Tropisetron blocks analgesic action of acetaminophen: a human pain model study

Because the mechanism underlying the analgesic action of acetaminophen remains unclear, we investigated the possible interaction of acetaminophen with central serotonergic pathways. The effects of acetaminophen, tropisetron, the combination of both drugs, and saline on pain perception and central sensitization in healthy volunteers were compared. Sixteen healthy volunteers were included in this randomized, double-blind, placebo-controlled crossover study. Intracutaneous electrical stimulation (46.1 ± 19.1 mA) induced acute pain (numeric rating scale, 6 of 10) and stable areas of hyperalgesia and allodynia. Pain intensities and areas of hyperalgesia and allodynia were regularly assessed before, during, and after a 15-min infusion of acetaminophen, tropisetron, the combination of both drugs, and saline. Acetaminophen concentrations were measured to rule out any pharmacokinetic interaction. Both acetaminophen and tropisetron led to decreased pain ratings as compared to saline. However, when acetaminophen and tropisetron were administered simultaneously, the pain ratings were not affected. There was no significant difference in the evolution of the hyperalgesic and allodynic areas during the study period between the study groups (P = .06 and P = .33, respectively). Acetaminophen serum levels were not significantly different when associated with tropisetron (P = .063), although we observed a trend toward lower acetaminophen concentrations when both drugs were concurrently administered. In summary, while the combination of acetaminophen and tropisetron showed no analgesic action, each drug administered alone led to decreased pain ratings as compared to saline.     

Levetiracetam Interacts Synergistically With Nonsteroidal Analgesics and Caffeine to Produce Antihyperalgesia in Rats

Levetiracetam is a novel anticonvulsant with antihyperalgesic efficacy in inflammatory pain. Nonsteroidal analgesics and caffeine, as analgesic adjuvant, are widely used against inflammatory pain. This study characterized the manner in which levetiracetam interacts with analgesics (ibuprofen, celecoxib, and paracetamol) and caffeine to suppress hyperalgesia in a model of localized inflammation. Rat paw inflammation was induced by intraplantar carrageenan (.1 mL, 1%). Hyperalgesia and antihyperalgesic effects of levetiracetam (orally), analgesics (orally), and caffeine (intraperitoneally) alone and 2-drug combinations of levetiracetam with analgesics or caffeine were examined by a modified paw pressure test. The type of interaction between components was determined by isobolographic analysis or by analysis of the log dose-response curves for drug combination and drugs alone. Levetiracetam (10–200 mg/kg), ibuprofen (12.5–100 mg/kg), celecoxib (3.75–30 mg/kg), paracetamol (50–200 mg/kg), caffeine (15–100 mg/kg), and 2-drug combinations of levetiracetam with analgesics/caffeine produced a significant, dose-dependent reduction of inflammatory hyperalgesia. Isobolographic analysis revealed that levetiracetam exerts a synergistic interaction with analgesics, with approximately 7-, 9-, and 11-fold reduction of doses of both drugs in combination of levetiracetam with paracetamol, celecoxib, and ibuprofen, respectively. Analysis of the log dose-response curves for levetiracetam (1–50 mg/kg) in the presence of caffeine (10 mg/kg) and levetiracetam applied alone also revealed a synergistic interaction. Levetiracetam's ED₅₀ in the presence of caffeine was reduced approximately 11-fold.     

High-dose tramadol in comparison to low-dose morphine for cancer pain relief.

Cancer pain treatment following the World Health Organization guidelines is effective and feasible. However, the evidence supporting the use of opioids for mild to moderate pain on the second step of the analgesic ladder is widely discussed. The present evaluation compares the efficacy and safety of high doses of oral tramadol (> or = 300 mg/d) with low doses of oral morphine (< or = 60 mg/d). Patients were included in this nonblinded and nonrandomized study if the combination of a nonopioid analgesic and up to 250 mg/d of oral tramadol was inadequate. 810 patients received oral tramadol for a total of 23,497 days, and 848 patients received oral morphine for a total of 24,695 days. The average dose of tramadol was 428 +/- 101 mg/d (range 300-600 mg/d); the average dose of morphine was 42 +/- 13 mg/d (range 10-60 mg/d). Additional nonopioid analgesics were given on more than 95% of days. Antiemetics, laxatives, neuroleptics, and steroids were prescribed significantly more frequently in the morphine group; the use of other adjuvants was similar in both groups. The mean pain intensity on a 0-100 numerical rating scale (NRS) was 27 +/- 21 (95% CI 26-29) in the tramadol and 26 +/- 20 (95% CI 24-27) in the morphine group (NS). The analgesic efficacy was good in 74% and 78%, satisfactory in 10% and 7%, and inadequate in 16% and 15% of patients receiving tramadol and morphine, respectively (NS). Constipation, neuropsychological symptoms, and pruritus were observed significantly more frequently with low-dose morphine; other symptoms had similar frequencies in both groups. These data suggest that tramadol can be used for the treatment of cancer pain, when nonopioids alone are not effective. High doses of tramadol are effective and safe.     

