Lombalgia: qual o melhor tratamento? Medicação x Atividade Física
Low back pain is a common health problem and the leading cause of disability worldwide.1,2 While management guidelines encourage the prescription of simple analgesics for low back pain (eg, paracetamol or nonsteroidal antiinflammatory drugs [NSAIDs]),many people with low back pain are prescribed opioid analgesics.3,4 Findings from the United States show that more than half of the people regularly treated with prescription opioid analgesics have chronic low back pain.4 Similarly in Australia the 3most commonly prescribed drugs for back pain are opioid analgesics or opioid analgesic combinations: oxycodone (11.7%), tramadol (8.2%), and paracetamol and codeine combination (12.1%) (percent of all prescribed medicines for back pain).5,6 Despite the widespread use of opioid analgesics for people with low back pain, there remains uncertainty about 3 central issues that would guide rational prescribing of these medicines for the treatment of people with low back pain. Two recent high-quality systematic reviews have shown that, because of a lack of trials, there isuncertainty regarding the efficacy of opioid analgesics for people with acute low back pain7 and also when these medicines are used long term for chronic low back pain.8There is also uncertainty regarding the optimal dosing of opioid analgesics because, to our knowledge, there has been no systematic evaluation of how the dose of these medicines may influence the size of any treatment effect for people with low back pain.9-14 Finally, there has been little consideration of the extent to which an unselected group of opioidnaïve people with low back pain would tolerate or respond to an opioidmedicine. For example,many opioid trials use an enrichment study design and exclude participants who do not tolerate or adequately respond to the opioid analgesic in the run-in phase. Some trials also exclude participants who do not respond to or tolerate the opioid analgesic in the randomizedphase of a trial, and therefore the estimate of treatment efficacy is derived from only a proportion of participants who were enrolled in the study to receive opioid analgesics. The aims of this systematic review were to (1) evaluate the efficacy of opioid analgesics in the management of low back pain, (2) investigate the effect of opioid dose and enrichment study design on treatment effect, and (3) quantify treatment discontinuation (owing to adverse events and lack of efficacy) and loss to follow-up in the run-in and randomized phases of trials.
Results A total of 20 trials of opioid analgesics (a total of 7295 participants) were included in this review (see Table). Nineteen opioid analgesic trials evaluated participantswith chronic low back pain, and 1 head-to-head trial evaluated participants with subacute low back pain. Seventeen RCTs compared an opioid analgesic with placebo and 3 trials compared 2 opioid analgesics.29-31 None of the trials evaluated long-term use or outcomes, the maximum treatment period was 12 weeks, and the maximum follow-up was also 12 weeks. Seventeen of the 20 trials reported industry funding. The medicines used in these trials were oral hydromorphone,32 oxymorphone,29,33,34 morphine,30,35 tramadol monotherapy31,36-38 or in combination with paracetamol,31,39-41 tapentadol,42 oxycodone monotherapy,42-44 oxycodone in combination with naloxone,45 or naltrexone,44 transdermal buprenorphine,43,46,47 transdermal fentanyl,30 and hydrocodone.48 The trials were typically of high quality with a mean (SD) PEDro score of 7.8 (1.5). The PEDro ratings are summarized in eTable 2 in the Supplement. Treatment Efficacy: Pain and Disability Outcomes Pain Outcomes There is moderate-quality evidence from 13 studies of chronic low back pain (3419 participants) of an effect of singleingredient opioid analgesics on pain in the short term;mean difference (MD), −10.1 (95% CI, −12.8 to −7.4) (Figure 2). There is high-quality evidence from 6 studies (2605 participants) that single-ingredient opioid analgesics relieve pain in the intermediate term; MD, −8.1 (95% CI, −10.2 to −6.0). Combination opioid analgesics containing a simple analgesic showed moderate evidence of pain relief in the intermediate term;MD, −11.9 (95% CI, −19.3 to −4.4). Results from a single trial of the combination of tramadol/paracetamol provided very low quality evidence of pain relief for the short term; MD, −8 (95% CI, −16.2 to 0.2).41 The effects of single-ingredient and combination opioids were minimal and approximately half the 20-point threshold for clinical importance. A funnel plot of standard error by treatment effect for the short and intermediate term is shown in eFigures 1 and 2 in the Supplement, respectively. The evidence for shortterm efficacy was downgraded 1 level for publication bias (Egger P= .007). There were no long-term outcomes data. Disability Outcomes There were limited data on disability outcomes. Results from a single trial showed no significant effect of the combination of tramadol-paracetamol41on disability for the short term;MD, −6.2 (95% CI, −8.5 to 20.9), and results from another single trial40 of the tramadol-paracetamol combination showed no significant effect for the intermediate term; MD, −3.7 (−11.8 to 4.4). The evidence from these trials is of very low quality. A single study of morphine35 showed no clinically significant reduction in disability for the short term; MD, −6.3 (95% CI, 0.5-12.1), with the evidence being of very low quality. See eTable 4 in the Supplement for overall grading of evidence and eTable 5 in the Supplement for morphine equivalent conversions. Effect of Opioid