A review of the pharmacokinetic and pharmacodynamic factors in the potentiation of the antinociceptive effect of nonsteroidal anti-inflammatory drugs by caffeine

Pharmacokinetic and pharmacodynamic herb-drug interactions-part I. Herbal medicines of the central nervous system

Unlike conventional drug substances, herbal medicines are composed of a complex of biologically active compounds. Therefore, the potential occurrence of herb-drug interactions is even more probable than for drug-drug interactions. Interactions can occur on both the pharmacokinetic and pharmacodynamic level. Herbal medicines may affect the resulting efficacy of the concomitantly used (synthetic) drugs, mainly on the pharmacokinetic level, by changing their absorption, distribution, metabolism, and excretion. Studies on the pharmacodynamic interactions of herbal medicines and conventional drugs are still very limited. This interaction level is related to the mechanism of action of different plant constituents. Herb-drug interactions can cause changes in drug levels and activities and lead to therapeutic failure and/or side effects (sometimes toxicities, even fatal). This review aims to provide a summary of recent information on the potential drug interactions involving commonly used herbal medicines that affect the central nervous system (Camellia, Valeriana, Ginkgo, Hypericum, Humulus, Cannabis) and conventional drugs. The survey databases were used to identify primary scientific publications, case reports, and secondary databases on interactions were used later on as well. Search keywords were based on plant names (botanical genera), officinal herbal drugs, herbal drug preparations, herbal drug extracts.

Synergistic Effects of Caffeine in Combination with Conventional Drugs: Perspectives of a Drug That Never Ages

Plants have been known since ancient times for their healing properties, being used as preparations against human diseases of different etiologies. More recently, natural products have been studied and characterized, isolating the phytochemicals responsible for their bioactivity. Most certainly, there are currently numerous active compounds extracted from plants and used as drugs, dietary supplements, or sources of bioactive molecules that are useful in modern drug discovery. Furthermore, phytotherapeutics can modulate the clinical effects of co-administered conventional drugs. In the last few decades, the interest has increased even more in studying the positive synergistic effects between plant-derived bioactives and conventional drugs. Indeed, synergism is a process where multiple compounds act together to exert a merged effect that is greater than that of each of them summed together. The synergistic effects between phytotherapeutics and conventional drugs have been described in different therapeutic areas, and many drugs are based on synergistic interactions with plant derivatives. Among them, caffeine has shown positive synergistic effects with different conventional drugs. Indeed, in addition to their multiple pharmacological activities, a growing body of evidence highlights the synergistic effects of caffeine with different conventional drugs in various therapeutic fields. This review aims to provide an overview of the synergistic therapeutic effects of caffeine and conventional drugs, summarizing the progress reported to date.

Effect of Coffee on Lipopolysaccharide-Induced Immortalized Human Oral Keratinocytes

Periodontitis is a common inflammatory disease that is strongly influenced by dietary habits. Coffee is one of the most common dietary components; however, current research on the relationship between coffee consumption and periodontitis, as well as its underlying mechanisms, is limited. Based on a previous report, caffeine (CA) and chlorogenic acid (CGA) were formulated into artificial coffee (AC) for this experiment. Cell viability, prostaglandin E2 release, Western blotting, cellular reactive oxygen species (ROS) production, and NF-E2-related factor 2 (Nrf2) translocation analyses were performed to explore the effects of AC on lipopolysaccharide (LPS)-induced immortalized human oral keratinocytes (IHOKs) and elucidate their underlying mechanisms. AC pretreatment attenuated LPS-induced inflammatory mediator release, ROS production, and nuclear factor kappa B translocation in IHOKs. CA and CGA promoted AMP-activated protein kinase phosphorylation and down-regulated the nuclear factor-κB pathways to exert anti-inflammatory effects. Additionally, CGA promoted Nrf2 translocation and heme oxygenase-1 expression and showed anti-oxidative effects. Furthermore, AC, CA, and CGA components showed synergistic effects. Thus, we predict that coffee consumption may be beneficial for alleviating periodontitis. Moreover, the main coffee components CA and CGA seem to play a synergistic role in periodontitis.

