Enhancement of antinociception by co-administration of ibuprofen and caffeine in arthritic rats

Design, synthesis, analgesic, antibacterial and docking studies of novel 8-piperazinylcaffeine carboxylate ionic liquids

This paper presents a comprehensive evaluation of novel 8-piperazinylcaffeine carboxylate ionic liquids, including their design, synthesis, characterization, analgesic and antibacterial properties, as well as docking studies. These unique salts were produced by combining 8-piperazinyl caffeine (8-PC) with various carboxylic acids, some of which are commonly used nonsteroidal anti-inflammatory drugs (NSAIDs). Through in vivo experiments on female mice using the formalin test, the analgesic efficacy of different 8-PC salts with various NSAIDs was assessed. Results demonstrated that a majority of these salts exhibited significant analgesic activity when compared to NaIBP, a standard reference drug. Particularly noteworthy was the enhanced analgesic effect of the 8-PC's NSAIDs salts (11a, 11c-e, and 11k) compared to their corresponding sodium salts, which was attributed to the presence of the 8-PC cation (synergistic effect). Furthermore, all synthesized salts were subjected to in vitro testing against Gram-positive Staphylococcus aureus (PTCC 1133), Gram-negative Pseudomonas aeruginosa (ATCC 27853), and Escherichia coli (PTCC 1330) bacteria. Among them, salt 11k displayed notable antibacterial activity, especially against P. aeruginosa, a dangerous opportunistic pathogen. Additionally, docking analysis revealed strong binding of the synthesized 8-PC and NSAID salts to the active site of the COX-2 enzyme.

Caffeine Attenuates Electroacupuncture Effect on Pressure Pain Threshold and Tolerance in Healthy Individuals: A Randomized Controlled Trial

Introduction

The effect of caffeine on acupuncture analgesia in humans is unclear. This study aimed to investigate whether caffeine-containing beverage intake influences the effect of electroacupuncture (EA) on static quantitative sensory testing (QST) and dynamic QST in healthy subjects.

Methods

A total of 40 healthy subjects were enrolled and randomly assigned to receive coffee containing moderate doses of caffeine (coffee group) or non-caffeinated juice (juice group) for 4 weeks. The primary outcome measures were the pressure pain threshold (PPT), pressure pain tolerance (PPTo), and heat pain threshold (HPT) as static QST parameters. Numerical rating scales (NRS) of heat stimulus and nociceptive flexor reflex (RIII reflex), as parameters of dynamic QST, were also examined. EA stimulation with tolerance intensity was performed at ST36 (Zusanli)-GB34 (Yanglingquan) points at weeks 0, 2, and 4. PPT, PPTo, and HPT were detected pre- and post- EA. The NRS scores were examined pre-, during, and post-EA, and 1 min after EA was completed. The RIII reflex was examined pre- and 1–5 min post-EA.

Results

At week 0, both groups showed increased PPT and PPTo and decreased NRS scores of heat stimuli and RIII reflex after EA, but HPT was not affected. After 4 weeks, the effects of EA on PPT and PPTo were attenuated in the coffee group compared to the juice group, whereas the effect of EA on the NRS scores and RIII reflex were not influenced. There was no significant difference found at week 2 for these indications. EA also did not affect the HPT in both groups at week 4.

Conclusion

Moderate caffeine intake reduced the effects of EA on PPT and PPTo in healthy subjects.

Pharmacokinetics and Pharmacodynamics of (S)-Ketoprofen Co-Administered with Caffeine: A Preclinical Study in Arthritic Rats

The purpose of the present study was to determine whether caffeine modifies the pharmacokinetics and pharmacodynamics of (S)-ketoprofen following oral administration in a gout-type pain model. 3.2 mg/kg of (S)-ketoprofen alone and combined with 17.8 mg/kg of caffeine were administered to Wistar rats and plasma levels were determined between 0.5 and 24.0 h. Additionally, antinociception was evaluated based on the protocol of the PIFIR (pain-induced functional impairment in the rat) model before blood sampling between 0.5 and 4.0 h. Significant differences in C_max, AUC_0-24, and AUC_0-∞ values were observed with caffeine administration (p < 0.05). Also, significant differences in E_max, T_max, and AUC_0-4 values were determined when comparing the treatments with and without caffeine (p < 0.05). By relating the pharmacokinetic and pharmacodynamic data, a counter-clockwise hysteresis loop was observed regardless of the administration of caffeine. When the relationship between AUCe and AUCp was fitted to the sigmoidal E_max model, a satisfactory correlation was found (R² > 0.99) as well as significant differences in E_max and EC₅₀ values (p < 0.05). With caffeine, E_max and EC₅₀ values changed by 489.5% and 695.4%, respectively. The combination studied represents a convenient alternative for the treatment of pain when considering the advantages offered by using drugs with different mechanisms of action.

