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METAMIZOLE SODIUM

Metamizole sodium, also known as dipyrone, is a non-opioid analgesic drug with pain-relieving, fever-reducing, and anti-inflammatory properties. Despite being banned in some countries due to potential side effects, it remains widely used in many parts of the world for managing pain and fever. This article explores how metamizole sodium is being investigated in various clinical trials, examining its effectiveness in different medical conditions, its pharmacokinetic properties, and its potential advantages and limitations compared to other pain medications. The research spans multiple applications including post-operative pain management, renal function effects, pediatric use, and chronic pain treatment.

## Table of Contents

What is Metamizole Sodium?

Metamizole sodium, also known as dipyrone, is a non-opioid medication with powerful analgesic (pain-relieving), antipyretic (fever-reducing), and spasmolytic (muscle relaxant) properties. It belongs to the pyrazolone class of drugs and has been used in clinical practice for decades in many countries worldwide [1]. Despite its widespread use in Europe, Latin America, and parts of Asia, metamizole is not available in some countries, including the United States, due to concerns about rare but serious side effects.

Metamizole is marketed under various brand names in different countries, including Novalgin, Pyralgin, and Dipyrone [2]. This medication is valued for its effectiveness in treating various types of pain and its favorable gastrointestinal and cardiovascular side effect profile compared to traditional non-steroidal anti-inflammatory drugs (NSAIDs).

Medical Uses and Effectiveness

Metamizole sodium is primarily used to treat various forms of pain and reduce fever. Clinical research has demonstrated its effectiveness in multiple scenarios:

  • Acute pain management: Metamizole is effective for treating post-operative pain after various surgical procedures including craniotomy, abdominal surgery, shoulder surgery, and tooth extraction [3][4].
  • Fever reduction: Research shows metamizole is effective as an antipyretic therapy in conditions like acute ischemic stroke [5].
  • Chronic pain: Clinical trials have investigated metamizole’s efficacy in treating chronic neoplastic (cancer-related) pain [6].
  • Low back pain: Studies have evaluated metamizole for treating acute and subacute low back pain, where it has shown good efficacy [7].
  • Renal colic: Metamizole is used for pain relief in patients with kidney stones [8].

Clinical trials have demonstrated that metamizole can be as effective as NSAIDs like ibuprofen and diclofenac for pain management, while potentially offering a better safety profile for certain patients, particularly those with gastrointestinal or cardiovascular risks [9].

How Metamizole Works

Metamizole has multiple mechanisms of action that contribute to its pain-relieving, fever-reducing, and anti-inflammatory effects:

  • COX enzyme inhibition: Like NSAIDs, metamizole inhibits cyclooxygenase (COX) enzymes, particularly COX-1 and COX-2, which are involved in producing prostaglandins that trigger pain, inflammation, and fever [10].
  • Endocannabinoid system activation: Research suggests metamizole activates the endocannabinoid system, which plays a role in pain modulation [10].
  • Opioidergic system effects: Metamizole appears to interact with the opioid system in the body, enhancing its pain-relieving effects without causing the typical side effects associated with opioid medications [10].

Unlike traditional NSAIDs, metamizole is not officially classified as an NSAID, which partially explains its different side effect profile. While it does inhibit COX enzymes, it appears to do so through different mechanisms and with potentially less impact on the gastrointestinal tract and cardiovascular system [7].

Administration Methods and Dosages

Metamizole can be administered through multiple routes, allowing for flexibility in various clinical settings:

  • Oral administration: Commonly used in tablet form, typically at doses of 500-1000 mg three to four times daily [7].
  • Intravenous (IV) administration: Often used in hospital settings for acute pain or when oral administration is not possible. Typical IV doses range from 1-2.5 grams [3].
  • Pediatric dosing: Clinical studies have investigated metamizole in children, with doses typically calculated based on body weight (e.g., 10-15 mg/kg) [2].

Dosing recommendations may vary based on the specific condition being treated, the patient’s age, weight, and overall health status. For chronic conditions, metamizole is sometimes used as part of a multimodal pain management approach, often combined with other analgesics like paracetamol (acetaminophen) [11].

Comparison with Other Pain Medications

Several clinical trials have compared metamizole to other commonly used pain medications:

  • Metamizole vs. NSAIDs: Studies have compared metamizole with NSAIDs like ibuprofen, diclofenac, and naproxen. Results indicate that metamizole provides comparable pain relief with potentially fewer gastrointestinal side effects [9].
  • Metamizole vs. Paracetamol: Research comparing metamizole with paracetamol (acetaminophen) suggests that metamizole may provide more effective pain relief in certain conditions, particularly in post-operative settings [3].
  • Combination therapy: Several studies have investigated the benefits of combining metamizole with other analgesics. For example, the combination of metamizole and ibuprofen has been studied for post-extraction dental pain, showing potential benefits of the combined approach [12].

In some clinical scenarios, metamizole is particularly valuable when NSAIDs are contraindicated, such as in patients with gastrointestinal ulcers, kidney problems, or certain cardiovascular conditions [4].