Combination analgesic efficacy: individual patient data meta-analysis of single-dose oral tramadol plus acetaminophen in acute postoperative pain

The primary aims of this study were to assess the analgesic efficacy and adverse effects of single-dose oral tramadol plus acetaminophen in acute postoperative pain and to use meta-analysis to demonstrate the efficacy of the combination drug compared with its components. Individual patient data from seven randomized, double blind, placebo controlled trials of tramadol plus acetaminophen were supplied for analysis by the R.W. Johnson Pharmaceutical Research Institute, Raritan, New Jersey, USA. All trials used identical methods and assessed single-dose oral tramadol (75 mg or 112.5 mg) plus acetaminophen (650 mg or 975 mg) in adult patients with moderate or severe postoperative pain. Summed pain intensity and pain relief data over six and eight hours and global evaluations of treatment effect after eight hours were extracted. Number-needed-to-treat (NNT) for one patient to obtain at least 50% pain relief was calculated. NNTs derived from pain relief data were compared with those derived from pain intensity data and global evaluations. Information on adverse effects was collected. Combination analgesics (tramadol plus acetaminophen) had significantly lower (better) NNTs than the components alone, and comparable efficacy to ibuprofen 400 mg. This could be shown for dental but not postsurgical pain, because more patients were available for the former. Adverse effects were similar for the combination drugs and the opioid component alone. Common adverse effects were dizziness, drowsiness, nausea, vomiting, and headache. In sum, this meta-analysis demonstrated analgesic superiority of the combination drug over its components, without additional toxicity.     

Different profiles of buprenorphine-induced analgesia and antihyperalgesia in a human pain model

Different mechanisms were proposed for opioid-induced analgesia and antihyperalgesia, which might result in different pharmacodynamics. To address this issue, the time course of analgesic and antihyperalgesic effects of intravenous (i.v.) and sublingual (s.l.) buprenorphine was assessed in an experimental human pain model. Fifteen volunteers were enrolled in this randomized, double-blind, and placebo controlled cross-over study. The magnitude of pain and the area of secondary hyperalgesia following transcutaneous stimulation were repetitively assessed before and up to 150 min after administration of (1) 0.15 mg buprenorphine i.v. and placebo pill s.l., (2) 0.2 mg buprenorphine s.l. and saline 0.9% i.v. or (3) saline 0.9% i.v. and placebo pill s.l. as a control. The sessions were separated by 2 week wash-out periods. For both applications of buprenorphine the antihyperalgesic effects were more pronounced as compared to the analgesic effects (66+/-9 vs. 26+/-5% and 43+/-10 vs. 10+/-6%, for i.v. and s.l. application, respectively). This contrasts the pattern for the intravenous administration of pure mu-receptor agonists in the same model in which the antihyperalgesic effects are weaker. The apparent bioavailability of buprenorphine s.l. as compared to buprenorphine i.v. was 58% with a 15.8 min later onset of antinociceptive effects. The half-life of buprenorphine-induced analgesic and antihyperalgesic effects were 171 and 288 min, respectively. In contrast to pure mu-receptor agonists, buprenorphine exerts a lasting antihyperalgesic effect in our model. It will be of major clinical interest whether this difference will translate into improved treatment of pain states dominated by central sensitization.     

Tramadol/acetaminophen combination tablets for the treatment of osteoarthritis flare pain: a multicenter, outpatient, randomized, double-blind, placebo-controlled, parallel-group, add-on study