Caffeine in the management of patients with headache

Caffeinated headache medications, either alone or in combination with other treatments, are widely used by patients with headache. Clinicians should be familiar with their use as well as the chemistry, pharmacology, dietary and medical sources, clinical benefits, and potential safety issues of caffeine. In this review, we consider the role of caffeine in the over-the-counter treatment of headache. The MEDLINE and Cochrane databases were searched by combining “caffeine” with the terms “headache,” “migraine,” and “tension-type.” Studies that were not placebo-controlled or that involved medications available only with a prescription, as well as those not assessing patients with migraine and/or tension-type headache (TTH), were excluded. Compared with analgesic medication alone, combinations of caffeine with analgesic medications, including acetaminophen, acetylsalicylic acid, and ibuprofen, showed significantly improved efficacy in the treatment of patients with TTH or migraine, with favorable tolerability in the vast majority of patients. The most common adverse events were nervousness (6.5%), nausea (4.3%), abdominal pain/discomfort (4.1%), and dizziness (3.2%). This review provides evidence for the role of caffeine as an analgesic adjuvant in the acute treatment of primary headache with over-the-counter drugs, caffeine doses of 130 mg enhance the efficacy of analgesics in TTH and doses of ≥100 mg enhance benefits in migraine. Additional studies are needed to assess the relationship between caffeine dosing and clinical benefits in patients with TTH and migraine.

Pharmacologic synergism of ocular ketorolac and systemic caffeine citrate in rat oxygen-induced retinopathy

BACKGROUND

Caffeine or ketorolac decrease the risk of retinopathy of prematurity and may act synergistically to improve beneficial effect. Combination of caffeine (Caff) and ketorolac (Keto) to prevent oxygen-induced retinopathy was studied.

METHODS

Newborn rats exposed to room air (RA) or intermittent hypoxia (IH) consisting of 12% O2 during hyperoxia (50% O2) from birth (P0) had single daily IP injections of Caff from P0-P13 or saline; and/or ocular Keto (Acuvail, 0.45% ophthalmic solution) administered subcutaneously over the eyes from P5-P7. Pups were studied at P14 or placed in RA for recovery from IH (IHR) until P21. Eyes were examined for neovascularization, histopathology, growth factors, and VEGF-signaling genes.

RESULTS

Severe retinal damage noted during IHR in the untreated groups evidenced by hemorrhage, neovascularization, and oxygen-induced retinopathy (OIR) pathologies were prevented with Keto/Caff treatment. Keto and/or Caff treatment in IH also promoted retinal neural development evidenced by eye opening (92%, P < 0.001 vs. 31% in the placebo-treated IH group). No corneal pathologies were noted with Keto.

CONCLUSION

Caff or Keto given individually reduced retinal neovascularization, but the two drugs given together prevented severe OIR.

Subjective evaluation of the frequency of coffee intake and relationship to osteoporosis in Chinese men

BACKGROUND

The main purpose of this study was to evaluate the associations between frequency of coffee intake and osteoporosis (OP) in a general Chinese male sample.

METHODS

We conducted a large-scale, community-based, cross-sectional study to investigate the associations by using a self-report questionnaire to estimate the frequency of coffee intake. A total of 992 men were available for data analysis in this study. Multiple regression models controlling for confounding factors to include frequency of coffee intake variable were performed to investigate the relationships for OP.

RESULTS

Positive correlations between frequency of coffee intake and T-score were reported (β = 0.211, P = 0.024). Multiple regression analysis indicated that the frequency of coffee intake was significantly associated with OP (P < 0.05 for model 1 and model 2). The men with moderate frequency of coffee intake had a lower prevalence of OP.