Effects on Kidney Function

One area of particular interest in metamizole research is its effect on kidney function, especially compared to NSAIDs which are known to potentially cause kidney problems:

A randomized clinical trial investigating the effect of metamizole on renal function in salt-depleted healthy subjects compared it with naproxen (an NSAID). The study aimed to characterize the renal effects of metamizole by measuring glomerular filtration rate (GFR) using inulin clearance [1].

Clinical experience suggests better renal tolerability of metamizole, possibly due to less potent COX inhibition compared to classical NSAIDs. This could make metamizole a valuable alternative for treating painful conditions in patients with impaired renal function [1].

Secondary outcomes in this kidney study included the measurement of urinary excretion of prostaglandin E2 (PGE2) and the prostaglandin I2 (PGI2) metabolite, as well as the urinary excretion of sodium and potassium. These measurements help to understand how metamizole affects kidney function at the biochemical level [1].

Pharmacokinetics in Different Populations

Understanding how metamizole is processed in the body (its pharmacokinetics) is crucial for safe and effective use:

Pediatric pharmacokinetics: A study assessed the pharmacokinetic parameters of metamizole following intravenous administration in children less than 6 years of age. This research is important because there were no published pharmacokinetic studies of metamizole in pediatrics, and intravenous administration is commonly used for post-operative analgesia in children [2].

The study measured parameters such as the area under the plasma concentration-time curve (AUC), maximum plasma concentration (Cmax), time to reach maximum concentration (tmax), and half-life (t½) for metamizole and its metabolites. These measurements help determine the appropriate dosing for children of different ages and weights [2].

Metabolism and elimination: After administration, metamizole is rapidly hydrolyzed to its active metabolite 4-methylaminoantipyrine (4-MAA), which is then further metabolized to other compounds including 4-aminoantipyrine (4-AA), 4-acetylaminoantipyrine (4-AAA), and 4-formylaminoantipyrine (4-FAA). These metabolites are primarily eliminated through the kidneys [10].

Drug Interactions

Understanding potential interactions between metamizole and other medications is important for safe use:

A study investigating the interaction of metamizole with the cytochrome P450 system (which metabolizes many drugs in the liver) found that metamizole may affect the metabolism of other medications. This interaction potential was assessed using the “Basel Cocktail,” which contains specific substrates for different CYP enzymes [10].

Another study specifically looked at how CYP inhibition affects metamizole metabolism. This helps identify which medications might interact with metamizole when taken concurrently [13].

These studies are important because they help healthcare providers predict and avoid potential drug interactions that could either reduce metamizole’s effectiveness or increase the risk of side effects.

Side Effects and Safety Profile

Like all medications, metamizole has potential side effects that should be considered:

  • Common side effects may include nausea, vomiting, and allergic reactions [3].
  • Agranulocytosis: The most concerning but rare adverse effect associated with metamizole is agranulocytosis, a severe reduction in white blood cell count that can increase susceptibility to infections. This concern has led to its withdrawal from the market in some countries, including the United States [7].
  • Safety comparison: Despite concerns about agranulocytosis, some studies suggest that metamizole may have a more favorable overall safety profile compared to NSAIDs, particularly regarding gastrointestinal, cardiovascular, and renal side effects [7].

The risk of agranulocytosis is estimated to be very low (approximately 1 case per million treatments), but it can be serious when it occurs. For this reason, patients taking metamizole should be monitored for signs of infection, such as fever, sore throat, or mouth ulcers, which could indicate this rare complication [7].

Special Clinical Applications

Metamizole has been studied in several specialized clinical scenarios:

  • Shoulder surgery: Research has evaluated the added value of metamizole to standard postoperative treatment after ambulant shoulder surgery, showing it can be effective for pain management in this setting [4].
  • Neuraxial anesthesia: Studies have combined metamizole with neuraxial anesthesia techniques for procedures like cesarean sections [14].
  • Intrapartum fever: Metamizole has been compared with acetaminophen for treating maternal fever during labor [15].
  • Acute pancreatitis: The effectiveness of metamizole in combination with other analgesics has been studied for pain management in acute pancreatitis in children [16].

In many of these specialized applications, metamizole has shown good efficacy and tolerability, making it a valuable option in multimodal pain management strategies [11].

