An appraisal of codeine as an analgesic: single-dose analysis

Single dose oral codeine, as a single agent, for acute postoperative pain in adults

BACKGROUND

Codeine is an opioid metabolised to active analgesic compounds, including morphine. It is widely available by prescription, and combination drugs including low doses of codeine are commonly available without prescription.

OBJECTIVES

To assess the efficacy, the time to onset of analgesia, the time to use of rescue medication and any associated adverse events of single dose oral codeine in acute postoperative pain.

SEARCH STRATEGY

We searched CENTRAL, MEDLINE, EMBASE and PubMed to November 2009.

SELECTION CRITERIA

Single oral dose, randomised, double-blind, placebo-controlled trials of codeine for relief of established moderate to severe postoperative pain in adults.

DATA COLLECTION AND ANALYSIS

Studies were assessed for methodological quality and data independently extracted by two review authors. Summed total pain relief (TOTPAR) or pain intensity difference (SPID) over 4 to 6 hours were used to calculate the number of participants achieving at least 50% pain relief, which were used to calculate, with 95% confidence intervals, the relative benefit compared to placebo, and the number needed to treat (NNT) for one participant to experience at least 50% pain relief over 4 to 6 hours. Numbers using rescue medication over specified time periods, and time to use of rescue medication, were sought as additional measures of efficacy. Data on adverse events and withdrawals were collected.

MAIN RESULTS

Thirty-five studies were included (1223 participants received codeine 60 mg, 27 codeine 90 mg, and 1252 placebo). Combining all types of surgery (33 studies, 2411 participants), codeine 60 mg had an NNT of at least 50% pain relief over 4 to 6 hours of 12 (8.4 to 18) compared with placebo. At least 50% pain relief was achieved by 26% on codeine 60 mg and 17% on placebo.Following dental surgery the NNT was 21 (12 to 96) (15 studies, 1146 participants), and following other types of surgery the NNT was 6.8 (4.6 to 13) (18 studies, 1265 participants). The NNT to prevent use of rescue medication within 4 to 6 hours was 11 (6.3 to 50) (11 studies, 765 participants, mostly non-dental); the mean time to its use was 2.7 hours with codeine and 2.0 hours with placebo. More participants experienced adverse events with codeine 60 mg than placebo; the difference was not significant and none were serious. Two adverse event withdrawals occurred with placebo.

AUTHORS' CONCLUSIONS

Single dose codeine 60 mg provides good analgesia to few individuals, and does not compare favourably with commonly used alternatives such as paracetamol, NSAIDs and their combinations with codeine, especially after dental surgery; the large difference between dental and other surgery was unexpected. Higher doses were not evaluated.

Single dose oral paracetamol (acetaminophen) with codeine for postoperative pain in adults

BACKGROUND

This is an updated version of the Cochrane review published in Issue 4, 1998. Combining drugs from different classes with different modes of action may offer opportunity to optimise efficacy and tolerability, using lower doses of each drug to achieve the same degree of pain relief. Previously we concluded that addition of codeine to paracetamol provided additional pain relief, but at expense of additional adverse events. New studies have been published since. This review sought to evaluate efficacy and safety of paracetamol plus codeine using current data, and compare findings with other analgesics evaluated similarly.

OBJECTIVES

Assess efficacy of single dose oral paracetamol plus codeine in acute postoperative pain, increase in efficacy due to the codeine component, and associated adverse events.

SEARCH STRATEGY

We searched CENTRAL, MEDLINE, EMBASE, the Oxford Pain Relief Database in October 2008 for this update.

SELECTION CRITERIA

Randomised, double-blind, placebo-controlled trials of paracetamol plus codeine, compared with placebo or the same dose of paracetamol alone, for relief of acute postoperative pain in adults.

DATA COLLECTION AND ANALYSIS

Two authors assessed trial quality and extracted data. The area under the "pain relief versus time" curve was used to derive proportion of participants with paracetamol plus codeine and placebo or paracetamol alone experiencing least 50% pain relief over four-to-six hours, using validated equations. Number-needed-to-treat-to-benefit (NNT) was calculated using 95% confidence intervals (CIs). Proportion of participants using rescue analgesia over a specified time period, and time to use of rescue analgesia, were sought as additional measures of efficacy. Information on adverse events and withdrawals were collected.