Caffeine and rheumatoid arthritis: A complicated relationship

The current ideal goal of rheumatoid arthritis (RA) management is to resolve joint and systemic inflammation by using pharmacological interventions, assuming this will correspondingly lead to overall well-being. Nonetheless, it has emerged that a substantial number of RA patients do not reach optimal disease control. Thus suggesting the holistic management of subjective symptoms might be overlooked. This poses significant medical challenges; hence the proposal of incorporating lifestyle interventions as part of a multidimensional approach. Among these aspects, both patients and physicians perceive the important role of nutrition. This review shall examine how caffeine, one of the most studied bioactive components of the most widely consumed beverages, may potentially interfere with RA management. In particular, the mechanism by which caffeine affects RA pathogenesis, as a trigger for RA onset or flare, including its influence on rheumatic drug metabolism and the most common RA comorbidities and constitutional symptoms are outlined, highlighting important knowledge gaps and unmet research needs.

The Impact of Baseline Pain Intensity on the Analgesic Efficacy of Ibuprofen/Caffeine in Patients with Acute Postoperative Dental Pain: Post Hoc Subgroup Analysis of a Randomised Controlled Trial

Introduction

A fixed dose combination (FDC) of ibuprofen 400 mg and caffeine 100 mg has been shown to be more effective than ibuprofen 400 mg alone for the treatment of acute postoperative dental pain in a phase III randomised controlled trial. A post hoc subgroup analysis of the primary data from an active-/placebo-controlled, double-blind, single-centre, parallel-group study was conducted in patients with moderate or severe baseline pain.

Methods

After dental surgery, patients with moderate or severe pain, which was determined on a 4-point verbal rating scale (‘no pain’ to ‘severe pain’), received a single dose of ibuprofen 400 mg/caffeine 100 mg FDC, ibuprofen 400 mg, caffeine 100 mg or placebo. Pain relief (PAR) and pain intensity were assessed 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7 and 8 h after administration of study medication. The primary study endpoint was the time-weighted sum of PAR and pain intensity difference (PID) from pre-dose baseline, summed for all post-dose assessment times from 0 to 8 h (SPRID_0–8h).

Results

There were 237 patients with moderate pain and 325 with severe pain at baseline. SPRID_0–8h was significantly improved with the FDC versus ibuprofen, caffeine and placebo in the moderate and severe pain subgroups. Adjusted mean SPRID_0–8h difference for the FDC versus ibuprofen was 18.19 (p < 0.0001) for patients with moderate pain and 7.70 (p = 0.0409) for patients with severe pain. With the exception of the 7-h measurement in patients with moderate pain, PID was significantly improved with the FDC versus ibuprofen at all measured time points from 0.5 to 8 h. In the severe pain subgroup, PID was significantly improved for the FDC versus ibuprofen from 0.5 to 3 h post-dose, but was not significantly different thereafter.

Conclusion

The enhanced analgesic efficacy of ibuprofen/caffeine FDC versus ibuprofen is most pronounced in patients with moderate intensity pain at baseline, and also evident in patients with severe baseline pain.

Trial Registration

ClinicalTrials.gov identifier, NCT01929031.

The non-steroidal anti-inflammatory drug (NSAID) ibuprofen is commonly used to relieve mild to moderate pain. Research suggests that combining ibuprofen with caffeine can increase the analgesic efficacy. Previously, a randomised, double-blind, placebo-controlled study showed that this ibuprofen/caffeine combination was significantly more effective than ibuprofen alone for relieving pain after dental surgery (wisdom tooth removal). Patients in that study had moderate or severe pain, so the researchers conducted another analysis of the study data to investigate how well the ibuprofen/caffeine combination worked in patients with moderate pain and in patients with severe pain. The study found that a single dose of ibuprofen/caffeine was significantly more effective than ibuprofen alone in patients with moderate pain and in those with severe pain. The analgesic effects of ibuprofen/caffeine were more marked in patients with moderate pain than in those with severe pain. This indicates that ibuprofen/caffeine is an effective pain reliever for patients with moderate pain, and to a lesser extent in patients with severe pain.

Effect of Caffeine on the Bioavailability and Pharmacokinetics of an Acetylsalicylic Acid-Paracetamol Combination: Results of a Phase I Study

INTRODUCTION

Caffeine is used as an adjuvant in analgesic combinations to enhance their efficacy. The present study aimed to determine the effect of caffeine on the pharmacokinetics of acetylsalicylic acid (ASA) and paracetamol when used as a fixed-dose ASA/paracetamol/caffeine combination.