BACKGROUND: In a flare of osteoarthritis (OA) pain, increasing the dose of standard anti-inflammatory or routine analgesic drugs may not be practical because of an increased incidence of side effects. In patients achieving inadequate pain relief from traditional non-steroidal anti-inflammatory drugs (NSAIDs) or cyclooxygenase (COX)-2-selective inhibitors, it may be appropriate to add an analgesic agent with a different mechanism of action, thereby targeting multiple components of the pain pathway. OBJECTIVE: The addition of tramadol/acetaminophen tablets to existing therapy was compared with the addition of placebo in the treatment of OA flare pain. METHODS: This was a multicenter, outpatient, randomized, double-blind, placebo-controlled, parallel-group, add-on study. Patients received 1 or 2 tramadol/acetaminophen (37.5 mg/325 mg) tablets QID or matching placebo for 10 days in addition to ongoing NSAID or COX-2-selective inhibitor therapy. The primary outcome measures were average daily pain intensity and average daily pain relief scores from days 1 through 5. RESULTS: Three hundred eight patients were randomized to tramadoUacetaminophen (n = 197) or placebo (n = 111) and were followed for up to 10 days. Patients had a mean (+/-SD) age of 60.1 +/- 9.87 years, and were predominantly female (71.8%) and white (87.7%). Their mean (+/- SD) pain visual analog score at baseline was 73.2 +/- 11.8 mm, and their mean pain intensity score was 2.4 +/- 0.5 (on a scale from 0 = none to 3 = severe). Average daily pain intensity and pain relief scores were significantly improved with tramadol/acetaminophen compared with placebo on the primary assessment of efficacy from days 1 through 5 (both, P < 0.001) and on the assessment of efficacy from days I through 10 (both, P < 0.001) Tramadol/acetaminophen was significantly superior to placebo on the patients' and physicians' overall assessments of medication (both, P < 0.001) and on 3 of 4 subscales (pain [P = 0.004], physical function [P = 0.013], and overall [P = 0.008]) of the Western Ontario and McMaster Universities Osteoarthritis Index Questionnaire. The most common treatment-emergent adverse events with tramadol/acetaminophen were nausea, vomiting, and dizziness. No serious adverse events were reported in the tramadol/acetaminophen group. CONCLUSION: In this study, addition of tramadol/acetaminophen to NSAID or COX-2-selective inhibitor therapy was well tolerated and effective in the treatment of OA flare pain.     

Pharmacology of oral combination analgesics: rational therapy for pain

No single analgesic agent is perfect and no single analgesic can treat all types of pain. Yet each agent has distinct advantages and disadvantages compared to the others. Hence, clinical outcomes might be improved under certain conditions with the use of a combination of analgesics, rather than reliance on a single agent. A combination is most effective when the individual agents act through different analgesic mechanisms and act synergistically. By activating multiple pain-inhibitory pathways, combination analgesics can provide more effective pain relief for a broader spectrum of pain, and might also reduce adverse drug reactions. This overview highlights the therapeutic potential of combining analgesic medications with different mechanisms of action, particularly a nonsteroidal anti-inflammatory drug (NSAID) or acetaminophen with an opioid or tramadol.     

Hydrocodone/acetaminophen and tramadol chlorhydrate combination tablets for the management of chronic cancer pain: a double-blind comparative trial

OBJETIVES: The purpose of this study was to compare the analgesic efficacy and tolerability of opioids hydrocodone and tramadol in the relief of cancer pain. METHODS: One hundred and eighteen patients with chronic cancer pain participated in a double-blind, randomized controlled trial. Sixty-two patients received hydrocodone and 56 patients received tramadol. RESULTS: Hydrocodone/acetaminophen was effective in relieving pain in 56.5% of the patients at the starting dose of 25 mg/2500 mg/d. An additional 14.5% of the patients responded to a double dose, and the remaining 29% of patients did not experience any pain relief from hydrocodone administration. One dose of tramadol at 200 mg/d produced pain relief in 62% of the patients and alleviated pain in another 11% of patients at a dose of 400 mg/d, and remaining 27% of patients did not experience pain relief from tramadol. No significant statistical difference in the analgesic efficacy of tramadol clorhydrate and hydrocodone/acetaminophen was found. The groups differed significantly in the incidence of side effects like nausea (P=0.03; relative risk (RR), 1.69; confidence interval (IC) 95%, 1.03-2.77), vomiting (P=0.02; RR, 2.21; IC 95%, 1.14-4.32), dizziness (P=0.03; RR, 2.12; IC 95%, 1.17-3.86), loss of appetite (P=0.02; RR, 3.27; IC 95%, 1.12-9.55) and weakness (P=0.019; RR, 7.75; IC 95%, 0.98-61.05). CONCLUSIONS: There was no superior analgesic efficacy with the administration of hydrocodone/acetaminophen when compared to patients receiving tramadol in the relief of cancer pain. Tramadol produced more mild side effects than hydrocodone.     

Analgesic oral efficacy of tramadol hydrochloride in postoperative pain.