MAIN RESULTS

Twenty-six studies, with 2295 participants, were included comparing paracetamol plus codeine with placebo. Significant dose response was seen for the outcome of at least 50% pain relief over four-to-six hours, with NNTs of 2.2 (95% CI 1.8 to 2.9) for 800 to 1000 mg paracetamol plus 60 mg codeine, 3.9 (2.9 to 4.5) for 600 to 650 mg paracetamol plus 60 mg codeine, and 6.9 (4.8 to 12) for 300 mg paracetamol plus 30 mg codeine. Time to use of rescue medication was over four hours with paracetamol plus codeine and two hours with placebo. The NNT to prevent remedication was 5.6 (4.0 to 9.0) for 600 mg paracetamol plus 60 mg codeine over four to six hours. Adverse events increased of mainly mild to moderate severity with paracetamol plus codeine than placebo.Fourteen studies, with 926 participants, were included in the comparison of paracetamol plus codeine with the same dose of paracetamol alone. Addition of codeine increased proportion of participants achieving at least 50% pain relief over four-to-six hours by 10 to 15%, increased time to use of rescue medication by about one hour, and reduced proportion of participants needing rescue medication by about 15% (NNT to prevent remedication 6.9 (4.2 to 19). Adverse events were mainly mild to moderate in severity and incidence did not differ between groups.

AUTHORS' CONCLUSIONS

This update confirms previous findings that combining paracetamol with codeine provided clinically useful levels of pain relief in about 50% of patients with moderate to severe postoperative pain, compared with under 20% with placebo. New information for remedication shows that the combination extended the duration of analgesia by about one hour compared to treatment with the same dose of paracetamol alone. At higher doses, more participants experienced adequate pain relief, but the amount of information available for the 1000 mg paracetamol plus 60 mg codeine dose was small, and based on limited information.

Single dose oral paracetamol (acetaminophen) for postoperative pain in adults

BACKGROUND

This is an updated version of the original Cochrane review published in Issue 1, 2004 - this original review had been split from a previous title on 'Single dose paracetamol (acetaminophen) with and without codeine for postoperative pain'. The last version of this review concluded that paracetamol is an effective analgesic for postoperative pain, but additional trials have since been published. This review sought to evaluate the efficacy and safety of paracetamol using current data, and to compare the findings with other analgesics evaluated in the same way.

OBJECTIVES

To assess the efficacy of single dose oral paracetamol for the treatment of acute postoperative pain.

SEARCH STRATEGY

We searched The Cochrane Library, MEDLINE, EMBASE, the Oxford Pain Relief Database and reference lists of articles to update an existing version of the review in July 2008.

SELECTION CRITERIA

Randomised, double-blind, placebo-controlled clinical trials of paracetamol for acute postoperative pain in adults.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and extracted data. Area under the "pain relief versus time" curve was used to derive the proportion of participants with paracetamol or placebo experiencing at least 50% pain relief over four to six hours, using validated equations. Number-needed-to-treat-to-benefit (NNT) was calculated, with 95% confidence intervals (CI). The proportion of participants using rescue analgesia over a specified time period, and time to use, were sought as measures of duration of analgesia. Information on adverse events and withdrawals was also collected.

MAIN RESULTS

Fifty-one studies, with 5762 participants, were included: 3277 participants were treated with a single oral dose of paracetamol and 2425 with placebo. About half of participants treated with paracetamol at standard doses achieved at least 50% pain relief over four to six hours, compared with about 20% treated with placebo. NNTs for at least 50% pain relief over four to six hours following a single dose of paracetamol were as follows: 500 mg NNT 3.5 (2.7 to 4.8); 600 to 650 mg NNT 4.6 (3.9 to 5.5); 975 to 1000 mg NNT 3.6 (3.4 to 4.0). There was no dose response. Sensitivity analysis showed no significant effect of trial size or quality on this outcome.About half of participants needed additional analgesia over four to six hours, compared with about 70% with placebo. Five people would need to be treated with 1000 mg paracetamol, the most commonly used dose, to prevent one needing rescue medication over four to six hours, who would have needed it with placebo. Adverse event reporting was inconsistent and often incomplete. Reported adverse events were mainly mild and transient, and occurred at similar rates with 1000 mg paracetamol and placebo. No serious adverse events were reported. Withdrawals due to adverse events were uncommon and occurred in both paracetamol and placebo treatment arms.

AUTHORS' CONCLUSIONS

A single dose of paracetamol provides effective analgesia for about half of patients with acute postoperative pain, for a period of about four hours, and is associated with few, mainly mild, adverse events.

Liver enzyme induction and inhibition: implications for anaesthesia

Recent breakthroughs in molecular biology have enabled a reclassification of drug metabolising enzymes based on their amino acid sequence. This has led to a better understanding of drug metabolism and drug interactions. The majority of these drug metabolising enzymes may be either induced or inhibited by drugs or by extraneous substances including foodstuffs, cigarette smoke and environmental pollutants. Virtually all drugs used in anaesthesia are metabolised by either hepatic phase 1 or phase II enzymes. This review considers the classification of drug metabolising enzymes, explains the mechanisms of enzyme induction and inhibition, and also considers how the action of drugs commonly used by anaesthetists, including opioids and neuromuscular blocking drugs, may be altered by this mechanism.

