiomers also were antinociceptive in humans. Because R-flurbiprofen caused less toxicity in rats than the S-enantiomer or the racemic compound, a reduction in the quantitatively most important side effects in the gastrointestinal tract might be achieved with the use of R-flurbiprofen for pain therapy.

Analgesic effects of propyphenazone in comparison to its combination with caffeine

OBJECTIVE

The aim of the study was to investigate whether the analgesic effect of propyphenazone (PROP) was increased when it was administered in combination with caffeine (CAFF).

METHODS

For assessment of analgesia a model was chosen based on chemo-somatosensory event-related potentials (CSSERP) elicited by stimulation of the nasal mucosa. Twenty healthy volunteers participated in the experiments. The study followed a placebo-controlled, randomised, double-blind, 5-fold cross-over design. Each of the 5 medications (400 mg PROP, 600 mg PROP, 400 mg PROP + 100 mg CAFF, 600 mg PROP + 150 mg CAFF, placebo) was orally administered. Experiments were separated by at least 5 days. In addition to assessment of CSSERP, subjects estimated the intensity of the stimulus. Drug effects unrelated to nociception were monitored, and in addition, the plasma levels of PROP were also analysed.

RESULTS

While 400 mg PROP did not significantly reduce the amplitude of CSSERP in comparison to placebo, all other medications produced a significant decrease in amplitudes. For both dosages of PROP, there was a significant amplification of the antinociceptive effect of PROP by CAFF, as indicated by the decrease in CSSERP amplitude. A significant effect of the factor "drug" was also found in the spontaneous EEG, indicating an arousal reaction after CAFF. No significant differences between plasma levels of PROP were found when applied either alone or in combination with CAFF.

CONCLUSION

The significant increase in the antinociceptive effect of PROP when administered together with caffeine appears to be related either to amplification of PROP's antinociceptive actions by CAFF or an atinociceptive effect of CAFF itself.

Preclinical and clinical development of dexketoprofen

Dexketoprofen trometamol is a water-soluble salt of the dextrorotatory enantiomer of the nonsteroidal anti-inflammatory drug (NSAID) ketoprofen. Racemic ketoprofen is used as an analgesic and an anti-inflammatory agent, and is one of the most potent in vitro inhibitors of prostaglandin synthesis. This effect is due to the S(+)-enantiomer (dexketoprofen), while the R(-)-enantiomer is devoid of such activity. The pharmacokinetic profile of ketoprofen and its enantiomers was assessed in several animals species and in human volunteers. In humans, the relative bioavailability of oral dexketoprofen trometamol (12.5 and 25 mg, respectively) is similar to that of oral racemic ketoprofen (25 and 50 mg, respectively), as measured in all cases by the area under the concentration-time curve values for S(+)-ketoprofen. Dexketoprofen trometamol, given as a tablet, is rapidly absorbed, with a time to maximum plasma concentration (tmax) of between 0.25 and 0.75 hours, whereas the tmax for the S-enantiomer after the racemic drug, administered as tablets or capsules prepared with the free acid, is between 0.5 and 3 hours. Peak plasma concentrations of 1.4 and 3.1 mg/L are reached after administration of dexketoprofen trometamol 12.5 and 25 mg, respectively. From 70 to 80% of the administered dose is recovered in the urine during the first 12 hours, mainly as the acyl-glucuronoconjugated parent drug. No R(-)-ketoprofen is found in the urine after administration of dexketoprofen [S(+)-ketoprofen], confirming the absence of bioinversion of the S(+)-enantiomer in humans. in animal studies, the anti-inflammatory potency of dexketoprofen was always equivalent to that demonstrated by twice the dose of ketoprofen. Similarly, animal studies showed a high analgesic potency for dexketoprofen trometamol. The R(-)-enantiomer demonstrated a much lower potency, its analgesic action being apparent only in conditions where the metabolic bioinversion to the S(+)-enantiomer was significant. The gastric ulcerogenic effect of dexketoprofen at various oral doses (1.5 to 6 mg/kg) in the rat do not differ from those of the corresponding double doses (3 to 12 mg/kg) of racemic ketoprofen. Repeated (5-day) oral administration of dexketoprofen as the trometamol salt causes less gastric ulceration than was observed after the acid form of both dexketoprofen and the racemate. In addition, single dose dexketoprofen as the free acid at 10 to 20 mg/kg does not show a significant intestinal ulcerogenic effect in rats, while racemic ketoprofen 20 or 40 mg/kg is clearly ulcerogenic to the small intestine. The analgesic efficacy of oral dexketoprofen trometamol 10 to 20 mg is superior to that of placebo and similar to that of ibuprofen 400 mg in patients with moderate to serve pain after third molar extraction. The time to onset of pain relief appeared to be shorter in patients treated with dexketoprofen trometamol than in those treated with ibuprofen 400 mg. Dexketoprofen trometamol was well tolerated, with a reported incidence of adverse events similar to that of placebo.

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

1. The dose-related effects of azapropazone on (i) event-related and spontaneous EEG-activity and (ii) the subjects' pain ratings were investigated using an experimental human pain model based on both chemo-somatosensory event-related potentials (CSSERP) and subjects' pain ratings. 2. Healthy subjects (n = 20) participated in a placebo-controlled, randomized, double-blind, four-way cross-over study. Single doses of azapropazone (300 mg, 600 mg and 1200 mg) and placebo were administered intravenously. Each experiment consisted of five sessions (before and 1, 2, 4 and 8 h after administration of the medication). Each session lasted for approximately 40 min. In the first 20 min, pain was induced by short CO2-stimuli presented to the right nostril (phasic pain; interstimulus interval 30 s) and EEG was recorded from five positions. CSSERPs were obtained in response to painful CO2-stimuli. In the following 20 min period, tonic pain was induced by a constant stream of dry air introduced in the left nostril. Subjects rated the intensity of both phasic and tonic pain by means of a visual analogue scale. Additionally, a frequency analysis of the spontaneous EEG was performed. 3. Azapropazone reduced the pain-related CSSERP-amplitudes at frontal and parietal recording positions. This topographical pattern was observed in previous studies with opioids, while NSAIDs such as flurbiprofen and ketoprofen exerted effects at frontal and central positions. In contrast to other NSAIDs, administration of azapropazone resulted in a reduction of the frequency bands alpha 1, delta and theta of the spontaneous EEG. At the subjective level, analgesic effects of azapropazone were observed in the ratings of tonic pain. 4. Analgesic properties of azapropazone were demonstrated in man. The topographical pattern of the changes in the CSSERPs and the effects on EEG background activity suggest a central component of the analgesic action of azapropazone.