Tramadol hydrochloride is a synthetic opiate agonist with a plasma elimination half-life of 5 to 6 hours and peak plasma levels at about 1 1/2 hours. It derives its activity from attachment to the mu-receptor and blockage of norepinephrine reuptake. The purpose of this single-dose, double-blind, placebo-controlled study was to determine the analgesic effectiveness of an oral administration of two dose levels of tramadol hydrochloride (75 or 150 mg) compared with the combination of 650 mg acetaminophen plus 100 mg propoxyphene napsylate in 161 patients with severe postoperative pain after cesarean section. Analgesia was assessed over a 6-hour period. Treatments were compared on the basis of standard scales for pain intensity and relief and a number of derived variables based on these data. A global rating of the study medication was also used to compare treatments. The three active treatments were effective analgesics, statistically superior to placebo for many hourly and summary measures. A dose response was seen between the two tramadol doses, with the 150 mg dose providing significantly greater analgesia over the lower dose. The 75 mg dose of tramadol was generally more effective than the acetaminophen-propoxyphene combination after hour 2, and significantly so for some hourly time points, as well as for the global rating of the medication. The 150 mg dose of tramadol was significantly more effective than the acetaminophen-propoxyphene combination from hour 2 through hour 6 for the sum of pain intensity differences and total pain relief scores, as well as for the global rating of the medication. Tramadol hydrochloride at both dose levels is an effective analgesic agent and at 150 mg is statistically superior to the acetaminophen-propoxyphene combination. No serious adverse effects were observed; however, dizziness was more frequently reported with 150 mg tramadol.     

Combination hydrocodone and ibuprofen versus combination codeine and acetaminophen for the treatment of chronic pain

OBJECTIVE: The objective of this study was to compare the effectiveness of combination hydrocodone 7.5 mg and ibuprofen 200 mg with that of combination codeine 30 mg and acetaminophen 300 mg for the treatment of chronic pain. BACKGROUND: Hydrocodone 7.5 mg with ibuprofen 200 mg is the only approved fixed-dose combination analgesic containing an opioid and ibuprofen. METHODS: In this randomized, parallel-group, double-blind, repeated-dose, active-comparator, 4-week, multicenter study, 469 patients were randomly assigned to receive a 1-tablet (n = 156) or 2-tablet (n = 153) dose of combination hydrocodone 7.5 mg and ibuprofen 200 mg (HI1 and HI2, respectively) or a 2-tablet dose of combination codeine 30 mg and acetaminophen 300 mg (CA, n = 160), the active comparator, every 6 to 8 hours as needed for pain. Efficacy was measured through pain relief scores, number of daily doses of study medication, number of daily doses of supplemental analgesics, number of patients who discontinued therapy due to an unsatisfactory analgesic response, and global assessment scores. RESULTS: Of the 469 patients, 255 (54.4%) were female and 214 (45.6%) were male. The mean age was 51.1 years. Types of chronic pain included back (214; 45.6%), arthritic (145; 30.9%), other musculoskeletal (65; 13.9%), cancer (6; 1.3%), diabetic neuropathic (3; 0.6%), postherpetic neuralgic (5; 1.1%), other neurologic (21; 4.5%), and other unclassified chronic pain (10; 2.1%). During the 48 hours prior to the study, 351 (74.8%) patients had been treated with opioid or opioid-nonopioid combination analgesics. The overall mean daily pain relief score was significantly greater in the HI2 group (2.25+/-0.89) than in the HI1 group (1.98+/-0.87) (P = 0.003) or the CA group (1.85+/-0.96) (P < 0.001). The overall mean number of daily doses of study medication was significantly less in the HI2 group (2.94+/-0.99) than in the HI1 group (3.23+/-0.76) (P = 0.036) or the CA group (3.26+/-0.75) (P = 0.014). The overall mean number of daily doses of supplemental analgesics was significantly less in the HI2 group (0.24+/-0.49) than in the HI1 group (0.34+/-0.58) (P = 0.021) or CA group (0.49+/-0.85) (P = 0.010). The number of patients who discontinued treatment due to an unsatisfactory analgesic response was significantly less in the HI2 group (2; 1.3%) than in the CA group (12; 7.5%) (P = 0.008). HI2 was more effective than HI1 and CA as measured by pain relief scores for week 1 (P < 0.001 vs HI1 and CA), week 2 (P < 0.001 vs HI1 and CA), and week 3 (P = 0.008 vs HI1 and P < 0.001 vs CA); daily doses of study medication for week 1 (P = 0.019 vs HI1 and P = 0.011 vs CA); daily doses of supplemental analgesics for week 1 (P = 0.010 vs HI1 and CA); and global assessment scores for week 1 (P = 0.018 vs HI1 and P < 0.001 vs CA), week 2 (P = 0.005 vs HI1 and P < 0.001 vs CA), and week 4 (P = 0.013 vs HI1 and P = 0.023 vs CA). There were no significant differences between HI1 and CA in any efficacy variable. There were no significant differences in the number of patients experiencing adverse events in the HI2 (127; 83%), HI1 (124; 79.5%), and CA (129; 80.6%) groups. However, the mean number of patients who discontinued treatment due to adverse events was significantly greater in the HI2 group (40; 26.1%) than in the HI1 group (23; 14.7%) (P = 0.013). CONCLUSIONS: The results of this study suggest that 2-tablet doses of combination hydrocodone 7.5 mg and ibuprofen 200 mg may be more effective than either 1-tablet doses of this combination or 2-tablet doses of combination codeine 30 mg and acetaminophen 300 mg. Moreover, 1-tablet doses of combination hydrocodone 7.5 mg and ibuprofen 200 mg may be as effective as 2-tablet doses of combination codeine 30 mg and acetaminophen 300 mg.     