Single dose oral paracetamol (acetaminophen) for postoperative pain

BACKGROUND

Paracetamol (acetaminophen) and non-steroidal anti-inflammatory drugs (NSAIDs) are widely used for the relief of mild and moderate pain arising from headache, musculoskeletal conditions and dysmenorrhoea. A prior Cochrane systematic review concluded that paracetamol is also effective for postoperative pain, but additional trials have since been published. This review sought to evaluate the efficacy and safety of paracetamol using current data, and to compare the findings with other analgesics evaluated in the same way.

OBJECTIVES

To assess the efficacy of single dose oral paracetamol for the treatment of acute postoperative pain.

SEARCH STRATEGY

We searched the Cochrane Library (Issue 3, 2002), the trials register of the Cochrane Pain, Palliative and Supportive Care group (November 2002); MEDLINE (1966 to May 1996); PubMed (1996 to August 2001); EMBASE (1980 to 1996); the Oxford Pain Relief Database (1950 to 1994); and reference lists of articles in order to update an existing version of the review.

SELECTION CRITERIA

Randomised, double-blind, placebo-controlled clinical trials of paracetamol for acute postoperative pain in adults.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed trial quality and extracted data. The area under the 'pain relief versus time' curve was used to derive the proportion of patients with paracetamol or placebo experiencing least 50% pain relief over four to six hours using validated equations. The number-needed-to-treat (NNT) was calculated using 95% confidence intervals. Information on adverse effects was also collected.

MAIN RESULTS

Forty-seven reports that enrolled 4186 patients (2561 patients were treated with a single oral dose of paracetamol and 1625 with placebo) met the inclusion criteria and were included in the analyses. The NNTs for at least 50% pain relief over four to six hours following a single dose of paracetamol were as follows: 325 mg NNT 3.8 (2.2 to 13.3); 500 mg NNT 3.5 (2.7 to 4.8); 600/650 mg NNT 4.6 (3.9 to 5.5); 975/1000 mg NNT 3.8 (3.4 to 4.4); and 1500 mg NNT 3.7 (2.3 to 9.5). Sub-group analysis showed no significant differences between smaller and larger trials, or lower and higher quality trials. Drug-related study withdrawals were rarely reported. Studies reported a variable incidence of adverse effects that were generally mild and transient. There were no statistically significant differences in the frequency of reported adverse effects between paracetamol 975/1000 mg and placebo.

REVIEWER'S CONCLUSIONS

Single doses of paracetamol are effective analgesics for acute postoperative pain and give rise to few adverse effects.

Pharmacogenetics of codeine metabolism in an urban population of children and its implications for analgesic reliability

BACKGROUND

Codeine analgesia is wholly or mostly due to its metabolism to morphine by the cytochrome P450 enzyme CYP2D6, which shows significant genetic variation in activity. The aims of this study were to investigate genotype, phenotype and morphine production from codeine in children undergoing adenotonsillectomy, and to compare analgesia from codeine or morphine combined with diclofenac.

METHODS

Ninety-six children received either codeine 1.5 mg kg(-1) or morphine 0.15 mg kg(-1) in a randomized, double-blind design. Genetic analysis was performed and plasma morphine concentrations at 1 h were determined. Postoperative analgesia and side-effects were recorded.

RESULTS

Forty-seven per cent of children had genotypes associated with reduced enzyme activity. Mean (SD) morphine concentrations were significantly lower (P<0.001) after codeine [4.5 (0.3) ng ml(-1)] than after morphine [24.7 (1.5) ng ml(-1)], and morphine and its metabolites were not detected in 36% of children given codeine. There was a significant relationship between phenotype and plasma morphine (P=0.02). More children required rescue analgesia after codeine at both 2 (P<0.05) and 4 h after administration (P<0.01). Fifty-six per cent of children vomited after morphine and 29% after codeine (P<0.01). Neither phenotype nor morphine concentration was correlated with either pain score or the need for rescue analgesia (r=-0.21, 95% confidence interval -0.4, -0.01).

CONCLUSIONS

Reduced ability for codeine metabolism may be more common than previously reported. Plasma morphine concentration 1 h after codeine is very low, and related to phenotype. Codeine analgesia is less reliable than morphine, but was not well correlated with either phenotype or plasma morphine in this study.