CONCLUSIONS

The findings indicated that consumption of coffee was independently and significantly associated with OP. The prevalence of OP was less frequent in Chinese men with moderate coffee intake.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT02451397.

Antinociceptive Effect of Racemic Flurbiprofen and Caffeine Co-Administration in an Arthritic Gout-Type Pain in Rats

Preclinical Research Drug combinations are routinely used in the treatment of pain. In drug associations, adjuvants such as caffeine, are employed with different non-steroidal anti-inflammatories drugs (NSAIDs), however, at present does not exist studies showing the effect of the combination of racemic flurbiprofen (rac-Flur) in association with caffeine. The objective of this work was to evaluate the combination of rac-Flur + caffeine oral in arthritic gout-type pain in rats. The antinociceptive effects of the rac-Flur alone and in combination with caffeine were analyzed on a pain-induced functional impairment model in rat. rac-Flur induced a dose-dependent antinociceptive effect and caffeine did not present any effect. The combination of rac-Flur and caffeine achieve a higher percentage of antinociceptive effect compared with the individual administration of rac-Flur. The dose-response curve (DRCs) shows that the combination of rac-Flur (31.6 mg/kg) + caffeine (17.8 mg/kg) exhibited the maximal antinociceptive efficacy (294.0 ± 21.2 area units), while rac-Flur alone (31.6 mg/kg) showed 207.2 ± 35.2 au, thus indicating an increase in efficacy (potentiation). Furthermore, the DRCs of the combinations presented a displacement to the left, indicating a change in the potency. Caffeine is able to increase the effect of rac-Flur in the arthritic gout-type pain in rats. Drug Dev Res 77 : 192-198, 2016.   © 2016 Wiley Periodicals, Inc.

Pharmacologic interventions for the prevention and treatment of retinopathy of prematurity

Retinopathy of prematurity (ROP), a significant morbidity in prematurely born infants, is the most common cause of visual impairment and blindness in children and persists till adulthood. Strict control of oxygen therapy and prevention of intermittent hypoxia are the keys in the prevention of ROP, but pharmacologic interventions have decreased risk of ROP. Various drug classes such as methylxanthines (caffeine), VEGF inhibitors, antioxidants, and others have decreased ROP occurrence. The timing of pharmacologic intervention remains unsettled, but early prevention rather than controlling disease progression may be preferred. These drugs act through different mechanisms, and synergistic approaches should be considered to maximize efficacy and safety.

Environmentally oriented models and methods for the evaluation of drug × drug interaction effects

This detailed review compares known and widely used methods for drug interaction estimation, some of which now have historical significance. Pharmaceutical application has been noted as far back as several thousand years ago. Relatively late in the 20th century, however, researchers became aware that their fate and metabolism, which still remain a great challenge for environmental analysts and risk assessors. For the patient's well-being, treatment based on the mixing of drugs has to be effective and should not cause any side effects (or side effects should not have a significant impact on health and mortality). Therefore, it is important to carefully examine drugs both individually and in combinations. It should be also stated that application form/way of entering the living organism is of great importance as well as the age and the place in the trophic system of the organism in order to eliminate harmful dosages in the case of infants' accidental intoxication.

Single dose oral ibuprofen plus caffeine for acute postoperative pain in adults

BACKGROUND

There is good evidence that combining two different analgesics in fixed doses in a single tablet can provide better pain relief in acute pain and headache than either drug alone, and that the drug-specific benefits are essentially additive. This appears to be broadly true in postoperative pain and migraine headache across a range of different drug combinations, and when tested in the same and different trials. Adding caffeine to analgesics also increases the number of people obtaining good pain relief. Combinations of ibuprofen and caffeine are available without prescription in some parts of the world.

OBJECTIVES

To assess the analgesic efficacy and adverse effects of a single oral dose of ibuprofen plus caffeine for moderate to severe postoperative pain, using methods that permit comparison with other analgesics evaluated in standardised trials using almost identical methods and outcomes.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, the Oxford Pain Relief Database, two clinical trial registries, and the reference lists of articles. The date of the most recent search was 1 February 2015.

SELECTION CRITERIA

Randomised, double-blind, placebo- or active-controlled clinical trials of single dose oral ibuprofen plus caffeine for acute postoperative pain in adults.

