Dipyrone (metamizol) — a never ending story

Pharmacokinetics of metamizole (dipyrone) as an add-on in calves undergoing umbilical surgery

This preliminary clinical investigation of the pharmacokinetic behavior of the main metamizole (dipyrone) metabolites 4-methylaminoantipyrine (4-MAA) and 4-aminoantipyrine (4-AA) in calves undergoing umbilical surgery is part of an already published main study. A single intravenous dose of metamizole was added to ketamine/xylazine/isoflurane anesthesia. Eight Simmental calves weighing 90 ± 10.8 kg and aged 47.6 ± 10.4 days received 40 mg/kg metamizole intravenously 10 minutes prior to general anesthesia. Blood samples were collected over 24 hours and analyzed for 4-MAA and 4-AA. Meloxicam was additionally given twice: 2.5 hours pre- and 20.5 hours postsurgically. The pharmacokinetic profile of 4-MAA was best fitted to a two-compartment model and was characterized by a fast distribution half-life and slow elimination half-life (t_½alpha = 5.29 minutes, t_½beta = 9.49 hours). The maximum concentration (C_max 101.63 μg/mL) was detected at the first measurement time point 15 minutes after administration. In contrast, 4-AA showed fast, high and biphasic plasma peak concentration behavior in five calves (2.54–2.66 μg/mL after 15–30 minutes, and 2.10–2.14 μg/mL after 2–3.5 hours) with a t_½beta of 8.87 hours, indicating a rapid distribution and subsequent redistribution from well-perfused organs. Alternatively, three calves exhibited a slower and lower monophasic plasma peak concentration (1.66 μg/mL after 6.5 hours) with a t_½beta of 6.23 hours, indicating slow accumulation in the intravascular compartment. The maximum concentration and area under the plasma concentration curve (AUC) of 4-AA were lower than those of 4-MAA. This metabolic behavior supports our already published data on clinical monitoring and plasma cortisol concentrations (PCCs). Compared to those of saline controls, lower PCCs correspond to the t_½alpha of 4-MAA. Data on T_max and t_½beta also match these clinical observations. However, further studies are required to assess the exact analgesic mechanism and potency of the metamizole metabolites in calves.

Solid-phase extraction followed by liquid chromatography-time-of-flight-mass spectrometry to evaluate pharmaceuticals in effluents. A pilot monitoring study

The present work provides a multi-residue analytical method for determining a selection of 20 pharmaceuticals from diverse therapeutical classes in hospital effluent wastewater. The method is based on the simultaneous extraction of the target compounds by solid phase extraction (SPE), followed by liquid chromatography-time-of-flight-mass spectrometry (LC-TOF-MS) analysis. Using TOF-MS, accurate mass measurements within 2 ppm error were obtained for most of the pharmaceuticals studied. Empirical formula information can be obtained by this method, allowing the unequivocal identification of the target compounds in the samples. Validation studies showed that LC-TOF-MS analysis is a valuable new tool for identification and quantification of pharmaceuticals in wastewater. Recoveries, using Oasis HLB cartridges at pH 7, were higher than 75% for all pharmaceuticals, except for ranitidine, 4-methylaminoantipyrine (4-MAA), cefotaxime and omeprazole, which needed specific pH conditions for their extraction. Linearity of response over two orders of magnitude was demonstrated (r > 0.99). Matrix effects resulting in suppression of the response were observed. For most of the compounds ion suppression was less than 39%, except for metronidazole, carbamazepine 10,11-epoxide, naproxen and erythromycin, where the signal suppression was 42%, 59%, 46% and 95%, respectively. A simple and effective approach to minimize or avoid matrix interferences was the 1 : 4 dilution of the SPE extracts. Method detection limits (MDLs) and quantification limits (MQLs) ranged between 4-115 ng l(-1) and 14-384 ng l(-1), respectively. The precision of the method, calculated as relative standard deviation (RSD), ranged from 1.1-19.8% and 1.7-21.7% for intra- and inter-day, respectively. The developed analytical method was applied to the analysis of hospital effluent wastewater during a survey study. 18 of the 20 pharmaceuticals studied were detected at concentration levels of microg l(-1), reaching in some cases concentrations over 100 microg l(-1), and in the case of the analgesic and antipyretic dipyrone metabolite, higher than 1000 microg l(-1).

A comparison between IV paracetamol and IV metamizol for postoperative analgesia after retinal surgery

OBJECTIVE

To assess clinical efficacy of IV paracetamol 1 g and IV metamizol 1 IV metamizol 1 g on a 24-h dosing schedule in this randomized, double-blinded, placebo-controlled study of 38 ASA physical status I-III patients undergoing retinal surgery.

RESEARCH DESIGN AND METHODS

General anaesthesia using remifentanil, propofol, and desflurane was performed for surgery. The patients were randomly allocated to three groups, receiving infusions of paracetamol 1 g/100 mL (Para Group), of metamizol 1 g/100 mL (Meta Group), or of 100 mL of saline solution as placebo control (Plac Group) 30 min before arrival in the recovery area and every 6 h up to 24 h postoperatively. All patients had unrestricted access to intravenous opioid rescue medication.

MAIN OUTCOME MEASURES

The primary efficacy variables were pain scores at rest over 30 h postoperatively analysed by using repeated ANOVA measurement. Secondary efficacy variables were pain scores on coughing, also analysed by repeated ANOVA measurement.