Paracetamol versus paracetamol-codeine in the treatment of post-operative dental pain: a randomized, double-blind, prospective trial

BACKGROUND

Codeine is frequently added to paracetamol to treat post-operative dento-alveolar pain; studies have shown effectiveness in relief of post-operative pain at high doses but at the expense of central nervous and gastrointestinal side effects. There has been no trial to compare the efficacy and safety of paracetamol 1000 mg with paracetamol 1000 mg combined with codeine 30 mg.

METHOD

A randomized, single centre, double-blind prospective parallel group trial was performed to compare paracetamol 1000 mg with paracetamol 1000 mg with codeine 30 mg for the relief of pain following surgical removal of impacted third molars, and analysed on an intention-to-treat (ITT) basis. Eighty-two patients were assigned randomly to receive either drug for a maximum of three doses. Patients recorded their pain intensity one hour after surgery and hourly thereafter for 12 hours.

RESULTS

The average increase in pain intensity over 12 hours was significantly less in patients receiving paracetamol plus codeine than in those receiving paracetamol alone (p=0.03) -1.81 cm/h compared with 0.45 cm/h - a difference of 1.13 cm/h (95 per cent CI: 0.18 to 2.08). Of the patients who received the paracetamol codeine combination, 62 per cent used escape medication compared with 75 per cent of those on paracetamol alone (p=0.20). There was no significant difference between the two groups in the proportion of patients experiencing adverse events (p=0.5).

CONCLUSION

A combination of 1000 mg paracetamol and 30 mg codeine was significantly more effective in controlling pain for 12 hours following third molar removal, with no significant difference of side effects during the 12 hour period studied.

The pharmacogenetics of analgesia: toward a genetically-based approach to pain management

Interindividual differences in the experience of pain have been appreciated clinically for over a century. More recently, there has been a growing body of evidence demonstrating differences in analgesic response to various pharmacotherapies, although the source of this variability largely remains to be explained. To this end, basic science research is beginning to identify the allelic variants that underlie such antinociceptive variability using a multiplicity of animal models, and powerful genetic approaches are being exploited to accelerate this process. Although the vast majority of these studies have focused on the pharmacogenetics of opioids, owing to their prominent status as analgesics, the number of pharmacotherapies evincing genetically-based variability is rapidly expanding. In addition, analogous studies have been undertaken in humans, as a small but growing number of clinical trials have begun to evaluate prospectively the existence, if oftentimes not the origin, of interindividual differences in analgesic drug response. Importantly, with a few notable exceptions, such efforts have primarily identified differences in analgesic efficacy and/or potency between male and female human subjects. Looking toward the future development of one or more widely utilised, pharmacogenetic screens that would lead to modifications in treatment planning, at least with respect to the pharmacologic management of pain, this review will document the breadth of genetically-based variability in drug-mediated antinociception in animals. Specific examples in which the gene or genes underlying such variability have been postulated or identified will be given, while highlighting the effect of sex and its interactions with other genetic backgrounds. Finally, we will summarise and evaluate the literature on pharmacogenetic differences in human analgesic drug response, for which the influence of sex has served as one of the better studied and heuristically insightful examples.

Using evidence from different sources: an example using paracetamol 1000 mg plus codeine 60 mg

BACKGROUND

Meta-analysis usually restricts the information pooled, for instance using only randomised, double-blind, placebo-controlled trials. This neglects other types of high quality information. This review explores using different information for the combination of paracetamol 1000 mg and codeine 60 mg in acute postoperative pain.

RESULTS

Randomised, double-blind, placebo-controlled trials of paracetamol 1000 mg and codeine 60 mg had an NNT of 2.2 (95% confidence interval 1.7 to 2.9) for at least 50% pain relief over four to six hours in three trials with 197 patients. Computer simulation of randomised trials demonstrated 92% confidence that the simulated NNT was within +/- 0.5 of the underlying value of 2.2 with this number of patients. The result was supported a rational dose-response relationship for different doses of paracetamol and codeine in 17 additional trials with 1,195 patients. Three controlled trials lacking a placebo and with 117 patients treated with of paracetamol 1000 mg and codeine 60 mg had 73% (95%CI 56% to 81%) of patients with at least 50% pain relief, compared with 57% (48% to 66%) in placebo controlled trials. Six trials in acute pain were omitted because of design issues, like the use of different pain measures or multiple dosing regimens. In each paracetamol 1000 mg and codeine 60 mg was shown to be better than placebo or comparators for at least one measure.

CONCLUSIONS

Different designs of high quality trials can be used to support limited information used in meta-analysis without recourse to low quality trials that might be biased.