METHODS

In this single-centre, two-way, cross-over phase I study, volunteers fasted overnight (≥ 12 h) and randomly received single oral doses of 250 mg ASA/200 mg paracetamol (reference) or 250 mg ASA/200 mg paracetamol/50 mg caffeine (test). Blood samples were collected before and up to 24 h after dosing. The primary end points were the area under the concentration-time curve from zero to infinity (AUC0-∞) and maximum plasma concentration (Cmax) for ASA, salicylic acid (SA) and paracetamol from the two combinations. The main secondary end points were AUC0-∞ and Cmax of caffeine and time to reach Cmax (tmax) of all drugs.

RESULTS

Eighteen healthy male volunteers (32.5 ± 10.5 years) participated in the study. The geometric means of Cmax for ASA, SA and paracetamol were similar in the test (3.71, 15.8 and 2.42 µg/ml, respectively) and reference groups (3.89, 15.8, 2.42 µg/ml, respectively). The geometric mean of AUC0-∞ for ASA, SA and paracetamol from the test combination was 2.86, 60.5 and 7.68 µg h/ml, respectively, and that for the reference was 2.96, 59.1 and 7.77 µg h/ml, respectively. The medians of tmax for ASA, SA and paracetamol were similar between the two groups. The point estimates for the ratios of AUC0-∞ and Cmax for test versus reference regarding ASA, SA and paracetamol were within the predefined equivalence limits. The two treatments were well tolerated.

CONCLUSION

Caffeine did not affect the pharmacokinetics of ASA and paracetamol when used as an adjuvant in ASA/paracetamol fixed-dose combination under fasting conditions, suggesting that caffeine enhances the analgesic efficacy of these drugs by pharmacodynamic rather than pharmacokinetic interactions.

FUNDING

Sanofi-Aventis Deutschland GmbH.

Influences of smoking and caffeine consumption on trigeminal pain processing

Background

Many human and animal studies have shown the influence of nicotine and caffeine on pain perception and processing. This study aims to investigate whether smoking or caffeine consumption influences trigeminal pain processing.

Methods

Sixty healthy subjects were investigated using simultaneous recordings of the nociceptive blink reflex (nBR) and pain related evoked potentials (PREP) following nociceptive electrical stimulation on both sides of the forehead (V1). Thirty subjects were investigated before and after smoking a cigarette, as well as before and after taking a tablet of 400 mg caffeine.

Results

After smoking PREP showed decreased N2 and P2 latencies indicating central facilitation at supraspinal (thalamic or cortical) level. PREP amplitudes were not changed. NBR showed a decreased area under the curve (AUC) indicating central inhibition at brainstem level. After caffeine intake no significant changes were observed comparing nBR and PREP results before consumption.

Conclusions

Smoking influences trigeminal pain processing on supraspinal and brainstem level. In the investigated setting, caffeine consumption does not significantly alter trigeminal pain processing. This observation might help in the further understanding of the pathophysiology of pain disorders that are associated with excessive smoking habits such as cluster headache. Previous smoking has to be taken into account when performing electrophysiological studies to avoid bias of study results.

Opioid Mechanism Involvement in the Synergism Produced by the Combination of Diclofenac and Caffeine in the Formalin Model

Analgesics can be administered in combination with caffeine for improved analgesic effectiveness in a process known as synergism. The mechanisms by which these combinations produce synergism are not yet fully understood. The aim of this study was to analyze whether the administration of diclofenac combined with caffeine produced antinociceptive synergism and whether opioid mechanisms played a role in this event. The formalin model was used to evaluate the antinociception produced by the oral administration of diclofenac, caffeine, or their combination. Opioid involvement was analyzed through intracerebroventricular (i.c.v.) administration of naloxone followed by the oral administration of the study drugs. Diclofenac presented a dose-dependent effect, with a mean effective dose (ED₅₀) of 6.7 mg/kg. Caffeine presented an analgesic effect with a 17–36% range. The combination of subeffective doses of each of the two drugs presented the greatest synergism with an effect of 57.7 ± 5.6%. The maximal antinociceptive effect was obtained with the combination of 10.0 mg/kg diclofenac and 1.0 mg/kg of caffeine, with an effect of 76.7 ± 5.6%. The i.c.v. administration of naloxone inhibited the effect of diclofenac, both separately and combined. In conclusion, caffeine produces antinociceptive synergism when administered in combination with diclofenac, and this synergism is partially mediated by opioid mechanisms at the central level.

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.

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.

