Caffeine and pain

Caffeine as an analgesic adjuvant for acute pain in adults

BACKGROUND

This is an updated version of the original Cochrane review published in Issue 3, 2012. Caffeine has been added to common analgesics such as paracetamol, ibuprofen, and aspirin, in the belief that it enhances analgesic efficacy. Evidence to support this belief is limited and often based on invalid comparisons.

OBJECTIVES

To assess the relative efficacy of a single dose of an analgesic plus caffeine against the same dose of the analgesic alone, without restriction on the analgesic used or the pain condition studied. We also assessed serious adverse events.

SEARCH METHODS

We searched CENTRAL, MEDLINE, and EMBASE from inception to 28 August 2014, the Oxford Pain Relief Database, and also carried out Internet searches and contacted pharmaceutical companies known to have carried out trials that have not been published.

SELECTION CRITERIA

We included randomised, double-blind studies that compared a single dose of analgesic plus caffeine with the same dose of the analgesic alone in the treatment of acute pain.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed the eligibility and quality of studies, and extracted data. Any disagreements or uncertainties were settled by discussion with a third review author. We sought any validated measure of analgesic efficacy, but particularly the number of participants experiencing at least 50% of the maximum possible pain relief over four to six hours, participants reporting a global evaluation of treatment of very good or excellent, or headache relief after two hours. We pooled comparable data to look for a statistically significant difference, and calculated numbers needed to treat to benefit (NNT) with caffeine. We also looked for any numerical superiority associated with the addition of caffeine, and information about any serious adverse events.

MAIN RESULTS

We identified no new studies with available results for this update. The earlier review included 20 studies (7238 participants) in valid comparisons, but because we used different outcomes for some headache studies, the number of participants in the analyses of the effects of caffeine is now 4262 when previously it was 5243. The studies were generally of good methodological quality, using standard designs and mostly standard scales of pain measurement, although many of those treating postoperative pain were small.Most studies used paracetamol or ibuprofen, with 100 mg to 130 mg caffeine, and the most common pain conditions studied were postoperative dental pain, postpartum pain, and headache. There was a small but statistically significant benefit with caffeine used at doses of 100 mg or more, which was not dependent on the pain condition or type of analgesic. About 5% to 10% more participants achieve a good level of pain relief (at least 50% of the maximum over four to six hours) with the addition of caffeine, giving a NNT of about 14 (high quality evidence).Most comparisons individually demonstrated numerical superiority with caffeine, but not statistical superiority. One serious adverse event was reported with caffeine, but was considered unrelated to any study medication.We know of the existence of around 25 additional studies with almost 12,500 participants for which data for analysis were not obtainable. The additional analgesic effect of caffeine remained statistically significant but clinically less important even if all the known missing data had no effect; the bulk of the unobtainable data are reported to have similar results as this review.

AUTHORS' CONCLUSIONS

The addition of caffeine (≥ 100 mg) to a standard dose of commonly used analgesics provides a small but important increase in the proportion of participants who experience a good level of pain relief.

Expression and characterization of purinergic receptors in rat middle meningeal artery-potential role in migraine

The dura mater and its vasculature have for decades been central in the hypothesis of migraine and headache pathophysiology. Although recent studies have questioned the role of the vasculature as the primary cause, dural vessel physiology is still relevant in understanding the complex pathophysiology of migraine. The aim of the present study was to isolate the middle meningeal artery (MMA) from rodents and characterize their purinergic receptors using a sensitive wire myograph method and RT-PCR. The data presented herein suggest that blood flow through the MMA is, at least in part, regulated by purinergic receptors. P2X1 and P2Y6 receptors are the strongest contractile receptors and, surprisingly, ADPβS caused contraction most likely via P2Y1 or P2Y13 receptors, which is not observed in other arteries. Adenosine addition, however, caused relaxation of the MMA. The adenosine relaxation could be inhibited by SCH58261 (A2A receptor antagonist) and caffeine (adenosine receptor antagonist). This gives one putative molecular mechanism for the effect of caffeine, often used as an adjuvant remedy of cranial pain. Semi-quantitative RT-PCR expression data for the receptors correlate well with the functional findings. Together these observations could be used as targets for future understanding of the in vivo role of purinergic receptors in the MMA.

Antinociceptive activity of methanolic extract of Muntingia calabura leaves: further elucidation of the possible mechanisms

Background

Muntingia calabura (Elaecoparceae) is a medicinal plant traditionally used, particularly, by the Peruvian people to alleviate headache and cold, pain associated with gastric ulcers or to reduce the prostate gland swelling. Following the recent establishment of antinociceptive activity of M. calabura leaf, the present study was performed to further elucidate on the possible mechanisms of antinociception involved.