Variable cytochrome P450 2D6 expression and metabolism of codeine and other opioid prodrugs: implications for the Australian anaesthetist

Codeine is a popular opioid prodrug dependent on the activity of the specific cytochrome P450 enzyme 2D6 (CYP2D6). This enzyme catalyses the production of the potent analgesic metabolite morphine, but genetic studies have demonstrated that individuals from different ethnic groups exhibit considerable variability in the functional capacities of their expressed CYP2D6 enzymes, and pharmacological studies have shown many commonly prescribed drugs can reduce the action of CYP2D6 enzymes. These findings have significant clinical implications for the rational prescription of effective analgesia, especially in a multicultural country like Australia.

Single dose paracetamol (acetaminophen), with and without codeine, 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. Paracetamol (acetaminophen) is an important non-opiate analgesic, commonly prescribed, as well as being available for retail sale. This review seeks to examine the efficacy of paracetamol alone and in combination with codeine, and also considers adverse effects.

OBJECTIVES

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

SEARCH STRATEGY

Published trials were identified from: Medline (1966 to May 1996), Embase (1980 to 1996), Cochrane Library (Issue 2 1996) and the Oxford Pain Relief Database (1950 to 1994). Additional trials were identified from reference lists of retrieved studies. Date of most recent searches: July 1998.

SELECTION CRITERIA

Inclusion criteria 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 compared paracetamol with placebo or a combination of paracetamol and codeine with either placebo or the same dose of paracetamol alone.

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 over 4 to 6 hours compared with placebo. Adverse effects were used to calculate relative risk and number-needed-to-harm (NNH).

MAIN RESULTS

We found 40 trials of paracetamol against placebo (4171 patients), 22 trials of paracetamol plus codeine against placebo (1407 patients) and 12 trials of paracetamol plus codeine against the same dose of paracetamol (794 patients). In postoperative pain paracetamol 1000 mg had an NNT of 4.6 (3.8-5.4) for at least 50% pain relief when compared with placebo, and paracetamol 600/650 mg had an NNT of 5.3 (4.1-7.2). Paracetamol 600/650 mg plus codeine 60 mg had an NNT of 3. 6 (2.9-4.5). Comparing paracetamol plus codeine 60 mg with the same dose of paracetamol alone gave an NNT of 7.7 (5.1-17) for at least 50% pain relief. Adverse effects: Relative risk estimates for paracetamol 600/650 mg plus codeine 60 mg versus placebo showed a significant difference for 'drowsiness'/somnolence (NNH 11 (7.5- 0)) and dizziness (NNH 27 (15-164)) but no significant difference for nausea/vomiting.

REVIEWER'S CONCLUSIONS

Paracetamol is an effective analgesic with a low incidence of adverse effects. The addition of codeine 60 mg to paracetamol produces additional pain relief even in single oral doses, but may be accompanied by an increase in drowsiness and dizziness.

A double-blind comparison of codeine and morphine for postoperative analgesia following intracranial surgery

Codeine and morphine were compared in a double-blind study of postoperative analgesia in 40 patients after intracranial neurosurgery. Eighteen patients received codeine phosphate 60 mg and 18 morphine sulphate 10 mg, both by intramuscular injection; 4 patients (10%) required no analgesia. Both drugs provided analgesia within 20 min of injection but morphine was more effective than codeine beyond 60 min (p = 0.01). Fewer doses of morphine than codeine were required (p = 0.003). Nine patients requested one dose of morphine and 9 two doses. Seven patients required three doses of codeine and 1 patient required four doses. Neither drug caused respiratory depression, sedation, pupillary constriction or unwanted cardiovascular effects. We conclude that, in the doses used, morphine is a safe alternative to codeine for analgesia after neurosurgery and has a more persistent action.

Analgesic efficacy and safety of paracetamol-codeine combinations versus paracetamol alone: a systematic review

OBJECTIVES

To assess whether adding codeine to paracetamol has an additive analgesic effect; to assess the safety of paracetamol-codeine combinations versus paracetamol alone.

DESIGN

Systematic literature review with meta-analysis, methodological quality of published trials being scored by means of 13 predefined criteria.

TRIALS

24 of 29 trials that met the inclusion criteria. Models studied in the trials were postsurgical pain (21), postpartum pain (one), osteoarthritic pain (one), and experimentally induced pain (one).

INTERVENTIONS

Dosages ranged from 400 to 1000 mg paracetamol and 10 to 60 mg codeine.

MAIN OUTCOME MEASURES

The sum pain intensity difference (efficacy analysis) and the proportion of patients reporting a side effect (safety analysis).