Postoperative pain relief with pentazocine and acetaminophen: comparison with other analgesic combinations and placebo

A single-blind, parallel-group study was carried out to evaluate the efficacy and safety of an analgesic combining 650 mg of acetaminophen and 25 mg of pentazocine in 129 patients with moderate postoperative pain. Comparisons were made with a combination containing acetaminophen (300 mg) and codeine (30 mg), a combination containing acetaminophen (650 mg) and propoxyphene napsylate (100 mg), and a placebo. A nurse observer queried patients at regular intervals over a six-hour period concerning the intensity of pain and the degree of pain relief. The scores obtained were used in the calculation of standard measures of analgesic efficacy. Acetaminophen/pentazocine proved to be significantly superior to placebo and equivalent to the other active analgesic combinations. No side effects were reported with acetaminophen/pentazocine, acetaminophen/propoxyphene napsylate, or placebo. One mild side effect was questionably associated with acetaminophen/codeine. This study demonstrates that the combination of acetaminophen and pentazocine is as safe and effective in controlling postoperative pain of moderate severity as other commonly used analgesics.     

Antinociceptive and antihyperalgesic effects of tapentadol in animal models of inflammatory pain

The novel analgesic tapentadol HCl [(-)-(1R,2R)-3-(3-dimethylamino)-1-ethyl-2-methyl-propyl)-phenol hydrochloride] combines μ-opioid receptor (MOR) agonism and noradrenaline reuptake inhibition (NRI) in a single molecule and shows a broad efficacy profile in various preclinical pain models. This study analyzed the analgesic activity of tapentadol in experimental inflammatory pain. Analgesia was evaluated in the formalin test (pain behavior, rat and mouse), carrageenan-induced mechanical hyperalgesia (paw-pressure test, rat), complete Freund's adjuvant (CFA)-induced paw inflammation (tactile hyperalgesia, rat), and CFA knee-joint arthritis (weight bearing, rat). Tapentadol showed antinociceptive activity in the rat and mouse formalin test with an efficacy of 88 and 86% and ED(50) values of 9.7 and 11.3 mg/kg i.p., respectively. Tapentadol reduced mechanical hyperalgesia in carrageenan-induced acute inflammatory pain by 84% with an ED(50) of 1.9 mg/kg i.v. In CFA-induced tactile hyperalgesia, tapentadol showed 71% efficacy with an ED(50) of 9.8 mg/kg i.p. The decrease in weight bearing after CFA injection in one knee joint was reversed by tapentadol by 51% with an ED(25) of 0.9 mg/kg i.v. Antagonism studies were performed with the MOR antagonist naloxone and the α(2)-noradrenergic receptor antagonist yohimbine in the carrageenan- and CFA-induced hyperalgesia model. In the CFA model, the serotonergic receptor antagonist ritanserin was also tested. The effect of tapentadol was partially blocked by naloxone and yohimbine and completely blocked by the combination of both, but it was not affected by ritanserin. In summary, tapentadol showed antinococeptive/antihyperalgesic analgesic activity in each model of acute and chronic inflammatory pain, and the antagonism experiments suggest that both MOR activation and NRI contribute to its analgesic effects.     

Dose response of tramadol and its combination with paracetamol in UVB induced hyperalgesia

Combining tramadol with paracetamol is an established analgesic treatment strategy. However, dosing and differential effects on peripheral and central hyperalgesia are still to be determined. After Ethics Committee approval, 32 volunteers have been included in this 2 phased, double blinded, placebo controlled, cross‐over study. A defined small skin area was irradiated with a UVB source inducing hyperalgesia. Twenty‐four hours after irradiation, heat pain‐, cold pain threshold (HPPT, CPPT), mechanical pain sensitivity to pin prick (MPS) in the area of pin prick hyperalgesia (AsH) and MPS in the sunburn were determined. In phase I, measurements have been repeated 30 min after receiving cumulative 0.3, 0.6 and 1 mg/kg of intravenous (i.v.) tramadol or active placebo. Only at 1 mg/kg tramadol and solely for MPS in the sunburn a reduction to placebo could be demonstrated (p = 0.024). Accordingly in phase II, the trial has been repeated using 1 mg/kg tramadol and paracetamol or placebo in a cumulative i.v. dose of 330, 660 and 990 mg. Now the addition of 330 mg paracetamol to tramadol reduced thermal hyperalgesia by 1.15 °C (CI 0.55; 1.76). This effect, however, did not increase with higher doses. Tramadol showed week anti‐hyperalgesia reducing CPPT, MPS and AsH compared to baseline measurements (p < 0.05). Paracetamol also reduced secondary hyperalgesia, but no combination effect with tramadol could be shown. We conclude, in inflammatory hyperalgesia tramadol alone exerts only weak anti‐hyperalgesia. Even adding a small dose paracetamol enhances thermal anti‐hyperalgesia.     