DATA COLLECTION AND ANALYSIS

Two review authors independently considered trials for inclusion in the review, assessed risk of bias, and extracted data. We used the area under the pain relief versus time curve to derive the proportion of participants with at least 50% pain relief over six hours prescribed either ibuprofen plus caffeine or placebo. We calculated the risk ratio (RR) and number needed to treat to benefit (NNT). We used information on the use of rescue medication to calculate the proportion of participants requiring rescue medication and the weighted mean of the median time to use. We also collected information on adverse effects.

MAIN RESULTS

We identified five randomised, double-blind studies with 1501 participants, but only four had been published and had relevant outcome data. These four studies were of high quality, although two of the studies were small.Both ibuprofen 200 mg + caffeine 100 mg and ibuprofen 100 mg + caffeine 100 mg produced significantly more participants than placebo who achieved at least 50% of maximum pain relief over six hours, and both doses significantly reduced remedication rates (moderate quality evidence). For at least 50% of maximum pain relief, the NNT was 2.1 (95% confidence interval 1.8 to 2.5) for ibuprofen 200 mg + caffeine 100 mg (four studies, 334 participants) and 2.4 (1.9 to 3.1) for ibuprofen 100 mg + caffeine 100 mg (two studies, 200 participants) (moderate quality evidence). These values were close to those predicted by published models for combination analgesics in acute pain, and were supported by low (good) NNT values for prevention of remedication.Adverse event rates were low, and no sensible analysis was possible.

AUTHORS' CONCLUSIONS

For ibuprofen 200 mg + caffeine 100 mg particularly, the low NNT value is among the lowest (best) values for analgesics in this pain model. The combination is not commonly available, but can be probably be achieved by taking a single 200 mg ibuprofen tablet with a cup of modestly strong coffee or caffeine tablets. In principle, this can deliver good analgesia at lower doses of ibuprofen.

Tramadol and Tramadol+Caffeine Synergism in the Rat Formalin Test Are Mediated by Central Opioid and Serotonergic Mechanisms

Different analgesic combinations with caffeine have shown this drug to be capable of increasing the analgesic effect. Many combinations with nonsteroidal anti-inflammatory drugs (NSAIDs) have been carried out, but, in regard to opioids, only combinations with morphine and tramadol have been reported. The antinociceptive synergism mechanism of these combinations is not well understood. The purpose of the present study was to determine the participation of spinal and supraspinal opioidergic and serotonergic systems in the synergic effect of the tramadol+caffeine combination in the rat formalin test. At the supraspinal level, the opioid antagonist, naloxone, completely reversed the effect of the drug combination, whereas ketanserin, a 5-HT₂ receptor antagonist, inhibited the effect by 60%; however, ondansetron, a 5-HT₃ receptor antagonist, did not alter the combination effect. When the antagonists were intrathecally administered, there was a significant reduction in all tramadol-caffeine combination effects. With respect to tramadol alone, there was significant participation of the opioid system at the supraspinal level, whereas it was the serotonergic system that participated at the spinal level by means of the two receptors studied. In conclusion, the tramadol+caffeine combination synergically activated the opioid and serotonergic systems at the supraspinal level, as well as at the spinal level, to produce the antinociception.

Adjuvant effect of caffeine on acetylsalicylic acid anti-nociception: Prostaglandin E2 synthesis determination in carrageenan-induced peripheral inflammation in rat

In the present study, we report a synergistic interaction between acetylsalicylic acid (ASA) and caffeine (CAF) on the inhibition of nociception in a model of peripheral inflammation in rat; on the contrary no interaction have been found on anti-inflammatory effects and peripheral prostaglandin E2 (PGE-2) synthesis inhibition. Acute inflammation was induced by the subplantar injection of carrageenan into the right hind paw, and the effects of the drugs were evaluated from 0 to 5h. Nociception was assessed using the Randall & Selitto test, and the inflammatory response by plethismometry. Oral administration of ASA (10-400mg/kg) induced dose-related anti-nociceptive and anti-inflammatory effects. On the other hand, oral CAF administration (5-50mg/kg) did not show a dose-related inhibitory effect, neither on the inhibition of nociception nor on the inflammatory response. To analyze a possible interaction between both drugs a dose-response curve to ASA plus a fixed dose of CAF (5mg/kg) was obtained 3h after the injection of carrageenan, when the inflammatory pain peaked. A fixed dose of CAF was able to improve the anti-nociceptive, but not the anti-inflammatory, effects of ASA. We also assessed, by enzyme immunoassay, the effects of the combination on peripheral PGE-2 levels: CAF did not alter the inhibitory effect of ASA on PGE-2 synthesis. Our results corroborate the well-known clinical effects of combining ASA and CAF; on the other hand, we rule out that prostaglandin synthesis inhibition at peripheral sites would be the mechanism responsible of the adjuvant anti-nociceptive effect of CAF.

