Safety and Tolerance of Metamizole in Postoperative Analgesia in Children
Due to the potential serious side effects of metamizole, the use of this drug in children is often a topic of discussion. Therefore, a prospective multicenter observational non-interventional post-marketing safety study aimed to evaluate the safety of using metamizole in children, with an emphasis on hemodynamic, anaphylactic, or respiratory reactions and agranulocytosis.
Introduction
Metamizole has analgesic, spasmolytic, and antipyretic effects. It has been used in clinical practice since 1922 for the treatment of postoperative, colic, cancer, or migraine pain and is favored for effective analgesia and a low frequency of significant adverse effects, especially compared to nonsteroidal anti-inflammatory drugs (NSAIDs).
Methods and Study Progress
The study was conducted at six pediatric clinics in Germany from September 2013 to September 2014, including a total of 1177 children under the age of 6 who underwent surgery and were administered a single dose of perioperative metamizole. The children were monitored from the administration of anesthesia until discharge from the postoperative room.
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Using a standardized case report form, demographic data of the patients, primary and secondary diagnoses, types of surgeries performed, the dose of metamizole administered, data regarding hemodynamic parameters, use of other analgesics and regional blocks, results of pain measurement on the Children's and Infants' Postoperative Pain Scale (ChIPPS), and the incidence of adverse drug reactions were documented.
Results
Data from 1145 participants were analyzed (mean age 35.8 ± 18.1 [0.1–72] months). The average dose of metamizole was 17.3 ± 2.9 (8.3–29.4) mg/kg. The values of the obtained results are presented as the statistical mean ± standard deviation (SD).
Mean arterial pressure remained stable during metamizole infusion (baseline 55.7 ± 1.3 [25–98] mmHg; post-infusion 56.6 ± 11.3 [25–99] mmHg; p < 0.05), as did heart rate (baseline 103.5 ± 20.4 [56–77]; post-infusion 104.3 ± 20.6 [52–175] beats per minute; p < 0.05).
Pruritus, swelling, and rash were observed – each symptom in only one patient respectively (total incidence 0.3%; 95% confidence interval [CI] –0.035 to 0.56). No respiratory adverse events directly linked to metamizole administration or any laboratory results consistent with agranulocytosis were recorded.
Summary and Conclusion
A single intravenous dose of metamizole for the prevention or treatment of postoperative pain was well-tolerated in more than 1000 children younger than 6 years. The likelihood of serious adverse events (hemodynamic, anaphylactic, or respiratory reactions) is less than 0.3%. The number of patients involved and the observation period were not sufficient to capture an agranulocytosis episode; however, there are generally no records of agranulocytosis occurring in children following a single dose of metamizole in the context of postoperative analgesia.
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Source: Fieler M., Eich C., Becke K. et al. Metamizole for postoperative pain therapy in 1177 children: a prospective, multicentre, observational, postauthorisation safety study. Eur J Anaesthesiol 2015; 32 (12): 839–843, doi: 10.1097/EJA.0000000000000272.
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