RESULTS

Most trials were considered of good to very good quality. Only the single dose studies could be combined for analysis of analgesic efficacy. Pooled efficacy results indicated that codeine added to paracetamol provided a 5% increase in analgesia on the sum pain intensity difference. This effect was comparable to the difference in analgesic effect between codeine and placebo. The cumulative incidence of side effects with each treatment was comparable in the single dose trials. In the multidose studies a significantly higher proportion of side effects occurred with paracetamol-codeine preparations.

CONCLUSION

The difference is analgesic effect between paracetamol-codeine combinations and paracetamol alone was small but statistically significant. In the multidose studies the proportion of patients reporting a side effect was significantly higher with paracetamol-codeine combinations. For occasional pain relief a paracetamol-codeine combination might be appropriate but repeated use increases the occurrence of side effects.

Analgesic efficacy of paracetamol and its combination with codeine and caffeine in surgical pain--a meta-analysis

The objective of this study was to quantify the analgesic efficacy of paracetamol and its combination with codeine or caffeine through a systematic overview and meta-analysis of relevant randomized controlled trials (RCTs). Systematic retrieval of relevant clinical trials was carried out using computerized searches, historical searches and communication with manufacturers. The results of RCTs were pooled to estimate (i) the difference in percentage improvement of total pain relief (TOTPAR%) and the sum of pain intensity difference (SPID%); (ii) the proportions of patients obtaining moderate to excellent pain relief relative to placebo (ResRR) and (iii) the ratio of patients requiring analgesic re-medication (RemRR). Head-to-head comparisons were also undertaken for paracetamol versus its combination with codeine or caffeine. A total of 80 RCT reports describing 103 placebo comparisons and 26 head-to-head comparisons were identified. The total pain relief score in the single dose studies increased by 38 percentage points for paracetamol and by 24 points for placebo. The difference (d) in TOTPAR% between the two was highly significant (d = 14, 95% CI: 12, 16). For the difference in SPID%, d = 12, 95% CI: 11, 13. Patients were more than twice as likely to obtain moderate to excellent pain relief on paracetamol than on placebo (ResRR = 2.39, 95% CI: 1.89, 3.02), and less likely to require re-medication (RemRR = 0.78, 95% CI: 0.69, 0.88). There was no significant (P > 0.05) dose-response relationship. The analgesic efficacy of paracetamol 600 mg was enhanced with the addition of codeine 60 mg (using TOTPAR% as outcome) in both indirect and head-to-head comparisons. SPID%, but not ResRR and RemRR, data supported this conclusion. Much weaker effects were observed with the caffeine combination. Adverse effects were mild. Surprisingly, drowsiness was seen more often with paracetamol and paracetamol-codeine combinations than with placebo. The relative risks (95% CI) were 1.83 (1.29, 2.59) and 2.39 (1.58, 3.57), respectively. In conclusion paracetamol is an effective analgesic for post-surgical pain. Caffeine adds little to the analgesic effect of paracetamol. However, there is some evidence that codeine 60 mg adds to the analgesic effects of paracetamol 600 mg, using pain relief or pain intensity scores as outcomes, but this is not necessarily translated into an increase in number of patients who obtain moderate to excellent pain relief.

Randomized evaluation of controlled-release codeine and placebo in chronic cancer pain

Codeine is widely used in combination with acetaminophen and aspirin for the management of mild to moderate pain. However, there are few controlled clinical trials of single-entity codeine in chronic cancer pain. The purpose of this study was to evaluate the clinical efficacy and safety of controlled-release codeine given every 12 hr in patients with cancer pain. Thirty-five patients with chronic cancer pain were randomized in a double-blind crossover study to controlled-release (CR) codeine or placebo, for 7 days each. Pain intensity was assessed at 0800 hr and 2000 hr using a visual analogue scale (VAS) and a five-point categorical scale, and the use of "rescue" acetaminophen-plus-codeine (300 mg/30 mg every 4 hr as needed) was recorded. Thirty patients completed the study (17 male, 13 female; mean age, 64.4 +/- 9.8 years) with a mean daily CR codeine dose of 277 +/- 77 mg (range, 200-400 mg). CR codeine treatment resulted in significantly lower overall VAS pain intensity scores (22 +/- 18 mm versus 36 +/- 20 mm, P = 0.0001), categorical pain intensity scores (1.2 +/- 0.8 versus 1.8 +/- 0.8, P = 0.0001), and pain scores when assessed by day of treatment and by time of day. Daily "rescue" analgesic consumption was significantly lower on CR codeine, compared to placebo treatment (2.2 +/- 2.3 versus 4.6 +/- 2.8 tablets per day, P = 0.0001). Both patients and investigators preferred CR codeine to placebo (80% versus 3%, P = 0.0014 and 73% versus 7%, P = 0.0160, respectively). These data indicate that CR codeine, given every 12 hr results in significant reductions in pain intensity and the use of "rescue" acetaminophen-plus-codeine in patients with cancer pain. CR codeine provides the benefits of a flexible single entity codeine formulation and the convenience of 12-hr duration of action, which allows patients uninterrupted sleep and improved compliance.

