Pain thresholds, supra-threshold pain and lidocaine sensitivity in patients with erythromelalgia, including the I848Tmutation in NaV 1.7.

OBJECTIVES: Nociceptive thresholds and supra-threshold pain ratings as well as their reduction upon local injection with lidocaine were compared between healthy subjects and patients with erythromelalgia (EM). METHODS: Lidocaine (0.25, 0.50, 1.0 or 10 mg/mL) or placebo (saline) was injected intradermally in non-painful areas of the lower arm, in a randomized, double-blind manner, to test the effect on dynamic and static mechanical sensitivity, mechanical pain sensitivity, thermal thresholds and supra-threshold heat pain sensitivity. RESULTS: Heat pain thresholds and pain ratings to supra-threshold heat stimulation did not differ between EM-patients (n = 27) and controls (n = 25), neither did the dose-response curves for lidocaine. Only the subgroup of EM-patients with mutations in sodium channel subunits NaV 1.7, 1.8 or 1.9 (n = 8) had increased lidocaine sensitivity for supra-threshold heat stimuli, contrasting lower sensitivity to strong mechanical stimuli. This pattern was particularly clear in the two patients carrying the NaV 1.7 I848T mutations in whom lidocaine's hyperalgesic effect on mechanical pain sensitivity contrasted more effective heat analgesia. CONCLUSION: Heat pain thresholds are not sensitized in EM patients, even in those with gain-of-function mutations in NaV 1.7. Differential lidocaine sensitivity was overt only for noxious stimuli in the supra-threshold range suggesting that sensitized supra-threshold encoding is important for the clinical pain phenotype in EM in addition to lower activation threshold. Intracutaneous lidocaine dose-dependently blocked nociceptive sensations, but we did not identify EM patients with particular high lidocaine sensitivity that could have provided valuable therapeutic guidance. SIGNIFICANCE: Acute pain thresholds and supra-threshold heat pain in controls and patients with erythromelalgia do not differ and have the same lidocaine sensitivity. Acute heat pain thresholds even in EM patients with the NaV 1.7 I848T mutation are normal and only nociceptor sensitivity to intradermal lidocaine is changed. Only in EM patients with mutations in NaV 1.7, 1.8 or 1.9 supra-threshold heat and mechanical pain shows differential lidocaine sensitivity as compared to controls.

The analgesic effect of intravenous ketamine and lidocaine on pain after spinal cord injury.

BACKGROUND: Pain following spinal cord injury (SCI) is a therapeutic challenge. Only a few treatments have been assessed in randomized, controlled trials. The primary objective of the present study was to examine the analgesic effect of ketamine and lidocaine in a group of patients with neuropathic pain below the level of spinal cord injury. We also wanted to assess sensory abnormalities to see if this could help us to identify responders and if treatments resulted in changes of sensibility. METHODS: Ten patients with spinal cord injury and neuropathic pain below the level of injury were included. The analgesic effect of ketamine 0.4 mg kg(-1) and lidocaine 2.5 mg kg(-1) was investigated. Saline was used as placebo. The drugs were infused over 40 min. A randomized, double-blind, three-period, three-treatment, cross-over design was used. Systemic plasma concentrations of ketamine and lidocaine were assessed. Pain rating was performed using a visual analogue scale (VAS). Sensory function was assessed with a combination of traditional sensory tests and quantitative measurement of temperature thresholds. RESULTS: Response to treatment, defined as 50% reduction in VAS-score during infusion, was recorded in 5/10 in the ketamine, 1/10 in the lidocaine and 0/10 in the placebo groups. Neither ketamine nor lidocaine changed temperature thresholds or assessments of mechanical; dynamic and static sensibility. Nor could these sensory assessments predict response to treatment in this setting. Lidocaine and particularly ketamine were associated with frequent side-effects. CONCLUSION: Ketamine but not lidocaine showed a significant analgesic effect in patients with neuropathic pain after spinal cord injury. The pain relief was not associated with altered temperature thresholds or other changes of sensory function.

The effectiveness of intravenous ketamine and lidocaine on peripheral neuropathic pain.