Double blind comparison of mefenamic acid and acetaminophen (paracetamol) in migraine

We have assessed the role of mefenamic acid, a non-steroidal anti-inflammatory drug known to inhibit both the synthesis and actions of prostaglandins, as an analgesic in migraine by comparing it with the established analgesic paracetamol (acetaminophen) in a double-blind cross-over trial. Forty ambulant migraine patients were supplied with oral medication for six consecutive attacks; metoclopramide 10 mg was administered in all attacks, and paracetamol 500 mg and mefenamic acid 500 mg for three attacks each. The patients recorded the intensity of the headache at the time the medication was taken, and again after 3 hours, on a linear analogue scale. Twenty-two patients completed the trial satisfactorily. Seven had insufficient attacks and the remainder were lost to follow-up. The mean reduction in headache intensity was 36 +/- 11% on mefenamic acid and 27 +/- 10% (both mean +/- SEM) on paracetamol. While this difference is not quite statistically significant (0.1 greater than P greater than 0.05) there still remains a 28% probability that mefenamic acid is twice as potent as an analgesic. The responses in each individual patient to the two drugs were very closely correlated (P much less than 0.001). Our failure to demonstrate a convincing difference between the two analgesics leads us to speculate that peripheral prostaglandin mediated pain pathways, in which paracetamol is inactive, may be less important than central pathways, which are inhibited by both drugs.     

Antihyperalgesic and analgesic properties of the N‐methyl‐d‐aspartate (NMDA) receptor antagonist neramexane in a human surrogate model of neurogenic hyperalgesia

NMDA‐receptors are a major target in the prevention and treatment of hyperalgesic pain states in neuropathic pain. However, previous studies revealed equivocal results depending on study design and efficacy parameters. We tested the analgesic (generalized reduction of generation and processing of nociceptive signalling) and anti‐hyperalgesic (prevention of central sensitization) properties of the NMDA‐receptor antagonist neramexane and the potassium channel opener flupirtine in the intradermal capsaicin injection model. Furthermore, we tested the effect on pain summation (wind up). Eighteen healthy subjects received either a single dose of neramexane (40mg p.o.), flupirtine (100mg) or placebo in a double‐blind, randomized, cross‐over study. Pain evoked by intradermal capsaicin injection as well as pain evoked by pinpricks was significantly reduced by neramexane (?22% to ?30% vs. placebo) in the non‐sensitized skin indicating a marked analgesic effect. Moreover, dynamic mechanical allodynia (pain to light touch) was also significantly attenuated by neramexane (?28% vs. placebo). However, static secondary hyperalgesia to pinprick stimuli after capsaicin injection was not significantly reduced (?9% vs. placebo). Flupirtine showed no analgesic or anti‐hyperalgesic effect. Mechanically‐evoked wind up of pain sensation was not affected by any treatment. The results suggests that in a human surrogate model of neurogenic hyperalgesia a single low‐dose of neramexane had a marked analgesic effect in the sensitized and in the non‐sensitized state and thus may be a useful drug to treat the enhanced pain sensitivity in neuropathic pain patients. Its efficacy may be based on analgesia rather than anti‐hyperalgesia or anti‐windup. In contrast, flupirtine showed neither an analgesic nor an anti‐hyperalgesic effect at a dose used for the treatment of postoperative pain.     

Comparison of Oral Ibuprofen and Acetaminophen with Either Analgesic Alone for Pediatric Emergency Department Patients with Acute Pain

BackgroundIbuprofen (Motrin; Johnson & Johnson) and acetaminophen (APAP, paracetamol) are the most commonly used analgesics in the pediatric emergency department (ED) for managing a variety of acute traumatic and nontraumatic painful conditions. The multimodal pain management of using a combination of ibuprofen plus acetaminophen has the potential to result in greater analgesia.ObjectiveWe compared the analgesic efficacy of a combination of oral ibuprofen plus acetaminophen with either analgesic alone for pediatric ED patients with acute pain.MethodsWe performed a randomized, double-blind superiority trial assessing and comparing the analgesic efficacy of a combination of oral ibuprofen (10 mg/kg dose) plus acetaminophen (15 mg/kg per dose) to either analgesic alone for the treatment of acute traumatic and nontraumatic pain in the pediatric ED. Primary outcomes included a difference in pain scores among the three groups at 60 min.ResultsWe enrolled 90 patients (30 per group). The difference in mean pain scores at 60 min between acetaminophen and combination groups was 0.30 (95% confidence interval [CI] −0.84 to 1.83); between ibuprofen and combination groups was −0.33 (95% CI −1.47 to 0.80); and between acetaminophen and ibuprofen groups was 0.63 (95% CI −0.54 to 1.81). Reductions in pain scores from baseline to 60 min were similar for all patients in each of the three groups. No adverse events occurred in any group.ConclusionsWe found similar analgesic efficacy of oral ibuprofen and acetaminophen in comparison with each analgesic alone for short-term treatment of acute pain in the pediatric ED, but the trial was underpowered to demonstrate the analgesic superiority of the combination of oral ibuprofen plus acetaminophen in comparison with each analgesic alone.     