Caffeine does not attenuate experimentally induced ischemic pain in healthy subjects

BACKGROUND AND AIMS

Caffeine is likely the most widely used psychoactive substance in the world. It is also an analgesic adjuvant and has individual analgesic properties. The latter effect has been attributed to adenosine receptor antagonism, but the site of action is unknown. The aim of this study was to investigate the analgesic properties of caffeine on experimentally induced ischemic pain and to attempt to elucidate whether the site of action is central or peripheral.

MATERIALS AND METHODS

Seventeen healthy subjects received intravenous (i.v.) regional and systemic infusions of caffeine at 10 mg/kg or placebo in a double-blind, crossover fashion to investigate the site of action for caffeine-induced analgesia. Subjects underwent a sub-maximum effort tourniquet test. Pain scores [visual analogue scale (VAS), 0-100] were assessed every minute up to a maximum of 45 min.

RESULTS

The sum of pain scores (SPS, accumulation of VAS scores) was attenuated neither by systemic 2405 (+/-234) nor by i.v. regional caffeine 2427 (+/-190) as compared with placebo 2442 (+/-205), P=0.99 (mean+/-SEM). Time to maximal VAS score did not differ significantly between treatments, P=0.94. There was no correlation between caffeine concentration in plasma and time to maximal pain score, or between SPS and plasma concentration.

CONCLUSION

Caffeine does not have an analgesic effect on ischemic pain, either by a peripheral or by a central site of action.

Caffeine Use in Sports, Pharmacokinetics in Man, and Cellular Mechanisms of Action

Caffeine is the most widely consumed psychoactive 'drug' in the world and probably one of the most commonly used stimulants in sports. This is not surprising, since it is one of the few ergogenic aids with documented efficiency and minimal side effects. Caffeine is rapidly and completely absorbed by the gastrointestinal tract and is readily distributed throughout all tissues of the body. Peak plasma concentrations after normal consumption are usually around 50 microM, and half-lives for elimination range between 2.5-10 h. The parent compound is extensively metabolized in the liver microsomes to more than 25 derivatives, while considerably less than 5% of the ingested dose is excreted unchanged in the urine. There is, however, considerable inter-individual variability in the handling of caffeine by the body, due to both environmental and genetic factors. Evidence from in vitro studies provides a wealth of different cellular actions that could potentially contribute to the observed effects of caffeine in humans in vivo. These include potentiation of muscle contractility via induction of sarcoplasmic reticulum calcium release, inhibition of phosphodiesterase isoenzymes and concomitant cyclic monophosphate accumulation, inhibition of glycogen phosphorylase enzymes in liver and muscle, non-selective adenosine receptor antagonism, stimulation of the cellular membrane sodium/potassium pump, impairment of phosphoinositide metabolism, as well as other, less thoroughly characterized actions. Not all, however, seem to account for the observed effects in vivo, although a variable degree of contribution cannot be readily discounted on the basis of experimental data. The most physiologically relevant mechanism of action is probably the blockade of adenosine receptors, but evidence suggests that, at least under certain conditions, other biochemical mechanisms may also be operational.

Comparative study between capillary electrophoresis and high performance liquid chromatography in ‘guarana’ based phytopharmaceuticals

The last years have seen a significant increase in the use of herbal medicines and their preparations all over the world. Adulterations with synthetic drugs are common problems with phytopharmaceutical products and this can potentially cause adverse effects. In consequence, it is important to determine the presence of synthetic drugs in herbal medicines to ensure their efficacy and safety. In this study, guarana derivatives were analyzed by capillary electrophoresis (CE), and the results were compared with those obtained by the HPLC technique. In order to obtain adequate fingerprints, and search for adulterants, caffeine was used as the marker compound. This separation method was applied to analyze the seed powder and commercial tablets of Paulinia cupana Mart. The methodology performance was evaluated in terms of specificity, sensitivity and precision. The results are in agreement with those obtained by the HPLC method. Furthermore, the analysis time of the CE method is up to two times shorter than the respective parameter in HPLC and solvent consumption is more than 100-fold less.

4-Caffeoyl-1,5-quinide in roasted coffee inhibits [3H]naloxone binding and reverses anti-nociceptive effects of morphine in mice

RATIONALE

Cinnamoylquinides are formed from the corresponding chlorogenic acids during coffee roasting. Instant coffee has been shown to displace binding of the mu opioid receptor antagonist, [3H]naloxone, but the putative active agent, feruloylquinide, has not been characterized.

