Zomepirac, placebo and paracetamol/dextropropoxyphene combination compared in orthopaedic postoperative pain

Animal models of acute surgical pain

Animal models of tissue injury have been used to investigate the mechanisms of pain. Here, we describe a variety of animal models that have been used to mimic acute surgical pain in human subjects, which include the plantar, tail, and gastrocnemius incision models. We also provide discussion on animal models of laparotomy, thoracotomy, visceral pain, and bone injury. Preclinical studies using these models have provided insights into the mechanisms and causes of acute surgical pain as well as the treatment options to control postsurgical pain.

Analgesics for pain after traumatic or orthopaedic surgery: what is the evidence-a systematic review

OBJECTIVE

To assess analgesic drugs in the treatment of postoperative pain after traumatic and orthopaedic surgery (TOS).

DESIGN

A systematic review of randomised clinical trials (RCTs).

DATA SOURCES

Electronic PubMed, EMBASE, The Cochrane Library, and hand searches.

STUDY SELECTION

RCTs of analgesics administered by oral, intramuscular, intravenous, subcutaneous or rectal route, were compared to other analgesics or placebo, in patients under TOS. Study design, characteristics of the study population, analgesic drugs tested, pain intensity and pain relief scores, and adverse effects were assessed.

RESULTS

Ninety-two RCTs (9,596 patients) met our inclusion criteria. Forty-two (46%) were placebo-controlled, and 50 (54%) were direct comparisons between non-opioid, opioid, and/or combinations of both. Patients' mean age (SD) was 49 years (18). In most trials, gastrointestinal ulcer, liver and renal diseases were exclusion criteria. Only 30 trials (33%) were double-blind and reported standardised outcomes of pain intensity and pain relief; 19 of these were single-dose, and follow up of analgesic effects lasted no more than 12 h in 23 (77%). Globally, only nine trials (10%) were double blind, described dropouts or withdrawals, performed analysis by intention to treat, and reported the effects magnitude.

CONCLUSION

Evidence from RCTs on the treatment of postoperative pain after TOS is inadequate for clinical decision making. Assessment of analgesics in pain after TOS should be based on agreed clinically relevant outcomes, in representative patients, and for longer observation periods. In addition, it should include direct comparisons between candidate drugs or their combinations and between various drug administration schedules.

Dextropropoxyphene: safety and efficacy in older patients

Dextropropoxyphene, alone or in combination with acetaminophen (paracetamol), is among the most frequently prescribed opioid analgesics in the elderly in the US despite the American Geriatric Society recommendation that its use should be restricted. However, this recommendation is based on expert opinion in an apparent absence of data. Accordingly, we conducted a literature search which identified nine studies that reported efficacy and safety data for dextropropoxyphene in predominantly older patients (> or = 55 years of age). These studies were evaluated to assess the efficacy and safety of dextropropoxyphene compared with other opioids and to evaluate whether safety and tolerability differed in older versus younger patients. The efficacy of dextropropoxyphene appeared to be similar to that of other analgesics, and its safety was comparable to that of other opioid analgesics. Although the adverse event profile suggests that elderly patients might have more frequent gastrointestinal and CNS complaints than younger patients treated with dextropropoxyphene, the frequency of reports appears similar to that of other opioids. The incidences of dizziness and somnolence were not significantly greater in older patients (1-2% and 0-21%, respectively) than in younger patients (8% and 13%, respectively). The absence of clinical studies directly addressing the safety and tolerability of dextropropoxyphene in elderly patients (>65 years of age) versus younger patients encumbers assessment of the validity of restricting its use in the elderly. Careful outcomes research is needed to assess the effectiveness and safety of dextropropoxyphene in older patients and to develop evidence-based risk/benefit prescribing criteria for use of this drug in this age group.

A systematic review of trial methodology, using the placebo groups of randomized controlled trials in paediatric postoperative pain

Trial methodology was evaluated in paediatric analgesic studies. Databases were searched for randomised, placebo controlled studies of systemic paracetamol, NSAIDs and opioids administered for acute postoperative pain in children. Eighty-three studies met the inclusion criteria and 40 were included for the analysis. Analgesics were administered for established postoperative pain in two studies only. In all other studies they were administered in a prophylactic manner. As study design and sensitivity are particularly demanding in studies using pre-emptive dosing of analgesics, the placebo groups were analysed for issues of study sensitivity. Postoperative pain outcomes included pain scores in 34, rescue analgesia in 36, time to first rescue analgesia in 15, pain on activity in eight, number of patients with pain in six, pain relief in three, global efficacy rating in two and analgesic consumption via PCA in four studies. Twenty of 36 studies reported criteria for rescue analgesia that varied from 20 to 77% of the maximum pain intensity. Need of rescue analgesia showed more often differences between study groups than time to first rescue analgesia or pain intensity. Rescue analgesia was administered to 21-100% of the patients in the placebo groups where no other analgesics were given perioperatively. Most patients in the placebo groups had pain that was greater than 30% of the maximum. In conclusion, analysis of the methodology showed several aspects of trial design that can be improved in future studies. Placebo control groups can be used in paediatric analgesic studies to demonstrate internal sensitivity.