Spinal inflammatory hyperalgesia is mediated by prostaglandin E receptors of the EP2 subtype

Blockade of prostaglandin (PG) production by COX inhibitors is the treatment of choice for inflammatory pain but is also prone to severe side effects. Identification of signaling elements downstream of COX inhibition, particularly of PG receptor subtypes responsible for pain sensitization (hyperalgesia), provides a strategy for better-tolerated analgesics. Here, we have identified PGE2 receptors of the EP2 receptor subtype as key signaling elements in spinal inflammatory hyperalgesia. Mice deficient in EP2 receptors (EP2-/- mice) completely lack spinal PGE2-evoked hyperalgesia. After a peripheral inflammatory stimulus, EP2-/- mice exhibit only short-lasting peripheral hyperalgesia but lack a second sustained hyperalgesic phase of spinal origin. Electrophysiological recordings identify diminished synaptic inhibition of excitatory dorsal horn neurons as the dominant source of EP2 receptor-dependent hyperalgesia. Our results thus demonstrate that inflammatory hyperalgesia can be treated by targeting of a single PG receptor subtype and provide a rational basis for new analgesic strategies going beyond COX inhibition.     

Combination hydrocodone and ibuprofen versus combination oxycodone and acetaminophen in the treatment of moderate or severe acute low back pain

BACKGROUND: Introduced in 1997, the combination of hydrocodone and ibuprofen is the only fixed-dose combination analgesic containing an opioid and ibuprofen that has been approved by the US Food and Drug Administration. OBJECTIVE: This study compared the efficacy and tolerability of combination hydrocodone 7.5 mg and ibuprofen 200 mg (HC/IB) with those of combination oxycodone 5 mg and acetaminophen 325 mg (OX/AC) in the treatment of moderate or severe acute low back pain. METHODS: This was a multicenter, randomized, double-blind, parallel-group, repeat-dose study lasting up to 8 days. The recommended dosing of the study medications was 1 tablet every 4 to 6 hours, not to exceed 5 tablets per day. If adequate pain relief was not obtained, patients were permitted to take up to 4 doses per day of supplemental analgesic medication-the nonopioid component of the assigned study medication (ibuprofen 200 mg or acetaminophen 325 mg). Measures of efficacy included mean daily pain relief scores (0 = no relief, 1 = slight relief, 2 = moderate relief, 3 = good relief, and 4 = complete relief), mean daily number of tablets and doses of study medication, mean daily number of tablets and doses of supplemental analgesic medication, global evaluation (poor, fair, good, very good, or excellent), and results on the modified 36-item Short-Form Health Survey (SF-36). All efficacy measures were analyzed on an intent-to-treat basis. Tolerability was evaluated based on adverse events reported spontaneously or elicited by the in vestigators using nonsuggestive questioning, as well as on the number of patients discontinuing treatment because of adverse events. RESULTS: The study enrolled 147 patients (75 HC/IB, 72 OX/AC). The most common cause of low back pain was muscular/ligamentous injury (97/147; 66.0%), followed by degenerative disk disease (27/147; 18.4%). At baseline, 80 patients (54.4%) reported experiencing moderate pain, and 67 patients (45.6%) reported experiencing severe pain. There were no significant differences between HC/IB and OX/AC with regard to mean ( +/- SD) daily pain relief scores (2.40 +/- 1.06 vs 2.50 +/- 1.01, respectively), mean daily number of tablets of study medication (1.80 +/- 1.70 vs 2.20 +/- 1.60), mean daily number of doses of study medication (1.80 +/- 1.65 vs 2.10 +/- 1.58), mean daily number of tablets of supplemental analgesic medication (0.60 +/- 1.13 vs 0.50 +/- 0.99), mean daily number of doses of supplemental analgesic medication (0.60 +/- 1.07 vs 0.50 +/- 0.90), global evaluations, or mean scores on the modified SF-36. In addition, there were no significant differences in the proportion of patients experiencing adverse events with HC/IB (47; 62.7%) and OX/AC (45; 62.5%). Adverse events were consistent with those generally associated with the component analgesics and predominantly involved the central nervous system and gastrointestinal system. CONCLUSIONS: The results of this study suggest that HC/IB and OX/AC are similarly effective and tolerable in relieving moderate or severe acute low back pain. Additional controlled longitudinal trials are necessary to evaluate the clinical utility of HC/IB in treating acute low back pain.     