Area of Investigation Key Findings and Applications Patient Population
Renal Function Being compared to naproxen in salt-depleted subjects to assess effects on glomerular filtration rate (GFR) and urinary prostaglandin excretion. May be better tolerated renally than traditional NSAIDs. Healthy adult subjects (salt-depleted)
Pediatric Use Being studied to determine pharmacokinetics in children under 6 years, as currently there are no official dosing recommendations for infants under 9kg despite common “off-label” use. Children 3-72 months undergoing elective surgery
Drug Interactions Being investigated for potential interactions with the cytochrome P450 system, which could affect how it interacts with other medications. Healthy adult subjects
Post-operative Pain Being studied in various surgical settings including craniotomy, shoulder surgery, and thoracotomy. Often compared with or added to standard treatments like paracetamol. Adult surgical patients
Low Back Pain Being compared to ibuprofen for effectiveness in treating acute low back pain, with a focus on whether it is non-inferior to ibuprofen. Adults with acute low back pain
Dental Applications Being studied in combination with ibuprofen for post-extraction pain after third molar removal. Dental patients
Fever Reduction Being evaluated for effectiveness as an antipyretic therapy in conditions like acute ischemic stroke. Adults with acute ischemic stroke
Chronic Cancer Pain Being studied for potential to reduce morphine requirements in patients with moderate to severe chronic cancer pain. Cancer patients with chronic pain

FAQ

  • What is metamizole sodium and what is it used for? Metamizole sodium (also known as dipyrone) is a non-opioid medication with analgesic (pain-relieving), antipyretic (fever-reducing), and spasmolytic (muscle-relaxing) properties. Clinical trials are investigating its use for various conditions including post-operative pain after surgeries (such as shoulder surgery, craniotomy, and thoracotomy), acute low back pain, dental pain, and as an antipyretic therapy in conditions like stroke and during labor. It's being studied both as a standalone treatment and in combination with other medications as part of multimodal pain management approaches.
  • How does metamizole compare to other pain medications? Clinical trials are comparing metamizole to medications like paracetamol (acetaminophen), ibuprofen, diclofenac, and naproxen. One study is investigating whether metamizole is non-inferior to ibuprofen for acute low back pain. Another study is comparing metamizole to paracetamol for post-operative pain after ambulatory surgery. A key advantage of metamizole compared to NSAIDs (like ibuprofen) appears to be its favorable gastrointestinal and cardiovascular side effect profile, making it potentially suitable for patients who cannot take NSAIDs. However, its effectiveness compared to other medications varies depending on the specific condition being treated.
  • What are the potential side effects of metamizole? While metamizole has a favorable gastrointestinal and cardiovascular profile compared to NSAIDs, it carries a controversial risk of agranulocytosis (a severe reduction in white blood cell count). This is a rare but serious side effect that has led to the drug being banned in some countries. Clinical trials are monitoring for adverse events to better understand the safety profile. One study specifically notes that 'the overall risk of agranulocytosis is increased compared to other drugs, but it only occurs in a small proportion of susceptible patients, and the overall safety profile of metamizole is still favorable compared to other analgesics such as NSAIDs or opioids.'
  • How is metamizole being used in post-surgical pain management? Metamizole is being studied in various surgical settings, including shoulder surgery, craniotomy, thoracotomy, laparoscopic sleeve gastrectomy, and dental procedures. It's being investigated both as an intravenous medication during and after surgery, and as an oral medication for home use after ambulatory (outpatient) surgeries. In some studies, it's used as part of multimodal analgesia, combined with medications like paracetamol or as an alternative to NSAIDs. For example, one trial is investigating the addition of metamizole to standard post-operative treatment after ambulatory shoulder surgery to see if it improves pain control, particularly in cases where NSAIDs are contraindicated.
  • Can metamizole be used in children? Yes, metamizole is being studied for use in children. One clinical trial is specifically investigating the pharmacokinetics (how the drug moves through the body) of metamizole following intravenous administration in children less than 6 years of age. This study aims to determine appropriate dosing guidelines for children, especially for those weighing less than 9 kg, for whom there are currently no official dosing recommendations. The study notes that despite the lack of data, intravenous metamizole is frequently used for post-operative pain management in pediatrics, including in infants weighing less than 9 kg, though this use is considered 'off-label.'

Ongoing Clinical Trials on METAMIZOLE SODIUM

  • Study on Ropivacaine and Lidocaine for Reducing Pain After Tonsil Removal in Patients with Chronic Tonsillitis

    Recruiting

    3 1 1 1
    Investigated diseases:
    Investigated drugs:
    Austria

References

  1. https://clinicaltrials.gov/study/NCT01995006
  2. https://clinicaltrials.gov/study/NCT02660177
  3. https://clinicaltrials.gov/study/NCT04720248
  4. https://clinicaltrials.gov/study/NCT04703257
  5. https://clinicaltrials.gov/study/NCT02184260
  6. https://clinicaltrials.gov/study/NCT02181920
  7. https://clinicaltrials.gov/study/NCT04111315
  8. https://clinicaltrials.gov/study/NCT03529097
  9. https://clinicaltrials.gov/study/NCT01858402
  10. https://clinicaltrials.gov/study/NCT03990129
  11. https://clinicaltrials.gov/study/NCT04082728
  12. https://clinicaltrials.gov/study/NCT02686021
  13. https://clinicaltrials.gov/study/NCT04621253
  14. https://clinicaltrials.gov/study/NCT03404908
  15. https://clinicaltrials.gov/study/NCT06950840
  16. https://clinicaltrials.gov/study/NCT07024199