OBJECTIVES

The goal was to identify the active agent(s) in coffee by measuring the binding affinity of individual cinnamoyl-1,5-quinides to the human mu opioid receptor, and determine the effects of these compounds on morphine-induced anti-nociceptive behavior in mice.

METHODS

Cinnamoyl-1,5-quinides in extracts of decaffeinated instant coffee were quantified by reverse-phase HPLC comparisons with synthetic samples of 3-coumaroyl-1,5-quinide and 4-coumaroyl-1,5-quinide, 3-caffeoyl-1,5-quinide and 4-caffeoyl-1,5-quinide (4-CQL) 3-feruloyl-1,5-quinide and 4-feruloyl-1,5-quinides and 3,4-dicaffeoyl-1,5-quinide (DICAQ). Affinities of the cinnamoyl-1,5-quinides and decaffeinated instant coffee extract were determined by displacement of [3H]naloxone binding in cultured HEK-MOR cells. Inhibition of the anti-nociceptive activity of morphine (1 mg/kg IP) was determined in C57BL/6J mice using the hot plate test at 52 degrees C.

RESULTS

Extract of decaffeinated instant coffee produced a displacement K(i) of 42+/-16 mg/l, while the K(i) of a synthetic sample of 4-CQL was 4.4+/-0.4 microM. Compounds with a cinnamoyl substituent in the 4-position of the quinide, i.e. 4-CQL, DICAQ, 3,4-diferuloyl-1,5-quinide, and 3,4-dicoumaroyl-1,5-quinide, had affinities for the mu opioid receptor in the low micromolar range. In the hot plate test, coffee extract, containing 0.78% of 4-CQL, reversed the anti-nociceptive effect of morphine at 10 mg/kg IP. Two cinnamoyl-1,5-quinides found in roasted coffee, DICAQ, and 4-CQL, were active at 1 and 0.1 mg/kg IP, respectively.

CONCLUSIONS

These results suggest that the previously reported anti-opioid activity of instant coffee is caused primarily by the presence of 4-CQL, and to lesser extent by other cinnamoyl-1,5-quinides.

Antinociception and the new COX inhibitors: research approaches and clinical perspectives

New generations of cyclooxygenase (COX) inhibitors are more potent and efficacious than their traditional parent compounds. They are also safer than the classic non-steroidal anti-inflammatory drugs (NSAIDs) and are starting to be used not only for low to moderate intensity pain, but also for high intensity pain. Three different strategies have been followed to improve the pharmacological profile of COX inhibitors: 1. Development of COX-2 selective inhibitors. This is based on the initial hypothesis that considered COX-2 as the enzyme responsible for the generation of prostaglandins only in inflammation, and, therefore, uniquely responsible for inflammation, pain and fever. Initial expectations gave rise to controversial results, still under discussion. The second generation of these compounds is being developed and should contribute to clarifying both their efficacy and the specific functions of the COX enzymes. 2. Modified non-selective COX inhibitors. Molecules like nitro-NSAIDs or tromethamine salt derivatives have been synthesized considering that both COX-1 and COX-2 are responsible for the synthesis of prostaglandins involved either in homeostatic functions or inflammation. Nitroaspirin, nitroparacetamol or dexketoprofen trometamol are some examples of molecules that are already showing an important clinical efficacy. The modifications performed in their structures seem to lower the unwanted side effects as well as to enhance their analgesic efficacy. 3. Combined therapy of classic NSAIDs with other drugs. This strategy looks for improvements in the incidence of adverse effects or to take advantage of the synergistic enhancement of their therapeutic effects. Some of the molecules resulting from these strategies are very valuable as therapeutic agents and open a wide range of possibilities in the treatment of high intensity pain, including neuropathic pain, and opiate sparing therapy.