BACKGROUND: Neuropathic pain is often severe and resistant to pharmacological treatment. The aims of the present study were to assess the analgesic effect of ketamine and lidocaine and to investigate if measurement of different variables of sensibility could be used to identify responders. We also wanted to study if treatment resulted in changes of sensibility. METHODS: Twelve patients with long-lasting peripheral neuropathic pain of traumatic origin were included. The effects of ketamine hydrochloride (Ketalar, Parke Davis) 0.4 mg/kg and lidocaine hydrochloride (Xylocain, Astra) 2.5 mg/kg were investigated. Saline was used as placebo. The intensity of continuous pain was measured by a visual analogue scale (VAS). Warm and cold perception as well as heat and cold pain thresholds were assessed. Sensibility to touch was also tested. Systemic plasma concentrations of lidocaine and ketamine were assessed. RESULTS: The mean reduction in VAS-scores was 55%, 34% and 22% for ketamine, lidocaine and placebo, respectively. A significant difference was registered between ketamine and placebo (P = 0.009). Response to treatment (50% reduction in VAS-score during infusion) was recorded in 7/12 in the ketamine, 4/12 in the lidocaine and 2/12 in the placebo group. Quantitative sensory testing (QST) of thermal sensitivity and sensory tests for mechanical stimuli could not separate responders from non-responders and neither were the results from these assessments changed by the infusion of the drugs. Lidocaine and particularly ketamine were associated with frequent side-effects, the most common being somnolence and dizziness. CONCLUSION: Ketamine showed a significant analgesic effect. The clinical usefulness is, however, limited by disturbing side-effects.

Depth of cutaneous analgesia after application of a eutectic mixture of the local anesthetics lidocaine and prilocaine (EMLA cream).

BACKGROUND: EMLA cream, a eutectic mixture of lidocaine and prilocaine, is a topical anesthetic, frequently used to avoid pain during venipuncture and superficial surgery. However, the depth of analgesia needs further exploration. OBJECTIVE: Our purpose was to investigate the depth of cutaneous analgesia after application of EMLA cream. METHODS: In a single-blind crossover study, EMLA cream was applied under occlusion to the left thighs of 16 subjects. Eleven had application times of 60 and 120 minutes. Five subjects had application times of 3 to 4 hours. Approximately 10 minutes after removal of the EMLA cream, a skin biopsy punch (diameter 4 mm) was inserted to a depth of 1 mm into the skin and the subject rated the pain intensity on a visual analogue scale. If there was no pain or if pain was assessed as acceptable, a new biopsy punch was inserted at a new site to the depth of 2 mm. In this manner, the insertion depth was gradually increased in steps of 1 mm down to a maximum of 6 mm. No skin specimens were removed. RESULTS: After 60 and 120 minutes of EMLA application the mean insertion depths with acceptable pain were 2.9 and 4.5 mm (P <.01), respectively. After 3 to 4 hours of application, 6-mm deep insertions were made with acceptable pain in all 5 subjects. CONCLUSION: Skin biopsy punch insertions in steps of 1 mm appear adequate for assessing the depth of cutaneous analgesia. Biopsy punch insertions with acceptable pain can be made to depths of 1 to 2 mm after 60 minutes, to 2 to 3 mm after 120 minutes, and to 6 mm after 3 to 4 hours of EMLA cream application.

Saliva-resistant coating of tablets prevents oral release of penicillin: plasma but not saliva equivalence.

OBJECTIVE: To investigate saliva and plasma concentrations of penicillin after the intake of a conventional phenoxymethylpenicillin (PcV) tablet and a tablet with saliva-resistant coating (PcVsr), both containing 1 g penicillin. METHODS: The study had an open randomized crossover design and involved 24 healthy subjects. Saliva and blood were sampled intermittently for 6 h after tablet intake. RESULTS: Within the first 10 min after tablet intake penicillin was detected in saliva in ten subjects taking PcV and in none taking PcVsr (P < 0.001). These initial saliva concentrations were short-lasting, but in some subjects 50 to 100 times higher than those following the peak concentration in plasma, i.e. at 40 min or more after swallowing. From 40 min and onwards the saliva concentrations of penicillin were very similar for the two formulations. The elimination of high initial saliva concentrations may diminish ecological disturbances of the mouth flora as well as removing the unpleasant taste of penicillin. The plasma concentrations of penicillin were similar for the two formulations throughout the 6-h sampling period and the mean ratio of the area under the plasma concentration-time curve was 99% for PcVsr in relation to PcV, the 90% confidence interval being 86-115%. The corresponding values for the maximum plasma concentration were 108% and 93 127%. The time to maximum concentration was 45 min for PcVsr and 41 min for PcV. Thus, with regard to standard criteria which are based on systemic (plasma) concentrations, the formulations were bioequivalent despite the substantial difference in initial local (saliva) concentrations. CONCLUSION: Saliva-resistant coating of tablets can prevent oral release of penicillin without affecting the plasma concentrations. From a clinical point of view both local and systemic equivalence should be established before bioequivalence is assumed.

Analgesic effect and plasma concentrations of codeine and morphine after two dose levels of codeine following oral surgery.