Methods

The methanol extract of M. calabura (MEMC) was prepared in the doses of 100, 250 and 500 mg/kg. The role of bradykinin, protein kinase C, pottasium channels, and various opioid and non-opioid receptors in modulating the extract’s antinociceptive activity was determined using several antinociceptive assays. Results are presented as Mean ± standard error of mean (SEM). The one-way ANOVA test with Dunnett's multiple comparison was used to analyze and compare the data, with P < 0.05 as the limit of significance.

Results

The MEMC, at all doses, demonstrated a significant (p < 0.05) dose-dependent antinociceptive activity in both the bradykinin- and phorbol 12-myristate 13-acetate (PMA)-induced nociception. Pretreatment of the 500 mg/kg MEMC with 10 mg/kg glibenclamide (an ATP-sensitive K⁺ channel inhibitor), the antagonist of μ-, δ- and κ-opioid receptors (namely 10 mg/kg β-funaltrexamine, 1 mg/kg naltrindole and 1 mg/kg nor-binaltorphimine), and the non-opioid receptor antagonists (namely 3 mg/kg caffeine (a non-selective adenosinergic receptor antagonist), 0.15 mg/kg yohimbine (an α₂-noradrenergic antagonist), and 1 mg/kg pindolol (a β-adrenoceptor antagonist)) significantly (p < 0.05) reversed the MEMC antinociception. However, 10 mg/kg atropine (a non-selective cholinergic receptor antagonist), 0.15 mg/kg prazosin (an α₁-noradrenergic antagonist) and 20 mg/kg haloperidol (a non-selective dopaminergic antagonist) did not affect the extract's antinociception. The phytochemicals screening revealed the presence of saponins, flavonoids, tannins and triterpenes while the HPLC analysis showed the presence of flavonoid-based compounds.

Conclusions

The antinociceptive activity of MEMC involved activation of the non-selective opioid (particularly the μ-, δ- and κ-opioid) and non-opioid (particularly adenosinergic, α₂-noradrenergic, and β-adrenergic) receptors, modulation of the ATP-sensitive K⁺ channel, and inhibition of bradikinin and protein kinase C actions. The discrepancies in MEMC antinociception could be due to the presence of various phytochemicals.

Chronic pain epidemiology - where do lifestyle factors fit in?

Chronic pain is common and complex and has a large impact on individuals and society. Good epidemiological pain data provide key information on the use of resources (both in general practice and in specialist clinics), insight into factors that lead to or favour chronicity and the design of interventions aimed at reducing or preventing the effects of chronic pain. This review aims to highlight the important factors associated with chronic pain, including those factors which are amenable to lifestyle intervention.

Caffeine at Moderate Doses Can Inhibit Acupuncture-Induced Analgesia in a Mouse Model of Postoperative Pain

BACKGROUND

The use of acupuncture in the treatment of pain conditions has been extensively investigated. However, the influence of dietary ingredients on acupuncture-induced analgesia (AA) remains unexplored. Recently, the role of adenosine receptors in AA has been shown, and caffeine, one of the world's most commonly consumed dietary ingredients, is an antagonist of these receptors. In this study, the postincisional pain model was used to investigate caffeine's influence on AA.

METHOD

Mice submitted to plantar incision surgery were treated with acupuncture needling after administration of acute or chronic caffeine. Acupuncture needling was performed using two different types of stimuli, manual acupuncture and electroacupuncture bilaterally in the acupoint SP6.

RESULTS

We found that acute preadministration of caffeine (10 mg/kg, i.p.) completely reversed AA in both types of acupuncture. In the chronic preadministration, we used two doses that mimicked the average daily caffeine consumption in Western countries and China. Interestingly, the Western dose of caffeine (70 mg/kg/day) administered during 8 days in the drinking water reversed AA and the Chinese dose (4 mg/kg/day) administered during the same period did not.

CONCLUSIONS

These results indicate that the use of caffeine can inhibit the analgesic effect of different forms of acupuncture. In addition, our findings suggest that doses of caffeine relevant to dietary human intake levels could be a confounding factor in the context of acupuncture research.

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.