Inhibition of prostaglandin biosynthesis in human endotoxin-stimulated peripheral blood monocytes: effects of caffeine

There is an ongoing debate about possible advantages of the coadministration of caffeine with cyclooxygenase (COX) inhibitors in the treatment of pain. There are results suggesting interference by caffeine with COX expression and activity in rat immune cells. In the present study, we have used, therefore, human endotoxin-stimulated monocytes to investigate a possible influence of caffeine on indometacin-induced inhibition of prostaglandin E(2) (PGE(2)) formation. Endotoxin caused a concentration- and time-dependent increase in immunoreactive PGE(2) that was dependent on CD14-mediated mechanisms. In order to investigate pharmacological inhibition of the COX activity, a submaximal concentration of 1 ng/ml endotoxin (4 h exposure time) was used. Indometacin caused a concentration-dependent inhibition of PGE(2) with an apparent IC(50) of 8.9 +/- 1.4 x 10(-9) mol/l and an I(max) of 1 x 10(-7) mol/l. Caffeine (5 x 10(-6) to 1.5 x 10(-4) mol/l) on its own produced no statistically significant effect on endotoxin-induced PGE(2) formation. In the presence of caffeine (5 x 10(-6) to 1.5 x 10(-4) mol/l), inhibition of PGE(2) biosynthesis by indometacin (1 x 10(-8) mol/l) was not significantly altered. These results show that, in human monocytes, caffeine, up to concentrations severalfold higher than those reached in patients, has no significant effect on endotoxin-induced PGE(2) formation nor on its inhibition by indometacin.

Indomethacin, caffeine and prochlorperazine alone and combined revert hyperalgesia in in vivo models of migraine

The combination of indomethacin, caffeine, and prochlorperazine (hereinafter IndoProCaf) represents an effective antimigraine drug available on the Italian market. The aim of this study was to test the efficacy of the three active principles alone and in combination in reverting hyperalgesia. Hyperalgesia was induced by morphine withdrawal in mice treated with morphine for 15 days and then made hyperalgic by morphine substitution with water. This study showed that indomethacin 0.3 mg kg(-1), i.p.; caffeine 0.1 and 0.3 mg kg(-1), i.p.; and prochlorperazine 0.1 mg kg(-1), i.p.; as well as the combination of the three active principles, were able to revert morphine withdrawal induced hyperalgesia, causing a statistically significant increase of pain threshold in hyperalgic mice. In a second model, hyperalgesia was induced by the i.p. injection of a 0.3% solution of acetic acid in mice and was evaluated counting the number of abdominal constrictions. Indomethacin (0.1 mg kg(-1), i.p.), caffeine (0.3 mg kg(-1), i.p.), and prochlorperazine (0.1 mg kg(-1), i.p.) reduced the number of abdominal constrictions, while the combination of the three active principles was able to abolish almost completely the abdominal constrictions, with a significantly higher efficacy compared to the single active principles. In both models, indomethacin, caffeine, and prochlorperazine reverted hyperalgesia at dosages 10 times lower than the corresponding analgesic ones. These data provide the pharmacologic evidence of the efficacy of IndoProCaf in reverting hyperalgesia, a condition of reduction of pain threshold similar to that occurring in migraine.

A benefit-risk assessment of caffeine as an analgesic adjuvant

Caffeine has been an additive in analgesics for many years. However, the analgesic adjuvant effects of caffeine have not been seriously investigated since a pooled analysis conducted in 1984 showed that caffeine reduces the amount of paracetamol (acetaminophen) necessary for the same effect by approximately 40%. In vitro and in vivo pharmacological research has provided some evidence that caffeine can have anti-nociceptive actions through blockade of adenosine receptors, inhibition of cyclo-oxygenase-2 enzyme synthesis, or by changes in emotion state. Nevertheless, these actions are only considered in some cases. It is suggested that the actual doses of analgesics and caffeine used can influence the analgesic adjuvant effects of caffeine, and doses that are either too low or too high lead to no analgesic enhancement. Clinical trials suggest that caffeine in doses of more than 65 mg may be useful for enhancement of analgesia. However, except for in headache pain, the benefits are equivocal. While adding caffeine to analgesics increases the number of patients who become free from headache [rate ratio = 1.36, 95% confidence interval (CI) 1.17 to 1.58], it also leads to more patients with nervousness and dizziness (relative risk = 1.60, 95% CI 1.26 to 2.03). It is suggested that long-term use or overuse of analgesic medications is associated with rebound headache. However, there is no robust evidence that headache after use or withdrawal of caffeine-containing analgesics is more frequent than after other analgesics. Case-control studies have shown that caffeine-containing analgesics are associated with analgesic nephropathy (odds ratio = 4.9, 95% CI 2.3 to 10.3). However, no specific contribution of caffeine to analgesic nephropathy can be identified from these studies. Whether caffeine produces nephrotoxicity on its own, or increases nephrotoxicity due to analgesics, is yet to be established.