A double blind randomised cross over investigation was carried out in 25 male patients undergoing two oral surgical extractions, one for each lower wisdom tooth. The two extractions were performed about 6 weeks apart and were carried out under local anaesthesia. One hour after each extraction the patients randomly received 90 or 45 mg codeine. During the following 5 h the patients rated the intensity of their pain on a visual analogue scale. Blood was simultaneously sampled and assayed for codeine and its metabolite morphine. Mean pain intensity difference was just significantly higher after 90 mg codeine compared to 45 mg. The mean plasma concentrations of codeine and morphine were significantly higher after the 90 mg dose. However, for the two dose levels of codeine there was no obvious relationship between the difference in analgesic effect and the difference in the plasma concentration of codeine or morphine. The plasma concentrations of morphine were 2-3% of those of codeine and the levels were relatively low. Local formation of morphine from codeine within the human brain should therefore be investigated. Four patients were unable to demethylate codeine to a detectable plasma concentration of morphine after 90 mg codeine. In those patients the analgesic effect during the first hours was better after 90 mg codeine than after 45 mg. This suggests some analgesic effect of codeine itself.

Ibuprofen plus codeine, ibuprofen, and placebo in a single- and multidose cross-over comparison for coxarthrosis pain.

The analgesic efficacy of 200 mg ibuprofen plus 30 mg codeine, 200 mg ibuprofen and placebo was investigated in a new analgesic evaluation model using single- and repeated-dose administration. The study was a double-blind randomized cross-over investigation in 26 coxarthrosis patients with persistent pain. After a washout period of at least 2 days with paracetamol available as rescue analgesic, each of the 3 treatments was administered in a total of 6 doses during 24 h. The hourly pain intensity was recorded on a 100-mm visual analogue scale (VAS) for 8 h after the 1st and the 6th dose. The pretreatment VAS score was 31-37 mm. After the 1st dose the 8-h mean pain intensity values were 25, 27, and 26 mm after ibuprofen plus codeine, ibuprofen, and placebo, respectively. Following another 5 doses every 4 h the corresponding values were 10, 17 and 29 mm. Repeated administration of both active drugs reduced the pain intensity significantly. The analgesic efficacy of ibuprofen plus codeine was significantly superior to that of ibuprofen which was, in turn, superior to that of placebo. In conclusion, analgesic efficacy was better differentiated after repeated-dose than after single-dose administration. The present study design was able to differentiate between 200 mg ibuprofen plus 30 mg codeine and 200 mg ibuprofen alone in a relatively small number of patients.

Infants and young children metabolise codeine to morphine. A study after single and repeated rectal administration.

1. Codeine was administered rectally to thirteen infants and young children undergoing elective surgery. Nine infants (6-10 months old) received a 4 mg suppository and four children (3-4 years old) an 8 mg suppository. Codeine and its metabolite morphine were measured in plasma by GC/MS. 2. The mean concentrations of codeine at 3, 4 and 5 h after administration were 240, 163 and 123 nmol l-1 in the younger and 309, 251 and 169 nmol l-1 in the older patients. The corresponding concentrations of morphine were 8.3, 7.4 and 4.5 nmol l-1 and 6.8, 5.5 and 2.8 nmol l-1 respectively. One patient in each age group had no detectable amounts of morphine. 3. In the four children, the rectal dose was repeated 6-hourly for four doses. The plasma concentrations of codeine and morphine following the fifth dose were similar to those after the first dose. The mean AUC(0,5 h) of morphine was 1.6% that of codeine. 4. In the infants the mean plasma half-lives of codeine and morphine were 2.6 and 2.5 h. The two infants with the lowest body weights had the longest half-lives. 5. The mean morphine/codeine concentration ratio was 4.3% in the infants and 1.6% in the children, suggesting impaired glucuronidation of morphine in the former group. The hourly concentration ratios were almost identical following the first and fifth dose in the children. 6. We conclude that at the age of 6 months infants are capable of O-demethylating codeine to morphine.

Analgesic efficacy of acetaminophen sustained release.

The analgesic efficacy of acetaminophen sustained release (SR) and acetaminophen immediate plus sustained release (IR + SR) was evaluated in 200 outpatients with pain after oral surgery. Under double-blind conditions SR high dose (2000 mg) or low dose (1000 mg), IR + SR high dose (500 + 1500 mg) or low dose (250 + 750 mg), or acetaminophen standard tablet high dose (1000 mg) or low dose (500 mg) were randomly administered after removal of a lower third molar. The hourly pain intensity was rated on a visual analog scale during 12 hours. The efficacy was based on peak effect (maximum pain intensity difference in percent), pain reduction (mean percentage pain intensity difference), duration of effect (time to remedication) and pain reduction index (pain reduction multiplied by duration of effect). Pain reduction was 37% with the 500-mg tablet and 54% with SR 2000 mg. The peak effect increased from 53% after 1.9 hours for the 500-mg tablet to 67% after 2.6 hours for SR 2000 mg. The SR formulation significantly increased the duration of effect without reduction in peak effect.