Purine receptor mediated actin cytoskeleton remodeling of human fibroblasts

Earlier studies have shown that activation of adenosine A1 receptors on peripheral pain fibers contributes to acupuncture-induced suppression of painful input. In addition to adenosine, acupuncture triggers the release of other purines, including ATP and ADP that may bind to purine receptors on nearby fibroblasts. We here show that purine agonists trigger increase in cytosolic Ca(2+) signaling in a cultured human fibroblasts cell line. The profile of agonist-induced Ca(2+) increases indicates that the cells express functional P2yR2 and P2yR4 receptors, as well as P2yR1 and P2xR7 receptors. Unexpectedly, purine-induced Ca(2+) signaling was associated with a remodeling of the actin cytoskeleton. ATP induced a transient loss in F-actin stress fiber. The changes of actin cytoskeleton occurred slowly and peaked at 10min after agonist exposure. Inhibition of ATP-induced increases in Ca(2+) by cyclopiazonic acid blocked receptor-mediated cytoskeleton remodeling. The Ca(2+) ionophore failed to induce cytoskeletal remodeling despite triggering robust increases in cytosolic Ca(2+). These observations indicate that purine signaling induces transient changes in fibroblast cytoarchitecture that could be related to the beneficial effects of acupuncture.

Methods for studying naturally occurring human pain and their analogues

Methods for investigating human pain have been developed over the last 100years. Typically, researchers focus on people with clinical pain, or on healthy participants undergoing laboratory-controlled pain-induction techniques focussed mostly on exogenously generated skin nociception. Less commonly investigated are acute pain experiences that emerge naturally. Six common painful complaints were identified: headache, muscular pain, visceral pain, menstrual pain, dental pain, and pain associated with upper respiratory tract infection. Methods used to recruit participants with the natural occurrence of each pain complaint were identified, and features of their use reviewed. Also reviewed were experimental analogues designed to mimic these pains, with the exception of menstrual pain. Headache and menstrual pain appear to be most effectively researched in their naturally occurring form, whereas muscle and dental pain may be more easily induced. Upper respiratory tract infection and abdominal pain provide further challenges for researchers. Summary guidance is offered, and directions for methods development outlined.

A Preliminary Study on the Effects of Self-Reported Dietary Caffeine on Pain Experience and Postoperative Analgesia

BACKGROUND

Caffeine reduces the amount of analgesic medications necessary to provide postoperative pain (POP) relief and augments treatments for headaches and dental pain. Despite considerable evidence of its beneficial effects, little is understood about the role of dietary caffeine consumption on baseline pain sensitivity or POP following oral surgery.

METHOD

Baseline experimental pain testing (quantitative sensory testing [QST]) using four stimulus modalities was conducted on 30 healthy adults (53% females) before surgical extraction of four third molars. Self-reported caffeine ingestion was reported before QST, and on the day of surgery, preoperative and postoperative caffeine plasma concentrations (CPC) were measured by mass spectrometry. POP ratings were obtained at timed intervals.

RESULTS

In QST, compared to subjects who self-reported no caffeine intake, those who self-reported caffeine ingestion demonstrated a higher pain sensitivity, particularly, on ramp and hold sustained heat at 44°C and 46°C, as well as a lower heat pain threshold and tolerance (p=0.05). Differences approached significance (p=0.06) in POP between subjects with CPC above 300 ng/mL and those with CPC below 300 ng/mL. Specifically, those with >300 ng/mL CPC had a slightly lower POP (mean 2.43, range 0-5) compared to those with <300 ng/mL CPC whose POP ratings were slightly higher (mean 2.89) with a greater variability (range 0-9.5).

CONCLUSIONS

Self-reported, dietary caffeine intake was associated with higher QST ratings with lower threshold and tolerance particularly on heat pain modalities. External factors (i.e., analgesic dosage) may have played a role in the analgesic effects of caffeine on POP in oral surgery, especially in individuals with CPC exceeding 300 ng/mL who reported lower pain.

Spinal serotonin 5-HT7 and adenosine A1 receptors, as well as peripheral adenosine A1 receptors, are involved in antinociception by systemically administered amitriptyline

The present study explored a link between spinal 5-HT(7) and adenosine A(1) receptors in antinociception by systemic amitriptyline in normal and adenosine A(1) receptor knock-out mice using the 2% formalin test. In normal mice, antinociception by systemic amitriptyline 3mg/kg was blocked by intrathecal administration of the selective adenosine A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) 10 nmol. Blockade was also seen in adenosine A(1) receptor +/+ mice, but not in -/- mice lacking these receptors. In both normal and adenosine A(1) receptor +/+ mice, the selective 5-HT(7) receptor antagonist (2R)-1-[(3-hydroxyphenyl)sulfonyl]-2-[2-(4-methyl-1-piperidinyl)ethyl]pyrrolidine hydrochloride (SB269970) 3 μg blocked antinociception by systemic amitriptyline, but it did not prevent antinociception in adenosine A(1) receptor -/- mice. In normal mice, flinching was unaltered when the selective 5-HT(7) receptor agonist (2S)-(+)-5-(1,3,5-trimethylpyrazol-4-yl)-2-(dimethylamino)tetralin (AS-19) 20 μg was administered alone, but increased when co-administered intrathecally with DPCPX 10 nmol or SB269970 3 μg. Intrathecal AS-19 decreased flinching in adenosine A(1) receptor +/+ mice compared to -/- mice. Systemic amitriptyline appears to reduce nociception by activating spinal adenosine A(1) receptors secondarily to 5-HT(7) receptors. Spinal actions constitute only one aspect of antinociception by amitriptyline, as intraplantar DPCPX 10 nmol blocked antinociception by systemic amitriptyline in normal and adenosine A(1) receptor +/+, but not -/- mice. Adenosine A(1) receptor interactions are worthy of attention, as chronic oral caffeine (0.1, 0.3g/L, doses considered relevant to human intake levels) blocked antinociception by systemic amitriptyline in normal mice. In conclusion, adenosine A(1) receptors contribute to antinociception by systemic amitriptyline in both spinal and peripheral compartments.