Single dose dextropropoxyphene, alone and with paracetamol (acetaminophen), for postoperative pain

BACKGROUND

Patient surveys have shown that postoperative pain is often not managed well, and there is a need to assess the efficacy and safety of commonly used analgesics as newer treatments become available. Dextropropoxyphene is one example of an opioid analgesic in current use, and is widely prescribed for pain relief in combination with paracetamol under names such as Co-proxamol and Distalgesic.

OBJECTIVES

To determine the analgesic efficacy and adverse effects of single dose oral Dextropropoxyphene alone and in combination with paracetamol (acetaminophen) for moderate to severe postoperative pain.

SEARCH STRATEGY

Published reports were identified from: Medline (1966 - November 1996), Biological Abstracts (1985 - 1996), Embase (1980 - 1996), the Cochrane Library (Issue 4 1996), and the Oxford Pain Relief Database (1954 - 1994). Additional studies were identified from the reference lists of retrieved reports. Date of the most recent searches: July 1998.

SELECTION CRITERIA

The inclusion criteria used were: full journal publication, postoperative pain, postoperative oral administration, adult patients, baseline pain of moderate to severe intensity, double-blind design, and random allocation to treatment groups which included dextropropoxyphene and placebo or a combination of dextropropoxyphene plus paracetamol and placebo.

DATA COLLECTION AND ANALYSIS

Data were extracted by two independent reviewers, and trials were quality scored. Summed pain intensity and pain relief data were extracted and converted into dichotomous information to yield the number of patients with at least 50% pain relief. This was used to calculate the relative benefit and number-needed-to-treat (NNT) for one patient to achieve at least 50% pain relief.

MAIN RESULTS

Six trials (440 patients) compared dextropropoxyphene with placebo and five (963 patients) compared dextropropoxyphene plus paracetamol 650 mg with placebo. For a single dose of dextropropoxyphene 65 mg in postoperative pain the NNT for at least 50% pain relief was 7.7 (95% confidence interval 4.6 to 22) when compared with placebo over 4-6 hours. For the equivalent dose of dextropropoxyphene combined with paracetamol 650 mg the NNT was 4.4 (3.5 to 5.6) when compared with placebo. These results were compared with those for other analgesics obtained from equivalent systematic reviews. Pooled data showed increased incidence of central nervous system adverse effects for dextropropoxyphene plus paracetamol compared with placebo.

REVIEWER'S CONCLUSIONS

The combination of dextropropoxyphene 65 mg with paracetamol 650 mg shows similar efficacy to tramadol 100 mg for single dose studies in postoperative pain but with a lower incidence of adverse effects. The same dose of paracetamol combined with 60 mg codeine appears more effective but, with the slight overlap in the 95% confidence intervals, this conclusion is not robust. Adverse effects of both combinations were similar. Ibuprofen 400 mg has a lower (better) NNT than both dextropropoxyphene 65 mg plus paracetamol 650 mg and tramadol 100 mg.

Deriving dichotomous outcome measures from continuous data in randomised controlled trials of analgesics

Reports of RCTs of analgesics frequently describe results of studies in the form of mean derived indices, rather than using discontinuous events--such as number or proportion of patients with 50% pain relief. Because mean data inadequately describe information with a non-normal distribution, combining mean data in systematic reviews may compromise the results. Showing that dichotomous data can reliably be derived from mean data, at least in acute pain models, indicates that more meaningful overviews or meta-analysis may be possible. This study investigated the relationship between continuous and dichotomous analgesic measures in a set of individual patient data, and then used that relationship to derive dichotomous from continuous information in randomised controlled trials (RCTs) of analgesics. Individual patient information from 13 RCTs of parallel-group and crossover design in acute postoperative pain was used to calculate the percentage of the maximum possible pain relief score (%maxTOTPAR) and the proportion of patients with greater than 50% pain relief (> 50%maxTOTPAR) for the different treatments. The relationship between the measures was investigated in 45 actual treatments and 10,000 treatments simulated using the underlying actual distribution; 1283 patients had 45 separate treatments. Mean %maxTOTPAR correlated with the proportion of patients with > 50%maxTOTPAR (r2 = 0.90). The relationship calculated from all the 45 treatments predicted to within three patients the number of patients with more than 50% pain relief in 42 of 45 treatments, and 98.8% of 10,000 simulated treatments. For seven effective treatments, actual numbers-needed-to-treat (NNT) to achieve > 50%maxTOTPAR compared with placebo were very similar to those derived from calculated data.