The dose-response relationship of controlled-release codeine (Codeine Contin) in chronic cancer pain

The improved pain control provided by regular dosing of opioid analgesics in patients with severe cancer pain has been well established. However, the treatment of mild-to-moderate cancer pain is often limited to "as needed" dosing with fixed combinations of codeine or oxycodone plus a nonopioid analgesic, which do not allow optimal titration of the individual components. This randomized double-blind study was designed to evaluate the efficacy of controlled-release codeine (Codeine Contin) in patients with cancer pain, and to estimate its dose equivalence to a standard combination of acetaminophen plus codeine. Twenty-four patients with at least moderate cancer pain were randomized to Codeine Contin 100, 200, or 300 mg every 12 hr or acetaminophen plus codeine (600 mg/60 mg) every 6 hr. On days 1 and 4 of dosing, pain intensity and pain relief were assessed hourly for 12 hr. The sum of pain intensity differences (SPID) from baseline and the total pain relief (TOTPAR) scores demonstrated a dose-response relationship for Codeine Contin on days 1 and 4 that was statistically significant on day 1 and suggested greater analgesic efficacy on day 4, compared with day 1. Codeine Contin 150 mg every 12 hr was estimated to be equianalgesic to acetaminophen plus codeine (600 mg/60 mg) given every 6 hr. Because a similar equivalence was also demonstrated from analysis of adverse event data, it is concluded that Codeine Contin 150 mg produces analgesia and a side-effect profile similar to a 40% lower dose of codeine provided by the combination.(ABSTRACT TRUNCATED AT 250 WORDS)

Impact of environmental and genetic factors on codeine analgesia

The polymorphic cytochrome P-450 DB1 (P-450 IID6) is responsible for the O-demethylation of codeine to morphine by human liver microsomes. The influence of P-450 DB1 variable activity on the bioactivation of codeine in vivo to morphine and on its analgesic effect was investigated in phenotyped healthy volunteers--7 extensive [EM] and 1 poor [PM] metabolizer of debrisoquine. After pretreatment with oral placebo or quinidine sulphate 50 mg, codeine phosphate 100 mg or placebo were administered orally according to a double-blind randomized crossover design. In EM subjects the plasma morphine Cmax was 17.9 nmol/l, whereas virtually no morphine was detectable after quinidine pretreatment (1.5 nmol/l), and in the PM subject (0.60 nmol/l). In EM codeine significantly increased subjective (VAS) and objective (R-III reflex) pain thresholds in response to selective transcutaneous nerve stimulation, whereas no significant analgesia was detected after placebo, or after codeine with quinidine pretreatment, or in the PM. In PM of genetic origin, or due to environmental alteration of the phenotypic expression (i.e. drug interaction), codeine is not activated into morphine and is an inefficient analgesic.

Double-blind, placebo controlled comparison of paracetamol and paracetamol plus codeine--a quantitative evaluation by laser induced pain

The aim of the present double-blind, placebo controlled, three-way cross over study was to evaluate the analgesic efficacy of single oral doses of paracetamol 1.0 g and paracetamol 1.0 g plus codeine 60 mg. Pain threshold and brain evoked potentials to laser stimulation were determined hourly for 6 h in 12 healthy volunteers. Pain threshold was significantly elevated compared to placebo 1 and 2 h after paracetamol ingestion. Paracetamol 1.0 g plus codeine 60 mg was superior to placebo 1 to 6 h after medication. Only at 1 and 2 h after ingestion the combined drug was better than paracetamol. The evoked potentials were significantly depressed compared to placebo 2 and 4 h after paracetamol. The combination of paracetamol and codeine was superior to placebo 1 to 6 h after ingestion. The potentials showed no difference between the two active drugs. The total analgesic effect (approximation of area under the time-efficacy curve), showed that the combined drug was superior to plain paracetamol. A higher incidence of adverse effects in 10 of the 12 subjects was observed after ingestion of the combined drug compared to plain paracetamol (1 of 12). Paracetamol appears to exert part of its action by a central effect. There was at least 1 h between the peak plasma concentration of paracetamol and the peak hypoalgesia.