Determination of the caffeine contents of various food items within the Austrian market and validation of a caffeine assessment tool (CAT)

The caffeine content of 124 products, including coffee, coffee-based beverages, energy drinks, tea, colas, yoghurt and chocolate, were determined using RP-HPLC with UV detection after solid-phase extraction. Highest concentrations of caffeine were found for coffee prepared from pads (755 mg l⁻¹) and regular filtered coffee (659 mg l⁻¹). The total caffeine content of coffee and chocolate-based beverages was between 15 mg l⁻¹ in chocolate milk and 448 mg l⁻¹ in canned ice coffee. For energy drinks the caffeine content varied in a range from 266 to 340 mg l⁻¹. Caffeine concentrations in tea and ice teas were between 13 and 183 mg l⁻¹. Coffee-flavoured yoghurts ranged from 33 to 48 mg kg⁻¹. The caffeine concentration in chocolate and chocolate bars was between 17 mg kg⁻¹ in whole milk chocolate and 551 mg kg⁻¹ in a chocolate with coffee filling. A caffeine assessment tool was developed and validated by a 3-day dietary record (r²= 0.817, p < 0.01) using these analytical data and caffeine saliva concentrations (r²= 0.427, p < 0.01).

Caffeine as an analgesic adjuvant for acute pain in adults

BACKGROUND

Caffeine has been added to common analgesics such as paracetamol, ibuprofen, and aspirin, in the belief that it enhances analgesic efficacy. Evidence to support this belief is limited and often based on invalid comparisons.

OBJECTIVES

To assess the relative efficacy in acute pain of a single dose of any analgesic plus caffeine against the same dose of analgesic alone.

SEARCH METHODS

We searched CENTRAL, MEDLINE, EMBASE, and the Oxford Pain Relief Database to January 2012, and also carried out Internet searches and contacted pharmaceutical companies known to have carried out trials that have not been published.

SELECTION CRITERIA

We included randomised, double-blind studies that compared a single dose of analgesic plus caffeine with the same dose of the analgesic alone in the treatment of acute pain.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed eligibility and quality of studies, and extracted data. Any disagreements or uncertainties were settled by discussion with a third review author. We sought any validated measure of analgesic efficacy, but particularly the number of participants experiencing at least 50% of the maximum possible pain relief over four to six hours, participants reporting a global evaluation of treatment of very good or excellent, or headache relief after two hours. We pooled comparable data to look for a statistically significant difference, and calculated numbers needed to treat to benefit (NNT) with caffeine. We also looked for any numerical superiority associated with the addition of caffeine, and information about any serious adverse events.

MAIN RESULTS

We identified 19 studies (7238 participants) in valid comparisons. Most studies used paracetamol or ibuprofen, with 100 mg to 130 mg caffeine, and the most common pain conditions studied were postoperative dental pain, postpartum pain, and headache. There was a small but statistically significant benefit with caffeine used at doses of 100 mg or more, which was not dependent on the pain condition or type of analgesic. About 5% to 10% more participants achieve a good level of pain relief (at least 50% of the maximum) with the addition of caffeine, giving a NNT of about 15.Most comparisons individually demonstrated numerical superiority with caffeine, but not statistical superiority. One serious adverse event was reported with caffeine, but was considered unrelated to any study medication.We know or suspect of the existence of 20 additional studies with 9785 participants for which data for analysis were not obtainable. The additional analgesic effect of caffeine remained statistically significant but clinically less important even if all the known missing data had no effect; that is not likely to be the case.

AUTHORS' CONCLUSIONS

The addition of caffeine (≥ 100 mg) to a standard dose of commonly used analgesics provides a small but important increase in the proportion of participants who experience a good level of pain relief.