The pain intensity at analgesic intake, and the efficacy of diflunisal in single doses and effervescent acetaminophen in single and repeated doses.

A double-blind, randomized analgesic trial was carried out in 150 patients undergoing surgical removal of their 2 impacted lower wisdom teeth. The analgesic efficacy of effervescent acetaminophen 500 or 1000 mg in a 2-dose regimen was compared with that of diflunisal 500 mg in a single dose. Each dose was taken when subjectively needed and the pain intensity was measured on a visual analog scale during the 10-hour period after first medication. The best pain reduction was achieved with diflunisal. The difference between diflunisal 500 mg and acetaminophen 1000 mg was significant, as was that between acetaminophen 1000 and 500 mg. The peak effect after the first dose occurred later but was greater with diflunisal than with acetaminophen. Patients needing analgesics at low pain intensities seemed to discriminate better between treatments, and the efficacy of acetaminophen was weakly dependent on the initial pain intensity. This intensity was difficult to predict, and only a poor correlation was found between the initial pain intensity and the patient's prior estimate of this.

Bioavailability of three commercial preparations of ibuprofen 600 mg.

The pharmacokinetic variables of ibuprofen 600 mg were investigated after administration of Brufen and compared to administration of Burana and Ibumetin. The investigation was carried out as a randomized single-dose crossover study in 17 healthy volunteers. The mean maximum plasma concentrations of ibuprofen were 58, 45 and 54 micrograms/ml after administration of Brufen, Burana and Ibumetin, respectively, the time to reach this being 1.4, 2.1 and 1.6 h, respectively, after administration. The differences between Brufen and Burana were significant. The relative bioavailability was very similar between Brufen and Burana but about 8% lower for Ibumetin and this difference between Brufen and Ibumetin was significant. Thus, different brands of ibuprofen may not be pharmacokinetically interchangeable and the results show that Brufen is superior to either Burana or Ibumetin when considering both the rate and extent of absorption. These findings are clinically interesting since a high and early plasma concentration of ibuprofen seems to be related to increased analgesic efficacy.

Plasma concentrations of codeine and its metabolite, morphine, after single and repeated oral administration.

Plasma concentrations of codeine and its demethylated metabolite, morphine, were determined after single and repeated oral administration of codeine. Twelve healthy volunteers received two doses of codeine 60 mg, 2.8 h apart. In order to achieve steady-state conditions codeine 60 mg was then taken every 8 h for a further five doses. The plasma concentrations of codeine and morphine after the first, second and seventh doses were analyzed by GC-MS. The maximum plasma concentrations of codeine and morphine were reached about 1 h after administration and this time interval did not change on repeated administration. The peak plasma codeine was higher after the second dose of codeine than after the first and the concentration resembled that at steady-state. For morphine, the plasma concentration did not increase significantly after the second dose. Both after a single dose and during steady-state the plasma concentration of morphine was only 2-3% of that of codeine. It seems unlikely that morphine plays a significant role in the analgesic efficacy of single or repeated doses of codeine.

Multiple doses of paracetamol plus codeine taken immediately after oral surgery.

A double-blind randomized analgesic trial was carried out in 180 patients undergoing surgical removal of an impacted lower wisdom tooth. The patients received the first dose of either paracetamol 1000 mg plus codeine 60 mg, paracetamol 500 mg plus codeine 30 mg or placebo immediately after surgery during the effect of the local anaesthetic. The mean pain intensity, the duration of effect and the number of patients needing additional analgesics were all significantly dose related. In the evaluation procedure a pain intensity index was defined which took into account both the efficacy and the duration of effect. In addition, the analgesic efficacy was calculated over a 12 hour period after first medication and thereby including the efficacy of a second dose, if taken. Paracetamol 1000 mg plus codeine 60 mg followed by paracetamol 500 mg plus codeine 30 mg after around 5 hours was a very effective treatment and over 40% of these patients did not need any further pain relief during the evaluation period. In conclusion, an effective analgesic taken immediately after oral surgery reduces the total pain and diminishes the need of analgesics.

Analgesic efficacy after single and repeated doses of codeine and acetaminophen.