The effects of ibuprofen and the neurokinin-1 receptor antagonist GR205171A on Fos expression in the ferret trigeminal nucleus following tooth pulp stimulation

We have developed a model to study central changes following inflammation of the tooth pulp in the ferret and have examined Fos expression in the trigeminal nucleus following stimulation of non-inflamed and inflamed tooth pulps. The aim of this study was to establish the ability of this model to predict analgesic efficacy in clinical studies of inflammatory pain. We addressed this by assessing the effects of the neurokinin-1 receptor antagonist GR205171A and ibuprofen on Fos expression following stimulation of the inflamed pulp and comparing this with known analgesic efficacy. Adult ferrets were prepared under anaesthesia to allow tooth pulp stimulation, recording from the digastric muscle and intravenous injections at a subsequent experiment. In some animals pulpal inflammation was induced, by introducing human caries into a deep buccal cavity. After 5 days, animals were reanaesthetised, treated with vehicle, GR205171A or ibuprofen and the teeth were stimulated at ten times the threshold of the jaw-opening reflex. Stimulation of all tooth pulps induced ipsilateral Fos in trigeminal subnuclei caudalis and oralis. GR205171A had no significant effect on Fos expression in the trigeminal nucleus of animals with either non-inflamed or inflamed tooth pulps. Ibuprofen reduced Fos expression in the trigeminal nucleus and this effect was most marked in animals with pulpal inflammation. These results differ from those previously described using a range of other animal models, but agree with known clinical efficacy of neurokinin-1 receptor antagonists and ibuprofen. Therefore this model is likely to be of use in accurately predicting the analgesic efficacy of novel compounds.

Methylxanthines and pain

Caffeine, an antagonist of adenosine A(1), A(2A) and A(2B) receptors, is known as an adjuvant analgesic in combination with non-steroidal anti-inflammatory drugs (NSAIDs) and acetaminophen in humans. In preclinical studies, caffeine produces intrinsic antinociceptive effects in several rodent models, and augments the actions of NSAIDs and acetaminophen. Antagonism of adenosine A(2A) and A(2B) receptors, as well as inhibition of cyclooxygenase activity at some sites, may explain intrinsic antinociceptive and adjuvant actions. When combined with morphine, caffeine can augment, inhibit or have no effect depending on the dose, route of administration, nociceptive test and species; inhibition reflects spinal inhibition of adenosine A(1) receptors, while augmentation may reflect the intrinsic effects noted above. Low doses of caffeine given systemically inhibit antinociception by several analgesics (acetaminophen, amitriptyline, oxcarbazepine, cizolirtine), probably reflecting block of a component of action involving adenosine A(1) receptors. Clinical studies have demonstrated adjuvant analgesia, as well as some intrinsic analgesia, in the treatment of headache conditions, but not in the treatment of postoperative pain. Caffeine clearly exhibits complex effects on pain transmission; knowledge of such effects is important for understanding adjuvant analgesia as well as considering situations in which dietary caffeine intake may have an impact on analgesic regimens.

An overview of clinical pharmacology of Ibuprofen

Ibuprofen was the first member of Propionic acid derivatives introduced in 1969. It is a popular domestic and over the counter analgesic and antipyretic for adults and children. Ibuprofen has been rated as the safest conventional NSAID by spontaneous adverse drug reaction reporting systems in the UK. This article summarizes the main pharmacological effects, therapeutical applications and adverse drug reactions, drug-drug interactions and food drug interactions of ibuprofen that have been reported especially during the last 10 years.