RESULTS

Five patients in the Plac Group and one patient in the Meta Group interrupted the study protocol. Regarding pain scores at rest, Mauchly-test of sphericity was significant (p = 0.03). For the p time effects a significant result was detected (p < 0.001). The main effect between the three treatment groups was significantly different (p = 0.01). The Bonferroni adjusted pair wise comparisons between p the Plac Group and the Para Group showed a significant difference in favour of IV paracetamol (p = 0.024; mean difference 14.8; p 95% CI 1.6-28.0), between the Plac Group and the Meta Group in favour of IV metamizol (p = 0.025; mean difference 14.4; 95% CI p 1.5-27.4), and no significant difference between the Para Group and the Meta Group (p = 1.0; mean difference 0.4; 95% CI-12.8 to 13.6). Pain scores on coughing showed a significant different main effect between the three treatment groups (p = 0.022). The Bonferroni adjusted pair wise comparisons between the Plac Group and the Para Group showed a significant difference in favour of IV paracetamol (p = 0.032; mean difference 17.9; 95% CI 1.3-34.6), a p difference, though not reaching statistical significance, in favour of IV metamizol between the Plac Group and the Meta Group (p = 0.081; p mean difference 15.0; 95% CI -1.4 to 31.4), and no significant difference between the Para Group and the Meta Group (p = 1.0; p mean difference 2.9; 95% CI -13.8 6 to 19.6). None of the patients experienced itching; one patient in the Meta Group developed a mild erythema. There was no statistical difference in the incidence of nausea (Plac vs. Para Group: p = 0.94, Plac vs. Meta Group: p = 0.98, Para vs Meta Group: p = 0.95) or vomiting (Plac vs. Para Group: p = 0.73, Plac vs. Meta Group: p = 0.85, Para vs Meta Group: p = 0.86) between the groups. Patients in the Plac Group experienced significantly more often sedation than patients in the Meta Group (p = 0.049). There was a trend of higher sedation in the Plac Group than in the Para Group, which did not reach statistical significance (p = 0.07). There was no difference in sedation between the Meta and the Para Groups (p = 0.84).

CONCLUSION

IV paracetamol 1 g has a similar analgesic potency as IV metamizol 1 g for postoperative analgesia after retinal surgery.

Impact of CYP2D6 genotype on postoperative tramadol analgesia

Genetic polymorphisms result in absent enzyme activity of CYP2D6 (poor metabolizers, PM) in about 10% of the Caucasian population. This study investigates whether the PM genotype has an impact on the response to tramadol analgesia in postoperative patients. A prospective study design was used and 300 patients recovering from abdominal surgery were enrolled. After titration of an individual loading dose, patients could self-administer 1 ml bolus doses of the drug combination tramadol 20 mg/ml, dipyrone 200 mg/ml and metoclopramide 0.4 mg/ml via patient-controlled analgesia (PCA). Patients' genotype was analyzed considering the most prevalent PM associated CYP2D6 mutations using a real-time PCR and hybridization based genotyping method. Demographic data, surgery related variables, pain scores, analgesic consumption and need for rescue medication were compared between extensive metabolizers (EM) and PM. The primary outcome criterion 'response' was defined as responder or non-responder status by the need for rescue medication and patients' satisfaction at the final interview. Demographic and surgery related data were comparable between EM (n=241) and PM (n=30). The percentage of non-responders was significantly higher in the PM group (46.7%) compared with the EM group (21.6%; p=0.005). Tramadol loading dose amounted to 108.2+/-56.9 and 144.7+/-22.6 mg (p<0.001) in EM and PM, respectively. More patients displaying the PM genotype needed rescue medication in the recovery room and during PCA period than patients with at least one wild type allele (21.6 versus 43.3%, p=0.02). PM for CYP2D6 showed a lower response rate to postoperative tramadol analgesia than EM. Therefore, CYP2D6 genotype has an impact on analgesia with tramadol. Pharmacogenetics may explain some of the varying response to pain medication in postoperative patients.

Postoperative analgesia at home after ambulatory hand surgery: a controlled comparison of tramadol, metamizol, and paracetamol

We compared in a prospective, randomized, double-blinded study the analgesic efficacy of three drugs in 120 ASA I and II patients scheduled to undergo ambulatory hand surgery with IV regional anesthesia. At discharge, oral analgesic tablets were prescribed as follows: tramadol 100 mg every 6 h, metamizol 1 g every 6 h, and paracetamol (acetaminophen) 1 g every 6 h. Rescue medication consisted of oral dextropropoxyphene 100 mg on demand. Analgesic efficacy was evaluated by self-assessment of pain intensity by visual analog score at six different time intervals during the 48-h study period. Patients also recorded global pain relief on a 5-grade scale, total number of study and rescue analgesic tablets, frequency and severity of adverse effects, sleep pattern, and overall satisfaction. None of the study drugs alone provided effective analgesia in all patients. The percentage of patients who required supplementary analgesics was 23% with tramadol, 31% with metamizol, and 42% with acetaminophen. Tramadol was the most effective analgesic, as evidenced by low pain scores, least rescue medication, and fewest number of patients with sleep disturbance. However, the incidence of side effects was also increased with tramadol. Seven patients (17.5%) withdrew from the study because of the severity of nausea and dizziness associated with the use of tramadol. Metamizol and acetaminophen provided good analgesia in about 70% and 60% of patients, respectively, with a decreased incidence of side effects. Despite receiving oral analgesic medication, up to 40% of patients undergoing hand surgery experienced inadequate analgesia in this controlled trial. Although tramadol was more effective, its use was associated with the highest frequency and intensity of adverse effects and the most patient dissatisfaction. Metamizol and acetaminophen provided good analgesia with a small incidence of side effects. For patients undergoing ambulatory hand surgery, postoperative pain can last longer than 2-3 days, and there is a need for both better education before the procedure and oral analgesic therapy at home.