Variation in the placebo effect in randomised controlled trials of analgesics: all is as blind as it seems

The objective was to investigate the relationship between pain relief scores produced by placebo and by active interventions in randomised controlled trials (RCTs). Individual patient categorical pain relief scores from 5 placebo-controlled single-dose parallel-group RCTs in acute postoperative pain were used to calculate the percentage of the maximum possible pain relief score (%maxTOTPAR) for the different treatments. One hundred and thirty of the 525 patients in the 5 trials had a placebo. Individual patients' scores with placebo varied from 0 to 100% of the maximum possible pain relief. The proportion who obtained more than 50% of the maximum possible pain relief with placebo varied from 7% to 37% across the trials; with the active drugs the variation was from 5 to 63%. Mean placebo scores were related to the mean score for the active treatments in each study; the higher the mean active score, the higher the mean placebo score. This relationship disappeared when median values were used. Medical folklore has it that the amount of relief obtained with placebo is one-third of the maximum possible (and does not vary), and that one-third of patients respond to placebo. The results show that the amount of relief obtained with placebo varies considerably between patients, that 38% of patients obtained more than 10% of the maximum possible relief, and 16% obtained greater than 50%. In double-blind, randomised parallel-group studies of high quality placebo scores should not vary. Despite these conditions being met the placebo scores did vary. The previous explanation, of a relationship between the mean placebo scores and the mean scores for the active treatments was not supported.

An evaluation of pre- and postoperative nonsteroidal antiinflammatory drugs in patients undergoing knee arthroscopy. A prospective, randomized, double-blinded study

The potential benefits of a nonsteroidal antiinflammatory drug to 67 patients undergoing knee arthroscopy were evaluated in a prospective, randomized, placebo-controlled, double-blinded study. Group A received the drug (diclofenac, 75 mg twice daily) for 3 to 5 days before and for 7 days after surgery. Group B received a placebo preoperatively and the drug postoperatively. Group C received a placebo at both times. Codeine was available postoperatively for all patients if needed. Outcomes reported by the subjects included pain, crutch use, and return to activities. Outcomes assessed by physicians included knee effusion, range of motion, and gait. Knee flexion and extension strengths were measured isokinetically pre- and postoperatively. Pain scores on the 1st postoperative day were higher in Group C than in Group A. Pain scores at all other time points were not significantly different in the three treatment groups. Groups A and B required less codeine during the first 72 hours after surgery than Group C (mean, 2.9 +/- 1.0 versus 6.8 +/- 1.0 pills). Recovery of function, recovery of strength, and physical examination parameters were not significantly different in the three treatment groups. Diclofenac was an effective analgesic in the immediate postoperative period. Recovery from arthroscopy, however, was not enhanced by taking the drug.

A double blind trial of NSAID versus placebo during rehabilitation

Forty patients participated in a randomized, parallel, double blind study of piroxicam, 20 mg daily, versus placebo, given orally for 10 days following open partial meniscectomy. On day 1, 3, 7, 11, and 21 after surgery the following parameters were studied: quadriceps torque measured isokinetically; patients' assessment of pain; active and passive range of motion measured with goniometer; degree of swelling and irritation of the operated knee; and efficacy of the medication. The mean values for all parameters, except for pain assessment, were in favor of the piroxicam group. This difference was most marked on day 7 and 11 and on these days highly significant. Our findings indicate that piroxicam may be able to improve early postoperative rehabilitation.

Mild analgesics and the accident and emergency department--cost and safety more important than potency?

A prospective controlled trial involving over 1000 patients did not reveal any difference between four drugs commonly used in accident and emergency departments for the relief of mild to moderate pain. There were no significant variations in therapeutic effect, side-effects or patient compliance. When considering the supply of analgesics which may be no more potent than those available without prescription from retail chemists, cost and safety are more important than analgesic effect. By restricting the choice of analgesics available, the accident and emergency department should be able to increase awareness among its staff of the actions and side-effects of a small number of prescribed drugs and to contain costs.