Low-dose lidocaine reduces secondary hyperalgesia by a central mode of action

Sodium channel blockers are approved for intravenous administration in the treatment of neuropathic pain states. Preclinical studies have suggested antihyperalgesic effects on the peripheral as well as the central nervous system. The objective of this study was to determine mechanisms of action of low-dose lidocaine in experimental induced, secondary hyperalgesia. In a first experimental trial, participants (n=12) received lidocaine systemically (a bolus injection of 2 mg/kg in 10 min followed by an intravenous infusion of 2 mg kg(-1)h(-1) for another 50 min). In a second trial, a modified intravenous regional anesthesia (IVRA) was administered to exclude possible central analgesic effects. In one arm, patients received an infusion of 40 ml lidocaine, 0.05%; in the other arm 40 ml NaCl, 0.9%, served as a control. In both trials capsaicin, 20 microgram, was injected intradermally and time course of capsaicin-induced pain, allodynia and hyperalgesia as well as axon reflex flare was determined. The capsaicin-induced pain was slightly reduced after systemic and regional application of the anesthetic. The area of pin-prick hyperalgesia was significantly reduced by systemic lidocaine, whereas the inhibition of hyperalgesia was absent during regional administration of lidocaine. In contrast, capsaicin-induced flare was significantly decreased after both treatments. We conclude that systemic lidocaine reduces pin-prick hyperalgesia by a central mode of action, which could involve blockade of terminal branches of nociceptors. A possible role for tetrodotoxin resistant sodium channels in the antihyperalgesic effect of low-dose lidocaine is discussed.     

Tramadol/acetaminophen combination tablets and codeine/acetaminophen combination capsules for the management of chronic pain: a comparative trial

BACKGROUND: Opioid/acetaminophen (APAP) combination analgesics are widely prescribed for the relief of moderate pain. Tramadol is a synthetic analgesic that has been shown to be effective both alone and in combination with APAP. OBJECTIVE: The purpose of this study was to compare the efficacy and tolerability of tramadol/APAP tablets with codeine/APAP capsules. METHODS: This 4-week, randomized, double-blind, parallel-group, active-control, double-dummy, multicenter trial compared tramadol/APAP (37.5 mg/325 mg) with codeine/APAP (30 mg/300 mg) for the management of chronic nonmalignant low back pain, osteoarthritis (OA) pain, or both in adults. Pain relief (scale, 0 = none to 4 = complete) and pain intensity (scale, 0 = none to 3 = severe) were measured 30 minutes and then hourly for 6 hours after the first daily dose each week. Patients and investigators assessed the efficacy (scale, 1 = poor to 5 = excellent) of each medication, and patients recorded daily doses of study and rescue medications. RESULTS: A total of 462 patients (mean age, 57.6 years) were randomly assigned to treatment, with 112 (24%) reporting chronic low back pain, 162 (35%) reporting OA pain, and 188 (41%) reporting both low back and OA pain; 309 patients (67%) received tramadol/APAP and 153 (33%) received codeine/APAP. Pain relief and changes in pain intensity were comparable from day 1, as early as 30 minutes after the first dose, and lasted for at least 6 hours. Total pain relief scores (11.9 for tramadol/APAP; 11.4 for codeine/APAP) and sum of pain intensity differences (3.8 for tramadol/APAP; 3.3 for codeine/APAP) were also comparable throughout. Overall assessments of efficacy by patients (mean score 2.9 in each treatment group) and investigators (mean score 3.0 for tramadol/APAP, 2.9 for codeine/APAP) were similar for the 2 treatment groups. Equivalent mean doses (3.5 tablets or capsules daily) and maximum daily doses (5.5 tablets or 5.7 capsules) were used in the 2 treatment groups. The overall incidence of adverse events was comparable, with a significantly higher proportion of patients in the codeine/APAP group reporting somnolence (24% [37/153] vs 17% [54/309], P = 0.05) or constipation (21% [32/153] vs 11% [35/309], P < 0.01) and a larger proportion of patients in the tramadol/APAP group reporting headache (11% [34/309] vs 7% [11/153], P = 0.08). CONCLUSION: The results of this study suggest that tramadol/APAP tablets (37.5 mg/325 mg) are as effective as codeine/ APAP capsules (30 mg/300 mg) in the treatment of chronic nonmalignant low back pain and OA pain and are better tolerated.