Codeine plus paracetamol versus paracetamol in longer-term treatment of chronic pain due to osteoarthritis of the hip. A randomised, double-blind, multi-centre study

This randomized, double-blind, multi-centre study was undertaken to evaluate the efficacy and safety of treatment for 4 weeks with codeine plus paracetamol versus paracetamol in relieving chronic pain due to osteoarthritis of the hip. A total of 158 outclinic patients entered the study. Eighty-three patients (mean age 66 years) were treated with codeine 60 mg plus paracetamol 1 g 3 times daily, and 75 patients (mean age 67 years) with paracetamol 1 g 3 times daily. Ibuprofen 400 mg was prescribed as rescue medication. Due to an unexpected high rate of adverse drug reactions, the study was closed before the planned 400 patients had entered. Over weeks 1-4, 87%, 64%, 61% and 52% of patients in the codeine plus paracetamol group, and 38%, 31%, 22% and 29% of patients in the paracetamol group had one or more adverse drug reactions. Significantly more patients in the codeine plus paracetamol group had adverse drug reactions in each of the 4 weeks. Nausea, dizziness, vomiting and constipation were predominant adverse reactions in the codeine plus paracetamol group. During the first week of treatment, 30 patients (36%) in the codeine plus paracetamol group and 9 (12%) in the paracetamol group dropped out. As evaluated from patients completing the first week of treatment, the pain intensity during that week compared to their baseline pain was significantly lower in the codeine plus paracetamol group than in the paracetamol group. Moreover, during the first week the paracetamol group received rescue medicine significantly more frequently. In conclusion, when evaluated after 7 days of treatment, the daily addition of codeine 180 mg to paracetamol 3 g significantly reduced the intensity of chronic pain due to osteoarthritis of the hip joint. However, several adverse drug reactions, mainly of the gastrointestinal tract, and the larger number of patients withdrawing from treatment means that the addition of such doses of codeine cannot be recommended for longer-term treatment of chronic pain in elderly patients.

Analysis of the analgesic efficacy of acetaminophen 1000 mg, codeine phosphate 60 mg, and the combination of acetaminophen 1000 mg and codeine phosphate 60 mg in the relief of postoperative pain

Patients who experienced pain after surgery were administered a single dose of 1 of 3 treatments: acetaminophen 1000 mg, codeine phosphate 60 mg, or a combination of these. Patients rated their pain intensity on ordinal and visual analog scales just prior to medication and at intervals thereafter for up to 5 hours. They also rated pain relief, pain half gone, and any adverse effects. Sum of pain intensity difference and total pain relief scores were analyzed using Dunnett's procedure. The drug combination was statistically superior to codeine as measured by SPID, TOTPAR, pain half gone, and time to remedication. The combination achieved better mean scores than acetaminophen on all efficacy measures, but was (marginally) statistically superior only in pain half gone. No appreciable differences in adverse effects were noted among the treatments. The difficulty of showing the analgesic efficacy of codeine in a single dose trial is discussed.

Double-blind parallel comparison of single oral doses of ketoprofen, codeine, and placebo in patients with moderate to severe dental pain

Ketoprofen, 25, 50, and 100 mg, was compared with 90 mg codeine and placebo for relief of pain due to removal of impacted third molar teeth. Treatment was self-administered as a single oral dose under double-blind conditions in five parallel groups established by a random code in healthy young adults. Based on 129 patient evaluations of pain experience and pain relief, ketoprofen was shown to have a more rapid onset and longer duration of action than codeine. In the derived variables of SPID (Sum of Pain Intensity Differences) and TOPAR (Total Pain Relief), all three doses of ketoprofen, with no dose-related differences among them, were found to provide statistically superior analgesia to codeine and placebo. All five treatments were associated with some adverse reactions.

Combination analgesics

Six rationales for using combination analgesics are identified, but most combinations are formulated with two rationales in mind: enhancement of analgesia and reduction of adverse effects by combining two analgesics with different mechanisms of action. Acetaminophen and aspirin are the mainstays of oral analgesic combinations. There is substantial evidence that combining an optimal dose of acetaminophen or aspirin with an oral opioid such as codeine, hydrocodone, or oxycodone produces an additive analgesic effect greater than that obtained by doubling the dose of either constituent administered alone. There is also some evidence that the adverse effects produced by such combinations are less than would be produced by an equi-analgesic dose of a single constituent. The physician need not be confined to existing fixed-ratio combinations; he or she may extemporize to the patient's advantage by co-administering acetaminophen, aspirin, or other nonsteroidal anti-inflammatory drugs with available oral opioids and, in select situations, co-administering oral or injectable analgesics with psychoactive drugs.