A double-blind randomized analgesic trial was carried out in patients suffering from pain after removal of a third molar tooth. In a two-dose regimen, 108 patients received either 60 mg codeine, 500 mg acetaminophen, or 1000 mg acetaminophen. On the day of surgery, the patients assessed their pain intensity hourly on a visual analog scale. The evaluation was carried out during the 10-hour period after first medication. The best pain reducing effects were achieved with 1000 mg acetaminophen. Both the category and position of each tooth were examined in relation to pain intensity; however, the statistical analysis did not reveal any significant correlation. In all treatment groups, the efficacy of the second dose was superior to that of the first, and the most pronounced difference was obtained in patients taking codeine, who increased their pain reduction from 20 to 60 per cent. Clinical comparisons including codeine may therefore be better carried out in a repeated-dose regimen.

Visual analogue scale and the analysis of analgesic action.

A double-blind randomized trial was carried out in 90 male patients suffering from pain after meniscectomy. The patients received a single dose of paracetamol 1000 mg plus codeine 60 mg, paracetamol 1000 mg, codeine 60 mg, or placebo. The tablets were taken when needed after surgery and the postoperative pain was recorded on a visual analogue scale. Over a period of 4 h the efficacy of the drugs was calculated in terms of pain intensity, pain intensity difference and percentage pain reduction. The greatest effect was obtained in patients taking the paracetamol plus codeine combination. Statistical analysis was carried out by use both of parametric and non-parametric procedures. The results suggest that pain reduction is a valuable measurement of analgesic efficacy and that non-parametric assumptions are preferable in the statistical analysis of analgesic activity.

Effect of preoperative paracetamol on pain after oral surgery.

A double-blind, randomized cross-over trial was carried out in 50 patients undergoing surgical removal of bilaterally impacted lower wisdom teeth. Surgery in each patient was performed twice and paracetamol 1000 mg was administered once preoperatively and once postoperatively. The time interval to additional analgesic intake and the pain intensity up to and at that time were assessed. There was no difference between the 2 treatments. It was concluded that preoperative paracetamol does not offer any clinical advantage in patients who undergo surgical removal of impacted lower wisdom teeth.

Paracetamol plus supplementary doses of codeine. An analgesic study of repeated doses.

A double-blind, multicentre analgesic trial was carried out in patients suffering from pain after removal of an impacted lower wisdom tooth. 266 patients were evaluated after random allocation to treatment with paracetamol 500 mg, paracetamol 500 mg plus codeine 20 mg, paracetamol 500 mg plus codeine 30 mg, or paracetamol 500 mg plus codeine 40 mg. On the day of surgery the patients assessed their own pain intensity hourly on a visual analogue scale. The analysis of the results was carried out according to the method which considered repeated dose intake. A statiscally significant dose-response relationship was obtained between the supplementary doses of codeine and analgesic efficacy. In the comparison of side effects, their frequency increased with increasing amounts of codeine. In clinical practice codeine 30 mg appeared to be the optimal supplement for paracetamol 500 mg.

An analgesic study with repeated doses of phenazone, phenazone plus dextropropoxyphene, and paracetamol, using a visual analogue scale.

A double blind randomized analgesic trial was carried out in patients suffering from pain after removal of an impacted lower wisdom tooth. In a repeated dose regimen, 120 patients received one of three different analgesics: phenazone, phenazone plus dextropropoxyphene, or paracetamol. The assessments of pain were made hourly on a visual analogue scale and the evaluation was carried out according to a method which considers repeated dose intake. The analgesic efficacy of 500 mg phenazone was similar to 500 mg of paracetamol. The pain reduction seemed adequate in most patients and no statistical differences were obtained between the treatment drugs. All analgesics were taken when needed, and the time interval from end of operation to first tablet intake, as well as the pain score at first tablet intake, were factors which significantly influenced the efficacy of the drugs. Therefore, these factors may be of significant importance in the evaluation of analgesics in small sample studies.

The visual analog scale in multiple-dose evaluations of analgesics.

A double-blind, randomized trial was carried out in patients suffering from pain after removal of an impacted lower wisdom tooth. The analgesic effects of a codeine preparation (Staralgin), a dextropropoxyphene preparation (Doleron novum), and paracetamol were compared in a multiple-dose study of 94 patients. The assessments of pain were made hourly on a visual analog scale, and the evaluation was carried out according to a method which takes into account both duration of effect and number of tablets taken. The most pronounced pain reduction and the highest proportion of pain-free patients were reached with the dextropropoxyphene preparation. The reported side effects were few and equally distributed among the treatment groups. The method of evaluation is discussed, and it was noted that the pain score at tablet intake might be of significant importance in comparison of analgesics.