15/10/2025
There is ongoing debate in Spain about the safety of using Metamizole/Novalgin so we thought we’d shed some light on the matter.
Metamizole is a pyrazolone derivative. Its exact mechanism is not fully understood, but evidence points to:
• Central COX inhibition → reducing prostaglandin synthesis (analgesic and antipyretic effects).
• Spasmolytic action → relaxation of smooth muscle, particularly in biliary and urinary tract colic.
• Possible endocannabinoid system modulation → contributing to analgesic effect.
✅ Pros (Why clinicians in many countries use it)
1. Strong Analgesic: Comparable in effect to weak opioids, often stronger than paracetamol or standard NSAIDs for moderate to severe pain.
2. Antipyretic: Highly effective in refractory fever unresponsive to paracetamol or NSAIDs.
3. Spasmolytic effect: Uniquely useful in renal colic, biliary colic, and severe abdominal pain.
4. Low gastric toxicity: Unlike NSAIDs, it does not significantly cause gastric ulcers or bleeding.
5. No major renal vasoconstriction: Safer than NSAIDs in terms of renal perfusion, particularly in hypovolaemic patients.
6. No direct platelet inhibition: Unlike aspirin or other NSAIDs, so less risk of bleeding.
7. Parenteral administration: Can be given IV or IM, making it useful in acute hospital settings.
❌ Cons (Why it is banned in the UK and some other countries)
1. Risk of agranulocytosis:
• Rare but potentially fatal (estimated 1 in 10,000 to 1 in 1,000,000 exposures depending on population genetics and surveillance).
• Leads to severe neutropenia, sepsis, and death if not detected early.
• This is the main reason the UK, USA, and parts of Northern Europe prohibit its use.
2. Regulatory uncertainty:
• Incidence of agranulocytosis appears higher in Northern Europe than in Latin America or Southern Europe, raising questions of genetic susceptibility.
3. Other adverse reactions:
• Hypotension and anaphylaxis (particularly with IV use).
• Rare cases of hepatotoxicity and renal impairment.
4. Safer alternatives available:
• Paracetamol for mild/moderate pain and fever.
• NSAIDs for inflammatory pain (with gastric/renal precautions).
• Opioids (though problematic) for severe pain.
Because of this therapeutic redundancy, regulators in the UK judged the benefit–risk ratio unfavourable.
🌍 Global Use
• Widely prescribed in Spain, Germany, Russia, Latin America, and much of Asia. In countries like Brazil, it’s one of the most commonly used painkillers.
• Banned in the UK, US, and some Scandinavian countries because of agranulocytosis concerns.
⚖️ Balanced Clinical View
• In high-prevalence agranulocytosis regions (UK, Scandinavia), regulators say not worth the risk.
• In other regions (Spain, Germany, Latin America), where reported incidence is lower, many physicians consider it safe and valuable, especially when NSAIDs are contraindicated (renal impairment, gastric ulcer risk).
• WHO stance: Lists metamizole as an essential medicine in some contexts but flags the agranulocytosis risk.
👉 Bottom line, if we were advising a UK patient:
• It wouldn’t be prescribed in the UK, because regulatory bodies (MHRA, NICE) deem the risk unacceptable when other options exist.
• But if a patient is abroad and prescribed metamizole (say, in Spain for renal colic), I’d reassure them it can be safe short-term, provided they’re monitored and discontinue at the first sign of fever, sore throat, or infection (possible agranulocytosis).