Dose and Enrichment Study Design on Short-Term Treatment Efficacy In the 13 RCTs evaluating short-term efficacy, the morphineequivalent dose ranged from 40.0 mg to 242.7 mg per day. Seven of the 13 RCTs used an enrichment study design whereby only the participants who responded favorably to the study medication, and tolerated themedicine in the trial run-in phase (prerandomization) were eligible to continue in the trial proper and be randomized to the study treatment. Trial results grouped by log opioid dose and enrichment study design are shown inFigure 3A and B, respectively. Results from the stratified analysis are shown in Figure 3C. The meta-regression model, including log opioid dose and enrichment study design, showed there was a significant effect of opioid dose on treatment effect, with a 12.0 point greater pain relief for every 1 log unit increase in dose (P = .046) (ie, 10 mg of morphine equivalents). The model predicts that clinically important effects are not seen within the dose range evaluated (≤240-mg morphine equivalents per day). The effect of enrichment study designwas not statistically significant (P = .69). Together, logmorphine-equivalent dose and enrichment study design accounted for 11% of variance in treatment effect. Results from the multivariate analysis exploring dichotomous dose and enrichment study design showed no statistically significant effect of dose (P = .52) or enrichment study design (P = .40). Treatment Discontinuation and Loss to Follow-up The proportion of participants given an opioid analgesic who were withdrawn from a trial owing to adverse events or lack of efficacy and the proportion lost to follow-up are shown in Figure 4 with more detailed information in eTable 6 in the Supplement. In the 8 trials (10 treatment contrasts) using an enrichment study design, only 20.3% to 48.4% remained in the trial and contributed data to the efficacy estimate, and in the nonenrichment study design this was 39.8% to 75.0%. Irrespective of study design, the predominant causes for dropout were adverse events or lack of efficacy, with half of trials having 50% of participants drop out owing to these 2 reasons. Even in the enrichment trials, where participants entered the trial only if they tolerated and responded to themedicine in the run-in phase, from 31.4% to 61.9% withdrew owing to adverse events and 3.3% to 29.6% withdrew owing to lack of efficacy in the randomized phase of the trial. Eight trials32-34,37,38,40,42,47 provided details on the proportion of participants experiencing at least 1 adverse event in the run-in and/or RCT phase. Overall, the median rates (interquartile range [IQR]) of adverse events in theRCT phasewere 49.1% (44.0%-55.0%) for placebo and 68.9.% (55.0%-85.0%) for treatment groups (risk ratio [RR], 1.3; P < .01). Common adverse events reported by participants in opioid analgesic trials included central nervous system adverse events (headache, somnolence, dizziness), gastrointestinal tract adverse events (constipation, nausea, vomiting), and autonomic adverse events, such as dry mouth. In some studies,33,34,38 over half of participants who experienced an adverse event completed the study. Studies rarely reported the severity or duration of adverse events, therefore it was not possible to categorize adverse events based on severity (see eTables 7 and 8 in the Supplement).
Discussion This review has found that there is evidence that opioid analgesics relieve pain in the short and intermediate term for people with chronic (but not acute) low back pain, but it is uncertain if they improve disability. Treatment effects are small, being half the threshold for clinical importance. The medicines are also commonly associated with adverse events. We found some evidence of a greater effect of opioid analgesics with larger doses; however, the effects are not likely to be clinically important even at high doses. A detailed analysis of dropouts from trials revealed that under half of participants entering these trials contributed to treatment effect size estimates. There is no evidence on long-term use and limited evidence for acute low back pain. The strengths of this review include a consideration of opioid dose and study design as well as a comprehensive search strategy covering single-ingredient and combination opioid analgesics used to treat low back pain. The PEDro scale was used to assess risk of bias because it has acceptably high clinometric properties,18-20 whereas limitations have been reported for the Cochrane risk of bias scale.49,50 Limitations of this review include possible publication bias, as only studies published in peer-reviewedjournalswere included. A limitation of themetaregression is that it does not account for variability in dose response as a result of duration of treatment or intrinsic factors (eg, genetic variability). Our review challenges the prevailing view that opioid medicines are powerful analgesics for low back pain. Opioid analgesics had minimal effects on pain, and even at high doses the magnitude of the effect is less than the accepted thresholds for a clinically important treatment effect on pain.
Conclusions In people with chronic low back pain, opioid analgesics provide short and/or intermediate pain relief, though the effect is small and not clinically important even at higher doses.Many trial patients stopped taking themedicine because they did not tolerate or respond to the medicine. There is no evidence on opioid analgesics for acute low back pain or to guide prolonged use of these medicines in the treatment of people with chronic low back pain.
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