Evaluation of the efficacy and safety of a statin/caffeine combination against H5N1, H3N2 and H1N1 virus infection in BALB/c mice

The development of novel antiviral drugs is necessary for the prevention and treatment of a potential avian influenza pandemic. The aim of this study was to evaluate the efficacy and safety of a novel statin/caffeine combination against H5N1, H3N2 and H1N1 virus infection in a murine model. In H5N1-, H3N2- and H1N1-infected BALB/c mice, 50mug statin/200mug caffeine effectively ameliorated lung damage and inhibited viral replication and was at least as effective as oseltamivir and ribavirin. The statin/caffeine combination also appeared to be more effective when administered preventatively rather than as treatment. These findings provide justification for further research into this novel antiviral formulation.

Ibuprofen enhances recovery from spinal cord injury by limiting tissue loss and stimulating axonal growth

The GTP-binding protein RhoA regulates microfilament dynamics in many cell types and mediates the inhibition of axonal regeneration by myelin and chondroitin sulfate proteoglycans. Unlike most other nonsteroidal anti-inflammatory drugs, ibuprofen suppresses basal RhoA activity (Zhou et al., 2003). A recent report suggested that ibuprofen promotes corticospinal axon regeneration after spinal cord injury (Fu et al., 2007). Here, we confirm that ibuprofen reduces ligand-induced Rho signaling and myelin-induced inhibition of neurite outgrowth in vitro. Following 4 weeks of subcutaneous administration of ibuprofen, beginning 3 days after spinal cord contusion, animals recovered walking function to a greater degree, with twice as many rats achieving a hind limb weight-bearing status. We examined the relative role of tissue sparing, axonal sprouting, and axonal regeneration in the action of ibuprofen. Histologically, ibuprofen-treated animals display an increase in spared tissue without an alteration in astrocytic or microglial reaction. Ibuprofen increases axonal sprouting from serotonergic raphespinal axons, and from rostral corticospinal fibers in the injured spinal cord, but does not permit caudal corticospinal regeneration after spinal contusion. Treatment of mice with complete spinal cord transection demonstrates long-distance raphespinal axon regeneration in the presence of ibuprofen. Thus, administration of ibuprofen improves the recovery of rats from a clinically relevant spinal cord trauma by protecting tissue, stimulating axonal sprouting, and allowing a minor degree of raphespinal regeneration.

Co-administration of rofecoxib and tramadol results in additive or sub-additive interaction during arthritic nociception in rat

Over the decades, nonsteroidal anti-inflammatory drugs (NSAIDs) and opioids are the most commonly used analgesics in the management of acute and chronic pain. In order to assess a possible antinociceptive interactions, the antinociceptive effects of rofecoxib p.o., a preferential inhibitor of cyclooxygenase-2, and tramadol-hydrochloride p.o., an atypical opioid analgesic, administered either separately or in combination, were determined using a rat model of arthritic pain. The data were interpreted using the surface of synergistic interaction (SSI) analysis and an isobolographic analysis to establish the nature of the interaction. The SSI was calculated from the total antinociceptive effect produced by the combination after subtraction of the antinociceptive effect produced by each individual drug. Female rats received orally rofecoxib alone (1.0, 1.8, 3.2, 5.6, 10.0, 17.8, 31.6 and 56.2 mg/kg), tramadol alone (1.8, 3.2, 5.6, 10.0, 17.8, 31.6 and 56.2 mg/kg) or 12 different combinations of rofecoxib plus tramadol. Five combinations exhibited various degrees of sub-additive (i.e. less than the sum of the effects produced by the each drug alone) antinociceptive effects (3.2 mg/kg tramadol with 7.8 mg/kg rofecoxib; 5.6 mg/kg tramadol with either 10.0 or 17.8 mg/kg rofecoxib; 10.0 mg/kg tramadol with either 10.0 or 17.8 mg/kg rofecoxib), whereas the other 7 combinations showed additive antinociceptive effects (i.e. the sum of the effects produced by each agent alone). Three combination of rofecoxib+tramadol (10.0+5.6, 10.0+10.0, and 17.8+5.6 mg/kg respectively) presented high sub-additive interactions (P<0.002: Q=9.5). The combination rofecoxib (17.8 mg/kg)+tramadol (10.0 mg/kg) caused gastric injuries less severe than those observed with indomethacin, but more severe than those obtained with rofecoxib or tramadol in single administration. The antinociceptive interaction of rofecoxib and tramadol suggests that combinations with these drugs may have no clinical utility in pain therapy.